Model Boat Mayhem - Forum

Technical, Techniques, Hints, and Tips => BRUSHLESS Motors and Speed Controllers => Topic started by: andrewh on October 29, 2008, 02:05:07 PM

Title: Brushless Basics
Post by: andrewh on October 29, 2008, 02:05:07 PM
Brushless motors – a basic guide

Page no.1 - who. why and waht do we need to know?

Judging by the questions asked on the forum we could all do with a run through the basics.  I may be well placed to start laying this out because:
•   I don’t know the answers – but would like to
•   I have, use and make Brushless motors (but for aircraft and Higgins Hellkittens)
•   I like, myself, to know the basics before spending any money

It would be a good idea to make this as broad and informative as possible.  Comments, additions experience and suggestions are genuinely welcome.

An area I know nothing about is boats and propellers!  If anyone knows the relationships between props, power, pitch, boat speed and the precession of the equinoxes I will undertake to try and produce a calculator to make some of the things calculable!

What are they, exactly?
Well; they are electric motors, same as the ones we are used to, and have the same basic habits meaning:
They must run at design speed to be efficient
If overloaded (too big a prop) they will slow down and absorb more power until they find a speed where the power input matches the load.
Conversely, if the prop is small they will spin faster and take much less current (and often be more efficient)

They are Alternating Current (AC) motors! 
So how do they run off our batteries, then?  Brushless motors need a special ESC which chops up the DC voltage into 3-phase AC and feeds it into the motor wires.  Speed control comes from the way the ESC drives the phases round, and the VERY cunning bit is the timing.

Brief diversion into 3-phase AC  -optional reading
The brushless motor has three sets of windings (one per phase).  The rotor has a set of magnets (now always rare-earth magnets) which are not quite lined up with the stator poles (often there are 9 stator poles and 12 magnets).  When one phase is energised it attracts the set of magnets which are nearest and pulls the rotor round, then the next phase is energised with the same results, then the third phase.  Repeat thousands of times a second.

The speed of rotation of the phases is governed by the throttle setting, and the timing of when the current in a phase is switched on is also important.  The required timing changes with the speed (like in a car engine), the load, the type of motor and various other things.  Some ESCs are adjustable in timing, and several have a few settings to select among.  I believe that ALL brushless ESCs are delivered with a nice average set of settings and will operate well when plugged in to nearly any motor and will start and run with any average load.

They are also generators, just like DC motors.  If they are driven by their load they push power back into the supply.  The power will appear as (surprisingly) 3-phase AC, and when you see small wind turbines this is what most of them are doing and using!

What happens if I plug a brushless motor directly to a battery?
Don’t try this at home!Now that you have read the description of how they operate you will be able to work out the answer. 
If you do it you will have connected one of the phases across the battery – the rotor will kick instantly till the magnets are next to that set of poles.  Then nothing more will happen until smoke curls out of the motor because you still have the battery connected to three coils and they are getting HOTTER.
With a high-power battery the motor will be damaged if it goes on for too long (a second or two depending on the wind (but your could always rewind it rather than scrapping it!).

Types of Brushless MotorsThere are only three types that the modelling fraternity will use, and boat modellers will probably only meet one type.  However some of us may wish to drive huge paddles directly and efficiently so I will mention, both types:
1.   Brushless motors (there really doesn’t seem to be another name)
2.   LRK motors
3.   Printed motors

If I define and dispose of LRK motors quickly.  They are a family of brushless motors designed for high magnetic efficiency.  Because of this they are also electrically efficient.  They tend to be large diameter and flat (pancake shape) and therefore produce huge torques, but seldom high revs (and will run off many ordinary brushless ESCs).  Used for application like electric bicycles and other vehicles.
For more information Google “LRK motors” or look through
LRK are the initials of the gentlemen who have developed them.

Printed motors – instead of physically winding coils on the stator it is possible to use a printed circuit to act as the current carrying conductor.  I have not met one of these motors in the flesh, but the gent from Model Motors Direct has referred to them in a couple of years ago in one of the comics.  Printed circuit board being what it is the coils have to be spread over an area, so these motors are going to be large diameter and very flat (usually there is a printed board each side of a rotor with magnets inserted into it or bonded on)  So printed motors are round and very flat, and should be high torque, low current devices (the printed tracks are not going to carry as much current as a wire)
Should be cheap. Though!.

“Chapters” I have in mind to follow on with include: (but are not limited to)

1.   Inrunners/Outrunners differences, similarities
2.   Matching an existing motor
3.   Gearboxes, belt drives, etc
4.   Kv for fun and profit
5.   Why would I want to change to a brushless?
6.   Boat speed, motor revs, voltage?
7.   Mounting the beasts
8.   Reversing – how do I do this
9.   Speed control
10.   Why would I be interested in 4-D flying?? :}

Comments, contributions etc, welcomed
It is always valid to guide me to say more, less or nothing at all

Sorry no illustrations yet - other folk have found and posted diagrams of how they work, etc - I will try to break up slabs of text with relevant piccies


Title: Re: Brushless Basics
Post by: Martin [Admin] on October 29, 2008, 02:18:09 PM

Well I've certainly hit the old  (  button to make sure I don't miss anything here!
Thanks Andrew.   :-))
Title: Re: Brushless Basics
Post by: andrewh on November 03, 2008, 02:10:08 PM
Intro, feedback etc.
First;  sorry about the gap before getting this to you.  My day job got manic but we have now shipped the bits that make up my project so now there are some gaps in the day.

Range of sizes
I have not spoken really of size, but brushless motors are made from roughly one gram weight (a few milliwatts) to about 20 megawatts – cruise ships have 4 or 6 of these!  It is likely, therefore that we fall in the range of possible ratings!

Where will we find them?
1)   Electric scooters, motor-bikes and assisted bicycles increasingly use brushless for the same reason that we might – power not wasted as heat in the motor stays in the battery and can be used.  The top-of-the range models nearly always use brushless motors and Lithium cells in case any of us are looking for the ultimate boat power source.  They seem to live in the 400W to 5kW range.  Naturally they use brushless speed controllers (normally with potentiometer speed control, but we know how to add a servo to drive the arm of the pot, don’t we?
2)   Computers
CD-ROM drives and Hard Disc drives are now always (I think) brushless.  In fact using a CDROM motor raw material has led to the “CD” motor  which was , and probably still is the most common brushless motor for electric flight in the “parkflyer” size range.  The CD motor is an excellent example of the Outrunner type (see below)

Shape, and how it affects shaft speed
In the first spiel I realise that I spoke of large diameter motors inevitably running (relatively) slowly.  There are two factors at work here:
1) Torque – the “Twisting power of a motor – we measure this crudely by trying to hold the shaft when the motor is running.  If the force to rotate the motor is generated at a large diameter, the motor will have lots of torque (and power is torque multiplied by revs)
So large diameter motors are likely to produce lots of torque.
2) Strength.  Brushless motors never have rotating windings (as far as we are concerned), but they certainly do spin their magnets on the rotor.
Inrunners have cylindrical rotors with the magnets embedded in the rotor, and the limit of rotational speed is governed by the strength of whatever is retaining the magnets into the rotor, and the diameter of the rotor.  If it spins too fast the magnets will fly outwards with centrifugal force and act as an effective, but noisy brake
Outrunners have a “bell” shape with a cylindrical drum (with magnets in the inside surface) which spins round the stator windings.  Again, centrifugal force attempts to “open” the mouth of the drum and the material of the drum usually steel has to prevent this happening – so there is a practical limit on the revs possible

Essence of Brushless chapter 2

The types of brushless that modellers will come across

Inrunners have their magnets embedded in the rotor which runs inside (hence the name) the stator.  There is an animation of a secctioned inrunner running in:

I see that this animation runs - there is a lot of good general motor information on the site

Inrunners always have the rotor shaft running in two bearings, almost invariably ballraces, so the shaft is well supported.  The shaft end pokes out of a stationary cylindrical motor – exactly the same general format as a DC motor
This little fellow is 13mm diameter and can have a KV up to about 7000 - so on 10V it spins at 70,000 RPM

Recognition features:
Cylindrical case – often the same general proportions as a DCmotor
Relatively small diameter – often about three times as long as the diameter
Case remains stationary
Case sometimes includes cooling – fins, or water-cooling manifold

Watch out, by the way, for the cooling fins – if they run round the case this way
They were intended for helicopters and there just isn’t the same draft in a boat!

Because the case is stationary – these are the only brushless motors which are easily interchangeable with our conventional DC motors, and a lot of them are described as “400 replacements” or “600 size”  be aware that this means physical size, and they will indeed fit in the motor mount, but are capable of producing anything up to 10 times the power and may do so at astronomical revs

Outrunners need a bit of understanding – they too have a stationary stator but it lives inside the rotor.  So the rotor and its magnets are rotating round the outside of the stator and on end of the rotor is closed and is a tight fit – often a press fit on the drive shaft.  The drive shaft runs on bearings inside the stator and can extend out of both ends of the motor to drive whatever we like.

The rotor is a drum or bell shape with one open end, and the magnets are bonded into the inside surface of it – see picture below
So Outrunners are produce their torque at a much greater diameter than inrunners – they produce loads of torque, but you don’t really want to run them at very high speeds, because of the open-ended stator and the relationship of the magnets to the bearings.

Note the generally big diameter, squat shape - the motor mount is at the left, and EVERYTHING to the right of the wires rotates

Some good outrunners are made so that the relationship of the stator and shaft can be changed
On this motor the shaft can be moved to stick out of either or (as shown) both ends of the motor.  The shaft, gold star on the left of the picture, annd black cylinder all rotate, and in this case the motor mount is the gold component at the right hand end.

More as it happens - next chapter we get numerical!

as always  - comments and contributions welcomed

Title: Re: Brushless Basics
Post by: andrewh on November 03, 2008, 02:38:09 PM

Now that should help a boat move right along
Title: Re: Brushless Basics
Post by: kiwimodeller on November 03, 2008, 10:50:15 PM
Even this dummy can understand so far, keep it coming, thanks, Ian.
Title: Re: Brushless Basics
Post by: andrewh on November 06, 2008, 02:18:22 PM
Brushless Basics – Chapter 3
“Attack of the numbers”

We’ll start with a quiz, to see if you have been listening carefully:
Inrunner or outrunner?
Inrunner or outrunner?
Inrunner or outrunner?

Well done, 100% on the quiz – what a model set of students, spoiled only by Carruthers dipping Amanda’s pigtail in the inkwell.

To recap:  
Brushless are 3-phase AC motors and  need a brushless speed controller.
The two flavours we will see are :

Inrunners – Cases are stationary, shaft is supported at both ends; relatively small diameter, relatively high revs (high kv), low torque

Outrunners – all the motor apart from the stator and one backplate rotates.  Relatively large diameter, low revs (low KV), high torque


I am now going to nail my colours to the fence!
A) boat modellers use conventional DC electric motors successfully (on the whole)
B) boat modellers use DC motors VERY gently (with a few exceptions)
C) Brushless motors are much more efficient (over a broader range) than DC motors
D) Boat modellers have a much greater chance of being happy with a brushless motor, even if it is not accurately specified or fed with volts.

Chapter 3 – brushless numbers
Starting with the efficiency – this is the first and relatively important number.  This is not because we might save the world by leaving electricery in the batteries, but because brushless motors are more efficient - and it matters!

Taking the motors on their own, DC motors probably run at around 50% efficient. 
The only people who are likely to exceed this are the drivers of the well-made multipole motors in low speed, low current operation. 
Where does the wasted power go?  What is the water-cooling doing?
If the propeller wastes another 20 to 30% of what is left  we have put a lot of energy into the system to not get very much effective drive out of it.
Speed boats with brushed drives - gross efficiency (propulsive power/motor input power) probably around 30%
Scale boats - warships etc about 50%
Tugs - single large prop    up to 80%

Bigger props driven slowly (preferably without gears) by well made multipole motors at low currents will have the best efficiency in every part of the drive package.

Please treat Graupner's efficiency figures with caution.  I am perfectly sure they are precisely measured and calculated but they are much higher than anyone elses measurements.  My suggestion is to use them as guides only to the relative efficiencies of the Speed range.

Brushless motors have claimed efficiencies around 80 to 95%!  Even if there is some optimism hiding in the claims it is a different type of beast.

Why should there be this difference?
Well; what do brushless motors NOT have?
That's right Amanda, brushes!   :}
In fact its not only brushes but also the things that go with them.  Brushes are basically cunning timed switches as well as sliding gadgets to transfer the current into the motor rotor. 
The timing aspect turns the currents on and off in eack of the coils of the rotor (poles) with the losses that go with making and destroying magnetic circuits, the variation of timing that comes from mechanical movement of the commutator as it heats up, expands, whirls with speed etc, and the inevitable problem of rubbing brushes on the surface of the Comm and the friction and heating that goes with it .
So brushed motors are a triumph of practical design over physics, that carry a built in handicap with them

 Brushless motors avoid all the problems mentioned above by not having brushes.  (as Amanda correctly said)
Timing is done by computer in the ESC,
It can be (and must be) adjusted to suit the load, speed (and the precession of the equinoxes)
Current doesn't go into the rotor, so there are no sliding contacts or the heat that they make
The coils are energised in sequence with current that actually ramps up and down in something like a sine wave form, so the magnetisation/demagnetisation is progressive rather than sudden.
Shafts are shorter (no Comm!  Have you seen the Comm on a good racing DC motor - it can be as long as the rotor stack) so shafts can be stiffer (or stronger)

Brushless motors have transferred a lot of the mechanical timing and switching into the ESC, where it can be adjusted to neet the excact requirements of the motor in all running conditions  - think of it like a fuel injection system with ECU squirting electrons instead of petrol into the motor.
Brushless motors waste less of the battery power  - I  believe that they will use half the energy to produce the same propulsive power

So we can either:
Go faster on the same current consumption
Use smaller batteries for the same performance
Allow the use of Lead-acid batteries where they would have got hot and bothered before
Fit smaller propulsion systems and retain performance
(almost) eliminate the need for gearing, belt drives etc (except for space reasons, etc)
Run cooler internals in the boat

I'm not in any way against DC motors, I love them; (but I liked Carburettors too, and they have joined the Dodo.)
BL motors are coming - they are capable of doing all our tasks well, once we learn what works best where

Next chapter - Motor numbering - can we learn ANYTHING from it?

Title: Re: Brushless Basics
Post by: roycv on November 06, 2008, 02:50:10 PM
Can I also say keep it coming most instructive and easy to understand.
regards Roy
Title: Re: Brushless Basics
Post by: andrewh on November 06, 2008, 03:23:49 PM
Thanks, Roy

For the first time in my life I have had no cabbages thrown, no disagreement (yet), no death threats and no rabid debate on the precise whichness of the what.

Mayhemmers are not only skillful and helpful, also well-behaved (apart from carruthers little lapse)

I am trying to think ahead, and bridge that gap between theory and what works, which I feel is what all this is about.  Just to lay out the way I am going, I think there is a valid way of looking at our boats to guide motor selection.  New applications and re-motoring may finish up the same or different - even if only because the geometrical constraints may dictate a particular frame size for a replacement.

I have sketched out a matrix which has dimensions of:
size (as length)
aspect ratio - (Springer to destroyer)
displacement / semi-dispacement / planing
None of the above (waterjets, sumbarines, hydrofoils etc)

I can imagine that we can populate this with regions of power/speed/prop size/battery voltage/suggested BL (and brushed motors) to start from
I also intend to crack walnuts with my toes and reduce the proof of fermat's last theorem onto a playing card :}
Title: Re: Brushless Basics
Post by: JayDee on November 06, 2008, 03:48:17 PM


 This has got to be one of the BEST threads on the Forum - - - - EVER !!!

John.  :-))  :-))  :-))
Title: Re: Brushless Basics
Post by: andrewh on November 06, 2008, 04:45:45 PM
Thanks, John for the kind words

I don't remember if you fit aux motors in your gorgeous schooners and yachts, but if you did I am able to place them in this array of parameters I am contemplating - something like this:

Size:  Huge
aspect ratio (ratio of beam to length) large - probably 8:1 (at w/l)
Slipperyness:  very sleek (on a scale of Springer to dolphin they would be 90% of dolphin)
requiired speed (from aux motor)  virtually none (say 1kt  - we actually want water flow over the rudder, not boat speed)
required power - 2 watts (guess assuming about 1/2 amp at 4V)
Prop required - as drag free as possible - Graupner, I think, make a folding prop for just this duty - reasonably large diameter for efficiency
motor - brushed - I would go like a ferret up a drainpipe for a 385  - probably on 4 cells
Motor (brushless) - low KV outrunner - run on 4 cells (good news - this is the very cheapest combo to buy, if you can do without reverse about £15 the lot!
Motor Brushless (homemade) - great news - this requirement is exactly what every CDROM motor is already wound for -howk one out of a CDROM drive  - they are given away freely when dead or old - find the three power wires - connect to a b/l ESC; viola! you have the schooner aux drive motor already! :}
(But brushless hardly required )

I have just been trying to get my head round measuring (in some way) the boundaries of this wide hobby
I am also (being a mech eng) considering a mechanical Brushless ESC! for simple duties and demonstration purposes!
Title: Re: Brushless Basics
Post by: Seaspray on November 09, 2008, 02:33:50 PM
Excellent first class write up,well done andrewh  :-))

Many more like this in this fast moving technology world, to keep us informed

I will be putting this on a C.D. for future references.

Hope your not looking for royalties  Martin Mayhem   

Title: Re: Brushless Basics
Post by: roycv on November 10, 2008, 11:03:05 AM
Hi andrewh, just reading about your low power requirements for a sailing boat.   I used a similar set up (no folding prop) in a sail boat a few years ago that I was restoring.  And if I may suggest an alternative to the folding prop, use a small prop with a big pitch.  I know it sounds wrong but it has less resistance to water flow under sail and, with a low powered motor, may revolve in the water stream.  The low revs makes it quite easy to turn.

The small 30 inch loa sailing fishing boat consumed less than 2 watts and just gave enough speed (for lunch time purposes).  Everything ran off the 4 x nicad 800 mAh batteries, including the sail winch.  I used a standard size 10kgrm servo for the sails with an extended arm attached.

See picture

Regards Roy
Title: Re: Brushless Basics
Post by: andrewh on November 10, 2008, 11:48:05 AM

Beautiful boat, and you are a wonderful person, too.
  Its very warming to know that my logic on power and things relating to the aux power for a (mainly) sailing craft is reasonably borne out in your experience.  Even down to the 4 cell power source (My Thames barge uses a  dead 1/4 scale servo for an ESC, and I changed the motor for a 385 only to get a longer shaft)

I got a little useful information at the Warwick Int'l Exhibition - b/lmotors as applied to waterjets!  Always useful, and the information was precisely what I would have expected if the word waterjet was replaced with "Ducted fan". 
More detail later, but a possibly useful guideline for boaters who may be looking at new or replacement motors for waterjets (and by extension very high speed boats with little spidgy props)
You need revs, I'll rephrase that;  you NEED REVS :}
If your waterjet was designed for say, a 540 motor  - like the Graupner mini, then a B/L inrunner with the same fixing holes would be a good solution.  As we have generally covered,  inrunners are good at revs. 

Water jets require revs - I seem to have heard 25,000 rpm being desirable for the mini-jet so this requires a fairly up-market brushed motor, or a simple inrunner with a high KV.
The boat I was admiring had 2 waterjets, and the  builder had fitted two outrunners - (guess 2222/2 with KV about 2500)  These spin the waterjets at well over 25000rpn on 12V and give "adequate" performance.  Note  - he had made an adaptor plate to adapt the 540 fitting to suit the B/L motor face.

Another chapter on numbers on the stocks - thanks for the warm comments on this spiel
Running through the example on aux power for one of JayDee's beauties I realised that even with my terribly limited boating experience there is a lot in good information about, and I can make good use of Graupner published information to back-calculate prop speeds for useful performance.
And with your help we can build a set of solutions which are likely to work :}
Don't mind me - I had a great weekend
warwick/PT boat quiet and fast/sailed my submarine yacht :D
Title: Re: Brushless Basics
Post by: kiwimodeller on November 10, 2008, 11:38:00 PM
Could you arrange me a night out with Amanda while you are about it? I may learn more about brushless motors or I may learn something else equally as useful. Thanks, Ian.
Title: Re: Brushless Basics
Post by: andrewh on November 12, 2008, 01:12:10 PM
Brushless Basics (BLB)   Chapter 4   Numbers – a guide to the uncharted wastes

I bring good news – there is some rhyme and reason in the numbers which are bandied about in the BL arena!
Even better news is that if you grasp this chapter you may well be more informed than some of the manufacturers – especially if they use their own system to describe motors!

I will dive in with a guided tour of what seems to be the most common system for describing brushless (BL) motors.

BL motors often have a part number or description along the lines of:

Emax 4030/10

(I have taken as an example Lifeboatman Paul’s beautiful Arun so that we have something real to consider - hope that is OK with you , Paul, you are hero to us)

Emax is the manufacturer  - or possibly the brand name
Now comes the good bit!
The numbers mean :
Outside diameter(mm): length (mm)/wind!

40mmx 30mm; 10 (turns)wind

So now we know all there is to know about the motor, because the “wind” is really another way of expressing the KV

I have found this motor on the net and the detailed spec is as follows:

No. Of cells    4-7x Li-Poly    
RPM/V   385    
Max. efficiency    86%    
Max. efficiency current    20- 40 A (>78%)    
No load current / 10 V    2,1 A    
Current capacity    50 A/60s    
Dimensions    40x30 mm    
Shaft diameter    6 mm    
Weight    325g/11.5oz.    
Recommended model weight    3000-6000 g    
Recommended prop without gearbox    13"-16"   

The second line RPM/V of 375 is the same as KV=375, so in this motor (but no other) a 10 turn wind produces 375 RPM/volt
You will see that the voltage is given as 4 to 7 lipo.  That’s 16 to 28Volts (when fully charged) and so the revs at the shaft are between 16 x 375 = 6000 to 28 x 375=10,500 RPM.  Lifeboat Paul uses 12V so he is getting 4500 revs and staggering performance with 75mm x what? Props.

Attempt to calculate the Arun’s speed
(I am going to ask him the pitch, but guessing at 1.5 times the diameter is 127.5 mm pitch, and with a slip of 22% that gives 100mm per rev of forward progress
100 x 4500 is 540000 mm per minute which is 9000mm per second or 9 metres per sec (about 30 feet per sec or a little more than 20MPH) , which is travelling!  I suspect that the props are actually coarser than that so the speed is probably a little faster)

The power used (approx) 
The current range of the motor is 20 to 40 Amps (for good efficiency) and I am going to guess at 20 Amps (because Paul is using Lead –acid cells and I saw no smoke)
So (per motor) 20 amps at 12V is 240 watts motor input power
So the Arun is using twice this (2 motors) or 480 Watts, which is very close to half a Kilowatt!  One horsepower is ¾ Kilowatt so this is getting towards one HP. 
Guessing again that Paul is using 7Ahr lead batteries
If you take 20 Amps out of them they should provide this for 27 minutes* (7 Ahr is 540 Amp minutes so if you take 20 amps they will last 27 minutes)
* but if you read the specs you find that at this sort of current the capacity is less than half of the advertised, so I would expect to see the boat sag a bit after 15 minutes!

Does this help?
I ask quite genuinely because I live calculating, estimating and where necessary guessing engineering units but you may not be so confident.

I HOPE to be able to assemble a basic table which would assemble some of the wide ranges of boat types we make/drive/fly and suggest motor descriptions/props that have a fair probability of making the owner happy (I am very aware that this means different things to different owners)

So from an example (where Paul has already done the selection ) we can reasonably accurately work to the performance expected.

We can do this the other way, too
If we know what we want to achieve – speed, prop RPM, length of run we can work the other way and find a motor that will give us the power, revs, torque and price that we want!

Could you arrange me a night out with Amanda while you are about it? I may learn more about brushless motors or I may learn something else equally as useful. Thanks, Ian.

Sorry Ian, not a chance.  Amanda is helping me with research while the ink fades from her pigtail :}
Title: Re: Brushless Basics
Post by: Garabaldy on November 12, 2008, 03:14:15 PM
Can i ask how 7ah is 540a minutes?  I thought this would be 420 as 7 x 60 = 420.  Im a long way from knowing much but if the 540 is correct how do you calculate it?

besides that confusing point.  Another very informative chapter about brushless motors :-))
Title: Re: Brushless Basics
Post by: andrewh on November 12, 2008, 03:40:35 PM
Peccavi, again <:(

Garabaldy , You are right, of course it should be 7 x 60 or 420 Ampminutes

So the calculated duration should be 420 / 20 minutes or 21 minutes (if the capacity of the battery at this current draw was 7AHr)
(I will edit the post but make the edit visible )

Unfortunately I do the arithmetic seperately while drafting the words, and they are not in the same place at the time I put it into MBM
Sorry - I must check more closely

For fun, while flying indoor planes using 50MAH cells (Sanyo NA50s) we would turn the capacity into ampseconds, cos a KP01 takes 4Amps out of them (4 amps at 2V is about 8 watts - will fly a 30inch Tiggie indoors, freeflight and slowly)
bedecked in sackcloth
Title: Re: Brushless Basics
Post by: roycv on November 12, 2008, 06:30:55 PM
hi, the amp hour rating of batteries varies, I believe gel cells are rated at the 20 hour rate, that is the various combniations mentioned above are good for a discharge over 20 hours.  As said above high discharge rates have a lower battery efficiency.

Lead acid Cyclon cells are like Ni-cads and are rated at the 5 hour rate.  So the numbers are good at a higher discharge rate.  So may show up in a longer run time etc.

regards Roy
Title: Re: Brushless Basics
Post by: roycv on November 14, 2008, 03:11:18 PM
Hi Andrewh, I bought a brushless motor off the internet via HK about a year ago.  It is from RC Smart and is an XSpeed 2900 ( I think that is 2900 revs / volt)  with a 5.5 : 1 gearbox attached, well they are screwed together.  I have a single direction ESC with it, this is up to 40 amps and 14 cells but none the less very small.  The motor was rated at a maximum of 20 amps.  All for £6.50 sound cheap but p&p was £12!!!
I think it was meant to be part of a helicopter drive.

The motor is 2cm dia. and 3cm long, not much bigger than a servo motor!
I have adapted it to take a UJ coupling.  When running in the hand so to speak on a 30 mm prop in a sink of water the power was quite frightening!

It was not happy at 6 volts so I upped it and it ran consistently.

Actual speed control was not very good, top speed was fine and a bit slower OK but then it would stop and wait before I could get  back to top speed.  Trying to give the prop a turn to encourage the motor was futile and dangerous.

I was thinking of utilising the non effective part of the Tx. stick movement to control a reversing switch via a relay.  I have the circuits already made up.

I would much prefer a direct drive motor, but providing the rather small teeth on the gears can take it I shall have to go with what I have got.
Regards Roy.

Title: Re: Brushless Basics
Post by: andrewh on November 14, 2008, 04:51:09 PM
Roy,  I will run round the little gem that you have soon - looking on the website thay have two motors at 2900Kv - a inrunner and an outrunner, but the gearbox suggests an inrunner - could you please elucidate? 

BLB Chapter 5

Well I’m getting a little clearer as I write and wresearch, I trust that you travel, like me, with hope.

A few bits of housekeeping before the brain dump:
Before my Hellkitten
got painted and bedecked with military store she was a Ricky Webb plan built to test a homemade brushless motor
It would be pusillanimous of me to write a spiel and not put my magnets where my mouth is :}
 so I will make a reduced version (faster) and share the build, outfitting, homemade reversing device and all the power components with you – if even to demonstrate that we can ALL dive in and do this!  I plan to post this (or at least the brushless power train details ) on a separate post in this area. [But will be guided by Martin, as ever]

BL motors – the real range possible - now
There is indeed an infinite range of BL motors available (I have a minidisc motor which weighs a gram) but while contemplating 1/350 Yamatos I realised that nearly all the smaller motors are outrunners (which, you remember, tend to be large diameter and short length)
The smallest diameter inrunner (stationary case) motors available are the types that can be interchanged with GWS IPS motors which are round-case brushed motors of 12mm diameter.  There are whole families of these motors all 12mm diameter with the same shaft size as the IPS motor (and for what it is worth the whole Mabuchi FK050 family)
This is good news for plastic magic people – there are even short case versions for less weight.
But all of them are very high KV, high revving motors, so would need either:
In the outrunner style BL motors go VERY small, but as I have said usually of a “pancake” format.  They will produce good torque (for the power) because of the diameter, but may not fit so easily in small warship hulls, etc

Numbers 3 – Identity parade

Right, we have had a swift shufti at a quite common numbering system which describes the motor fairly well, and gives us a clue even to the KV of the motor.
Before passing onwards it is worth saying that:

This numbering system is used in both inrunners and outrunners.
Inrunners probably only have a choice of two different lengths for any given can size, with 3 or 4 different winds (KV) in each length.
Outrunners tend to be made in about 6 different diameters, pretty much the same as other manufacturers  (for example 22, 28.  Each diameter is made in about three lengths of rotor, and each of these is made in several winds

Winds – definition and waffle
Electric motors of most normal types have components wound with wire.  If the components are “inside” the motor there is a limited space, so the windings have to come as close as possible to filling the space for them. See picture of stator core to see the space available for wire 
If you wind with very thin wire –
A) you will get lots of turns in the space
B) You will have almost perfectly have filled the space available – not much wasted gaps between the round wires
C) you will have made a Brushless stator with low KV and/or high torque

Conversely if you wind with THICK wire
A)   You will get only a few turns on
B)   There will be lots or air gaps between the turns of wire (cos its round)
C)   You have made a Rat-motor with High KV which will scream at low voltages

There is a trick for a thick wire winding which instead of using one thick wire with the desired cross-sectional area you use instead two (or 3 or 4) thinner wires together which make your desired area (and will therefore carry the same current). 
•   The thinner wires improve B above – they pack together better, they are MUCH easier to physically do. 
•   You will probably gain enough space to get one more turn on.
•   There is more insulation on the multiple wire than on a single wire – so it is not quite as electrically elegant

So you will see that low winds (which are not exactly the number of turns of wire on a pole, but is related to that) means:

Why are there different winds and KV?

Sorry, its us aeromodellers.  Some of us want to turn a large propeller slowly (2000RPM), and some people want to drive a ducted fan at 30,000 RPM.  We both want to use much the same battery pack (voltage) so there immediately was a requirement for different winds.

Similarly the car/buggy crowd divide into those who want to kill the battery in 5 minutes and want blinding speed – the buggy racers
And the rock-crawlers who power each of their wheels and desire to crawl at stump-pulling speed all day.
Boaties also divide similarly and the broad church includes paddlers and puffer drivers who want a few RPM with stonking torque to the racers and water-jet folk who need revs, revs and more revs, and are prepared to raise the voltage (now we have LiPos) to get it.

I will not be able to add pictures into this today – but I will post it now and either edit later or add them with commentary later


Title: Re: Brushless Basics
Post by: roycv on November 17, 2008, 02:32:15 PM
Hi Andrewh, my motor is an inrunner (stationary case).
Keep it coming so far its better than the 'soaps', which I do not always understand!
regards Roy
Title: Re: Brushless Basics
Post by: Martin [Admin] on November 17, 2008, 03:58:46 PM

Just as a side point (don't know if your coming on to this later Andrew) but say I want a "slow" motor for, say, a tug, what motor / information/ windings should I be looking for?

The couple of speed controllers I've tried seem very reluctant to run at slow speeds. Now I guess this is because the motors
I've tested are "sensorless", but how what minimum speed should I expect from a nonsensored or sensorless brushless motor?

(NB.. Sonsored Brushlees Motors:
Most servos have a feedback circuit so it 'knows' where the "arm" is, so to some brushless motors have feedback circuits so it knows
the actual RPM and can correct it accordingly. Therefore I assume that "normal" ie. cheap brushless motors send out the controll pluses
and just hopes the motor keeps up! I therefore ALSO assume that controlling bushless motors at slow speed is a lot more involved
ie, expensive - Is that sort of correct? )

Title: Re: Brushless Basics
Post by: andrewh on November 17, 2008, 04:29:18 PM

Yes, yes, certainly and probably.
And in that order, I think :}

You observation about the speed happiness of the motors is similar to Roy's observation, and FWIW I suspect that the cause of the instability is more to do with load than speed.  There is a whole "map" of voltage, loads, speeds which the ESC tries to match appropriately  - and the more expensive speed controllers are programmable over a wide range to better match the speeds, accelerations of the specific motor on the end of the wires.

As you surmise sensored motors give a specific timing signal to the controller, sensorless ESCs are a little more sophisticated than guessing - they listen to the pulses received from the motor (acting as a generator) to know when and where to fire.
I believed until a week ago what sensored BL motors had gone to join the dodo and VHS, then found a web page
of dozens of BL motors - all sensored, all buggy type inrunners (540 size or 05 in US parlance).  I believe it is a current chart - perhaps someone who hurrls buggys can tell us?

I do plan, Martin, to do a chapter on "Brushless ESCs for Fun and Prophet".

For tug/paddle/slow speed we should be looking for: 

Large diameters - they generally run more slowly
Low KV - the lowest in the range
High wind numbers - if there is an option of a 10, 15, 18 and 27 you need the 27
run it on low voltages (to slow it down)
Gear it if you must

Brushless demonstrator will be a very small (12 inch hard) chine boat with speed 400 racing prop and shaft .  The hull plans are available for free download, and she will be made of Styrene (for speed).  The rudder will probably have to poke out the back a long way - so that will be a learning experience :}
Title: Re: Brushless Basics
Post by: SteamboatPhil on November 17, 2008, 09:37:29 PM
PLease do keep it coming, its now starting to take the mystrey out of it all for me. It will be my intention to fit a brushless to an old 30" semi multi hull I have, and now I'm starting to get to grips with it all, many thanks.  :-))
Title: Re: Brushless Basics
Post by: andrewh on November 18, 2008, 01:35:51 PM
BL interlude

A moment of orientation to see where we are and where we are going.

I stuck in chapter 1 a listette of topics I aimed to cover - many of these are still valid, and several of you have been reading ahead and anticipated the issues - this is great, since it all actually blends together anyway.

“Chapters” I have in mind to follow on with include: (but are not limited to)

1.   Inrunners/Outrunners differences, similarities
2.   Matching an existing motor
3.   Gearboxes, belt drives, etc
4.   Kv for fun and profit
5.   Why would I want to change to a brushless?
6.   Boat speed, motor revs, voltage?
7.   Mounting the beasts
8.   Reversing – how do I do this
9.   Speed control
10.   Why would I be interested in 4-D flying??

I feel that of these I have romped through 1 and 4, with passing reference to 5 and 6

One or two more topics have grown organically as the weeks have progressed:
a)  Roy's 2900KV inrunner/gearbox
b)  Andrew's brushless demonstrator
c)  What I am calling the get-close BL table
d)  Time was short when I last posted a chapter, and the intended illustrations did not get posted (I had not had time to load them into photobucket)

Time is short again now - but here is a picture that illustrates how an outrunner is wound, with the size of the winding spaces - it also illustrates that therer are 9 poles on the stator (usually 12 magnets round the rotor); and the poles are wound in threes, with one length of wire winding three poles.  Funnily enough these are 3-phase machines :} 

Your homework is to Imagine doing this winding with coat-hanger wire :}

Roy's 2900KV inrunner.
Sorry, I keep finding and losing the URL - it has now vanished again
Roy - what you have is a replacement for a GWS geared flight system - even down to the gearbox.  The motor is, from memory 30mm diameter and 35mmm long with a middling KV of 2900RPM/volt
So the motor is effectively a Speed 400 replacement - I'll bet it has the same fixing holes
BUT it handles 16 amps at up to 18Volts, so if we calculate at 12V this is 12 x 16 Watts or 192 watts
A speed 400 has a max of 10A at say 7V or 70 watts
So this little BL is capable of handling approx three times the power of a speed 400, and will last longer, too (at 10Amps you are offending a Speed 400 quite well, and the brushes will soon let you know)
A S 400 7.2 has a KV of 2250 so this is a direct replacement for a S400, and will turn the prop rather faster!

If a S400 racer is a little overpropped with a Graupner 29mm carbon prop - this motor would be very happy with it, and might like a little more  diameter if used with direct drive

Geared it will turn a much bigger prop - I don't know what you used for your sink tests, but I would start in the 40mm to 45 mm range (same as GGs 2;1 geared 540s)  Remember that with the gear the KV reduces to 2900/5.5 or 527revs/volt so on 12 volts you will have 6300 revs at the prop - this suggests to me a fairly large or coarse prop :}

Go for it, Roy; and pictures, please
reversing - I am also using a aero ESC, so I am going to make up a reversing gadget using a changeover switch - it will be posted HERE with the smoke in sharp focus.
The stuttering is probably a function of load - the motor is trying to run too fast, and losing count of its fingers - try adding load - either a bigger prop, or an air propellor, or FLJs fingers and see if that steadies things up

Your homework for tonight  - think not more than one paragraph on "4-D flying, and why would Andrew be yorping about it"


Title: Re: Brushless Basics
Post by: Garabaldy on November 18, 2008, 03:31:48 PM
I understand that for converting a tug to brushless requires a motor with a lower kv rating to lower keep the revs low and also to produce the required torque.  My question is - Is it possible to do this as economicly as with brushed motors?  For instance i could buy 2 graupner 900bb torques and a action twin speed controller (P94?) for £110 or there abouts.  All the lower KV motors seem to be really expensive.  Or much more than £30-£40.  Do you think a motor with a 600KV running on 6v swinging a say 100mm would be suitable?
Title: Re: Brushless Basics
Post by: andrewh on November 18, 2008, 04:59:58 PM

I don't know the exact answer to your question, but am happy to give it some thought:

Do we know what revs you would like, or any more information about the prop?
I know (qualititively ) that tugs need low revs, big props, etc, but do we know any numbers?

Generally the lowest KV motors are the biggest in diameter and power, hence the most expensive.  Within a given size of outrunner the lowest KV motor is the easiest to make (easiest winding) and the most efficient (most copper on the poles)

900BB Torque
Eureka - I recognise that motor - and so does anyone with a high-class 12V electric drill (not DeWalt)  it has a KV of 6500/12 or 541RPM/volt
(which is very similar to the  Roy's geared inrunner at 527 KV)

I will have a scout round and see what seems like a good bet in outrunners. 
I'm working on the assumption that we are aiming at a direct drive to the prop, and it may be that the right direct drive motor might be an LRK type.

If gearing is a possible thought, then using say a MFA Olympus belt drive (3.3 to 1) and a 1500KV outrunner around

Looking through an ebay range of direct drive motors I came across this one.  Not sure why you say the Low KV motors are expensive - even though this is a Oz site,  71$Au is pretty cheap - the KV is 800, on 3 Lipo cells, so running this around 7 to 10 Volts (or 12) would, I think, memorably overpower your tug

Please don't dive in with the possibility of me beng wrong, and you being broke - have a look at the specs of the 900BBtorque and this motor

more tomorrw

Title: Re: Brushless Basics
Post by: andrewh on November 20, 2008, 01:09:54 PM
Sorry, Chaps; I lost a complete post yesterday - it must be somewhere in virtual space :}

While researching i have found some good resources (or at least better than nowt)

First up a motocalc listing of very large numbers of motors - brushed and brushless

This is very useful as it includes hundreds of the familiar Graupner and Robbe motors, and lot of Mabuchi standard winds and sizes - and gives the essential KV and efficiency information.  Hundreds of BL motors are listed, too, so it might be a help in finding good replacements.

While hunting for low KV tug motors I found a goldmine, as well as what I was seeking :}
This is a table of the Scorpion range of BL motors.  They folllow the size numbering convention we discovered earlier, but this is a comparison table with many other manufacturers BL motors - including AXI which are very good, but only their mother can work anything out from their model numbers
Scorpion motors are offered as kits (so are GoBrushless and Komodo) - suggest you have a look at that page, too

betterer and betterer - there is a complete BL power/performance calculator

No doubt this works best for scorpion motors, but would probably give a fairly close answer for another of the same dimensions and wind

These two are both on the Micron RC site - they are card-carrying good guys (no relationship - just satisfied customer) - yopu might like the have a look at the micro-motors, too, and imagine a micro-hydroplane with a 4gm brushless going like micro-stink :}

More soon including more practival ansrws for Garabaldy and the Tug

I have started a thread nearby on my brushless demonstrator - and made the boat this morning (30 mins so far)
This is my (new) cutting mat with 540 buggy motor (for scale) with my homemade brushless motor (blue cylinder), ESC and a CDROM motor as salvaged out of a computer CD drive.

more as it happens - contributions welcome

Title: Re: Brushless Basics
Post by: muduck on November 26, 2008, 12:59:48 PM
A thread in the nick "O" time...great stuff, waiting for more info to come.
I have a Mountfleet "Cruiser" with a Proteus steam plant. The combo is perfect, but I need the engine for another project, & was wondering how to go about utilizing brushless tech. I'ts still a bit of a mystery, & I keep re reading what you have written, but then it's probably why I love my Four Strokes on the planes, I know exactly what size I need for which plane...
Title: Re: Brushless Basics
Post by: muduck on November 27, 2008, 11:00:39 AM
While you lot in the NH were shivering around the fire, I spent(not wasted) the 30C day looking for something that may power the Cruiser with her 4 bladed70 Rivabo prop.
Any thoughts?
Title: Re: Brushless Basics
Post by: Garabaldy on November 27, 2008, 12:39:43 PM
i have the 35amp version of the seaking speed controller.  I have 2of them in my fireboat and they are good.  Once you get them set up.  The most iriitateing thing with them is when you want to reverse the motor you have to pull the throttle stick right back then set it back to zero then pull it back again to reverse the motor.  the manual calls it  "double click" (
Title: Re: Brushless Basics
Post by: Martin [Admin] on November 27, 2008, 02:22:46 PM
Brushless sets on ebay:
RC Ship 2100 KV Water-Cool Brushless Motor & 60A ESC.

RC Ship 3600 KV Water-Cool Brushless Motor & 60A ESC

Well clean the topic up later Andy...
Title: Re: Brushless Basics
Post by: lifeboatpaul on December 07, 2008, 01:37:01 PM
I have just been reading this thread- Ohh I do love the part in Andrewh`s reply concerning the BL
Title: Re: Brushless Basics
Post by: lifeboatpaul on December 07, 2008, 01:43:29 PM
this I was should have gone before the last post but it I hitthe enter key and posted halfway through

(I have taken as an example Lifeboatman Paul’s beautiful Arun so that we have something real to consider - hope that is OK with you , Paul, you are hero to us)
P/s just to clarify I use the motors on 24v ( 2x 7ah lead acids) and both the ESC`S together on a Y lead ( the bec`s seem to be OK working together)

Paul - ( the hero?)
Title: Re: Brushless Basics
Post by: andrewh on December 07, 2008, 04:01:13 PM

Brushless speed controllers, or “How To Feed Your Brushless Motor”

Where to start?
I have been wondering where and how to get into this topic - and the obvious place seems to be at the beginning, with the basics :}

What the motor needs
We know that these are 3-phase AC motors, so we need to feed them a diet of just exactly that.  Speed comes from the frequency with which we feed the motor current in each phase (it is a variable-frequency alternating current)

I have failed to find any useful pictures of 3-phase supply, so I have generated some sketches using my CAD package (Pencildraffy1949).  I do not claim that these are perfect, or perfectly reflects what is actually happening – they are the way I visualise what is going on, and are, I hope helpful in imagining the process.

Fig 1 shows 3-phase AC - as it is generated for the mains - with each phase a nice smooth sine wave  I have called the phases 1 ,2 and 3,

Fig 2 shows the simplest and nastiest wave form which would rotate a BL motor - it is completely or nearly square and the sharp corners will make for noisy and rough running

Fig 3 is an attempt to show what is actually generated by the ESC - it approximates to a sine wave, but built from square, but narrow pulses.  The gapa and square enges are sufficiently narrow for the motor to run through them without much noise or mechanical stress.  There are, of course three phases, all generating the same kind of wave-form, but staggered by 1/3rd of a revolution

What I cannot show is the timing, which varies with speed and load, and the type of motor - depending on the speed Controller

More soon - reversing, and a BFO


Title: Re: Brushless Basics
Post by: andrewh on December 08, 2008, 12:57:41 PM
While writing (indefatigably) late last night i managed to lose the entire spiel on reversing and reversability, so here is again.


To reverse a Brushed (DC) motor you reverse the polarity of wires to the motor, and (ignoring differences of timing) it will run happily in the other direction. 
To do this under radio control requires an output on the ESC which works the other way round, electrically, usually arranged as an h-bridge.
FETs to run the opposite polarity are harder to come by and more expensive, which is why marine controllers are much more expensive per amp of output than aircraft controllers (where reverse is seldom called for, and when it is it isn't done that way :})

Reversing a BL motor is actually very much simpler - we just have to reverse the Sequence of the pulses in the three phases we are feeding it.  This is not a matter of polarity, since each of the phases is AC anyway.  Its really a software matter, since all (probably) of the BL ESCs are microprocessor controlled,  the output stages just have to "fire" in the reverse order and Bob will be your avuncular relative.

The phase sequence

I am going to call the phases (wires) A B and C
To rotate forwards the ESC needs to feed the phases with pulses of voltage in the order:
     A B C A B C A B C A B C A B C A B C A B C A B C A B C ........
If we want the motor to run in the other direction we need to send the phases in the reverse order
C B A C B A C B A C B A C B A C B A C B A C B A C B A.....

These are in fact the only two possible permutations of order with three phases , and if you compare them with hawk eyes (starting at any phase letter) you will see that one direction is ABC and the other ACB - in other words two of the wires are reversed.

Alleluia!  This is exactly the same switching that reverses a DC (brushed) motor! 
2 wires  - change them over to reverse
So I did

Two small microswitches are glued side by side and wired as shown.  I use 2mm gold connectors, so they are designed to fit into my motor/ESC connections with appropriate male and female connectors.

Does it work?  Serpently it does - also works on a DC motor too.
The two microswitches are stuck on top of a servo and the plungers are operated together by a lump fitted to the servo arm so that they depress (together) at one end of the servo travel

You can do exactly the same thing with a DPST or DPDT switch operated by a servo (but do make sure that the toggle action can toggle freely)

Incidentally this little switcher is simple and suitable for a bowthruster made from a windscreen wash motor if anyone is interested.

I have used a another channel to operate this reversing switch, but it must be possible to do it elegantly with the same channel as the ESC - (or possibly brutally)  I am going to consult experts about this possibility, and will relay you anything interesting that comes out of it.
Why do this?  Well, 15A brushless ESCs are available for prices around a fiver :}

In case you missed it
certainly the fastest and silliest Razor in the world

Next chapter;  4-d flying and the boating community

Title: Re: Brushless Basics
Post by: andrewh on December 08, 2008, 01:17:12 PM

Thanks for posting - your lifeboat is an impressive lesson to us all, and the detail you had included in telling us about it was so complete that it illustrated the whole type of large, planing boat beautifully.  Thanks

Thanks for the battery details, too - I had been rather concerned about the currents at 12V, and meant to ask you if those were interior running lights or the batteries glowing :}

Gentle readers  - you will have gathered by now that my (model) boating knowledge is not extensive.  You-all know much more that I do about the boats you specialise in.  Some of these emphasise performance, but length of run and the use of lead-acid batteries also seem to figure large in the design reqirements.

I still wish to set out a broad chart with first-cut Brushless motor suggestions for as wide a range of boat-types as possible
even Henry:
contributions welcome
Title: Re: Brushless Basics
Post by: roycv on December 08, 2008, 03:06:12 PM
Hi Andrew, very much enjoying the thread.
I expect that this is a very silly question, but here goes!
With a brushed motor if the load is increased generally the motor slows down.  What happens with a brushless motor?  I would expect that it would try to rotate to follow the variable AC input frequency.  If you start slowly and the motor follows, fine, but as the load increases with rpm what happens if the load is too great?  Does the motor stop, get hot or protest in some other way? 

many regards Roy
Title: Re: Brushless Basics
Post by: andrewh on December 09, 2008, 08:40:51 AM
I expect that this is a very silly question, but here goes!
With a brushed motor if the load is increased generally the motor slows down.  What happens with a brushless motor?  I would expect that it would try to rotate to follow the variable AC input frequency.  If you start slowly and the motor follows, fine, but as the load increases with rpm what happens if the load is too great?  Does the motor stop, get hot or protest in some other way? 

many regards Roy

There are no sillly questions, and this is a very wise one :}
I don't know the full answer, but am happy to explore it with you.

Some of the answer lies in the fact that a DC motor can run without the ESC, but it is not possible to consider a BL motor without its ESC. 

Both motors have the same characteristic of generating back EMF as they rotate - a DC motor has a VERY low resistance if you measure it statically - so it takes a huge current at rest (the start-up current). 
As soon as it is rotating  it also generates, and this has the effect of increasing the apparent resistance and reducing the running current.
All well and good, until you put your finger in the propellor!
(I (and my fingers) are more used to aircraft props, but the same applies to water props)
The motors slows down, the back EMF reduces, current increase and the second blade hits you a good one! - I have been cut by the 4" prop on a KP01 motor (2 volts, 4 Amps - an 8watt motor!)

This same process happens generally for both Brushed and brushless motors - now we need to consider what is happening with the BL and its ESC.
It is trying, as you say, to run at the speed commanded by the throttle stick - the ESC is feeding the motor a rate of rotation (of the phases) that does this, and the motor will, if it can, exactly follow this.
Now if the load increases suddenly - say picking up a nice length of fishing line in the prop :} - what happens?
Well several things at the same time - the "slowing down" habit described above will happen - current goes up to try and compensate for the slowing.
Also the ESC will detect the slowing (it listens as well as talking to the motor) and it will adjust its frequency to suit what the motor is actually doing - and try to restore the set speed.  So it will if it can.

So the basic answer to your question , Roy, is yes, pretty much!
The basic characteristics of "self regulation" will be similar, the second blade will still hurt badly, and even more - there is an ESC with its fast (but tiny) brain trying to do all it can to restore the motor to its original, set speed.  It should not overheat, since the ESC will not feed it more than the ESC can supply (most ESCs seem to be temperature -protected)

Title: Re: Brushless Basics
Post by: andrewh on December 09, 2008, 01:43:34 PM
I'm a (mature) mechanical engineer, and occasionally prone to bursts of the blindingly obvious.
 I'm also Scottish by birth and a little financially "aware"

I can tell that you-all  out there are electronic experts, but me, I just like to understand what is (or should be) going on in those boxes with electric strings going everywhere.

I am going to make, in the best Mayhem tradition, a brushless motor-driver
It will (OK, should) drive a BL motor, and in both directions.  Cost is expected to be approx GBP 6.00  if I buy the critical parts new
It will be visible, understandable and yes, fairly silly

I should occasionally listen to myself
I have thought, said and written that forwards-only BL ESCs are cheap and readily available - about a fiver
my reversing switch cost nowt - because I salvage microswitches from alll household gadgets before they are thrown away, but if you bought the microswitches and servo it would cost a lot more than a second ESC

Now all I need is a way to operate one ESC for forwards and the other for going astern, and both at once for the dramatic , but unique, fireboat impression :}


Title: Re: Brushless Basics
Post by: roycv on December 09, 2008, 02:12:34 PM
Hi Andrew thanks for taking the time to explain, please carry on with the information.  Look forward to seeing yourBL ESC, the commercial reversing esc's seem very expensive by comparison.
regards Roy
Title: Re: Brushless Basics
Post by: andrewh on December 09, 2008, 02:34:23 PM
Thanks, Roy

I hope I carefully didn't say ESC :}  I can't do E to this extent - thats what friends are for

But yes, motor driver and MSC it should be

My hope is that it will stimulate you or someone to say "Oh, I see now , all is need is a phase sequencer and deflocculator with an FET output"  and produce the ultimate marine reversing ESC

Title: Re: Brushless Basics
Post by: roycv on December 09, 2008, 10:57:39 PM
Hi Andrew  I used to know what a suppressor triggered phantastron was.
I found I could live life with little reference to it so it had to go.  I'm OK with FET's but I used to use emitter followers.
regards Roy
Title: Re: Brushless Basics
Post by: andrewh on December 10, 2008, 07:37:05 AM
I just try and avoid SED*s, unless they are free or very cheap

*Smoke emitting Diodes

Title: Re: Brushless Basics
Post by: andrewh on December 19, 2008, 04:20:02 PM
Nearly Christmas, so seasons greetings to all readers, or reader as the case may be.

I am fortunate that Amanda still puts my Zimmer frame through the carwash. 
If it helps you with visualisation she has a strong resemblance to Samantha the scorer on "I'm sorry I havn't a Clue"

Where are we?

A)      I threatened you with 4-D.  I hope you have done the homework (but at this season of goodwill I can overlook the claim that the dog ate your Google button.)

What on earth, I hear you ask, is 4-D?  well its a branch of indoor RC flying  which involves the plane not only flying and hovering forwards - but flying and hovering BACKWARDS and nose-down :} as well
Well its a hobby for a young, rich person since  the walls, floor and roof approach from both ahead and behind the plane, but it may have some interest to boat-builders and users because the trick is done, not by reversing the motor (always brushless) but by reversing the prop blades!

So all 4-D motors have hollow shafts, and you can buy hollow shafts for most of the smaller brushless motors. 
This leads me to think about reversible pitch props for brushless boats. 
What we generally want is efficient progress forwards and some sort of reverse.  Not the same speed and power, but just some reverse motion
Thinks:  4-D props - helicopter tail rotors, swashplates - there is a lot of hardware out there that could make the linkages work easily. 
All we need is a strong, reliable variable (and reversible) pitch prop

B)  BL twins

The written wisdom is that you need one brushless ESC per motor. 
There are many recorded and successful cases where that is not essential and twin motors are run off one BL ESC.
While I'm not sure if anybody knows the whole answer, it is certain that for this to happen:
The motors must be identical (same model, same manufacturer)
The propellors must be identical - in each case I have heard of these have been Gunther props
The ESCs have been of several sorts, both cheap and Castle type.

None of the flyers (they were all flyers) had any problem with getting it to happen, or changed the program of the ESC to suit.
Flyers are generally using equipment MUCH harder than boat modellers (we have to to get into the air) so the motors and ESC were running close to their rated power.   
It should be very much easier for boat modellers to get two motors to run off one ESC since the speeds and loads are generally lighter, and its not too difficult to get near-identical props.

DISCLAIMER - I can see no way in which trying this could damage either the motors or ESC, but I have not done it myself (home-made motors - none identical). 
If you try it do so carefully, it may well not work and you do so at your risk
(I have subsequently done a search which confiirms basically what I said above - it often works .  There was one mention from an owner that he ruined two motors and damaged the ESC)

That's it for now - I am going to update the BL test boat thread now
I aim in the near future to go back over the thread and pick up any loose ends and try and tie them off (or encourage them to slip BL motors into boats and tell us about it)


Title: Re: Brushless Basics
Post by: Bluechrisp on December 28, 2008, 11:03:12 PM
Hello Andrew,

A great thread, now my heads hurting, I fairly new to model boating, I would like to update a Sea commander from a Graupner 600 on a 6v/7.2 batt to a brushless set up, the boat is 34 in long weighting up to 6 kilos. speed about 2-3 mph.

I had a look at a few but not sure where to go for, on a old woodern boat.  any ideas.  :-))


Title: Re: Brushless Basics
Post by: andrewh on January 06, 2009, 04:04:39 PM
Hi, Chris
Sorry for the delay in replying - family things over Christmas and the New Year have got in the way
Reply very soon

Ths back cover of the UK comics  carry adverts from Mtronics which include the Hydra 15  brushless motor and ESC package for about GBP50. 
This combo doesn't appear visibly on their website, altho the ESC does (with its big brother the Hydra30) so we don't know what the BL motor is - it LOOKS like a 28/20 and they do say it fits onto a 480 (from memory) mounting. The 15 and 30 BTW refer to Amps continuous but there is very little further info

Here is the question - has anyone ever seen the combo, or bought one, or seen one in a boat or on the water?
I have enquired of Mtronics for more details, and will pass them on as received
If offered a unit to test I might hesitate for picoseconds before replying :}
Title: Re: Brushless Basics
Post by: andrewh on January 07, 2009, 01:28:33 PM

Thanks for your query - Sea Commander, eh?
I don't know the answer, but let's see if we can work towards it :}
We have a tree-wood boat, quite heavy (6KG) 34inches by 10+inches and a good planing shape
You are powering it with a a Speed 600 , buggy pack, unknown prop and get 2-3mph

First some questions
TIA for answers

Ways to size a BL motor:
1)   Go to the Mayhem BL database and find the closest to boat and performance option (still lies in the future!)
2)   See what we can calculate from the existing power system
3)   Ask stavros
4)   see if there is anything similar in Weeds spreadsheet

We can't yet do (1), so lets have a go at the rest
2) existing power system
S600 with bugggy pack.  I will assume direct drive.  2 to 3 mph is displacement speed (not planing).  I have no information on current draw, duration or prop so let's  assume about 35mm prop, current draw of 5A (this is a 20 to 30 Amp motor in aircraft).  If the battery pack is 2000maH (guess) thats 2Amp for an hour, or 4 amps for 1/2 hour so 5 amps would run for about 25 minutes
5 amps at 6 V is 30 watts (assuming 6-cell pack)
If the prop is 35mm diameter with a pitch of about 40mm it travels 40mm per rev (ignoring slip)
3mph is close to 1.5m/sec or 1500mm/sec
it takes 37.5 (1500/40) revs to move this far, and this is per sec
37.5 revs/sec is 2250 revs/min - which seems to be FAR too low  - under light load I would expect even the ECO motor to be turning about 10Krevs
BUT - I have also found an SC which is powered by an OS30 or 35, and the action pics show it resolutely ploughing through the water (not over it).  This is what I call a stunt motor - long-stroke workhorse which would probably be running 7 to 8000 rpm under load
This boat has a 55mm prop
if the OS produces maybe 1/4 HP (187watts) (it is a slogging motor with a long, small diameter  exhaust) the boat appears to be moving at jogging pace - maybe 5 to 8 Mph, but certainly not near the plane.

3) Stavros, I know has a large aeroKits boat (prolly Huntsman), and a cunning plan to give it a surprise, large brushless and blinding performance
When last we spoke he was plotting a 800watt motor and 75mm prop.  It seems likely therefore that Lllllyn Padarn will be crossed with the boat only touching the water a couple of times
We reckoned that the power train out of half a 1/10 lifeboat sounded about right (for blinding performance)

4) Weed's spreadsheet
I'm going to have a look when I can get it to load - we will come back to that

So here we are - what have we learned?
Power aim is more than 30Watts , more than 180watts if we want her up on the plane (once planing the power requirement comes right down, but you need raw power to get the hull out of the watter)
We don't know how much room there is for prop diameter, but the bigger the diameter the more "grip" it has on the water, and the less slip and wastage of power
The two probable S600 motors have KVs of 2526 (S600 7.2V) and 1583 (S600 7.2V Eco) so we need to match this IF THE PROP HAS TO REMAIN.  It would be better to aim for a larger prop and BL motor with medium KV (say 1000 to 1500)

So before Chris replies my thoughts are going down the lines of
 - this is 350 watts and would need feeding with up to 12 cells - could be 2 cheap buggy packs.  KV is 1100 so it would need or like a bigger prop.  Max current is 30 A so a 30 to 50 A brushless ESC would be needed

Contributions welcome
I have not been able to open the Weeds spreadsheet today


Title: Re: Brushless Basics
Post by: Bluechrisp on January 10, 2009, 12:30:26 AM
Hi Andrew,
The SC does plane for the first 5 minutes, even on a 6V SLA then reverts to  normal as the power goes, I have a 37.5mm P prop 2 blade plastic, could take a 50mm prop, the 600 engine is 6V. I would like it to go faster, even leap out of the water maybe  :o well nearly, did see a 700 series water cooled, to big mmmm   %% any help would be great, I'm still trying to get to grips how great these brushless motors are....  :-))

Title: Re: Brushless Basics
Post by: EJL on January 11, 2009, 01:58:02 PM
If I can offer any help ask away. I run high power racing boats/ scale racing boats and all my boatss have brushlkess motors in them.(except the gas turbine)

I own Mega's and  Aveox to name but two.........  Numerous makes of speed controllers.

Some of you will remember me from my days writing about fast electrics and related boats for Marine Modelling Magazine (12 years).

Andrew has covered the technology I can cover the application.  I am a little out of touch with Lipo technology having stuck with Sub C cells but will be catching up soon.

Ernie Lazenby
Title: Re: Brushless Basics
Post by: andrewh on January 12, 2009, 09:52:33 AM
You are a scholar and a gentleman, Sir :-))
Your offer of help is enormously welcome and appreciated - your experience will be very valuable.

Gentle readers, the names Aveox and Mega are talismans in the brushless pantheon (to mix a Monday metaphor). 
Aveox were one of the companies which pioneered brushless motors and controllers in the early 90s - first with sensored units, later sensorless.  I well remember the first Aveox Brushless which was made to power A LARGE (1/3 scale?) Fokker triplane and direct drove a prop around 36  inch dia!  Unheard of for direct drive at the time - IC or electric.

 Mega are European, made stonking brushed motors, specialising in direct drive and competition units of extremely high quality.  When Mega introduced BL motors they followed the same mantra and made robust creations which are found in competitive FE boats as well as aircraft (F5E, I seem to remember) and (no doubt) cars.

Ernie - biggest gap in our knowledge is probably the performance of props, what RPM they do, what power they absorb at what revs.  Do you know of any resource where such things can be found or deduced?


[edited - speling]

Title: Re: Brushless Basics
Post by: andrewh on January 12, 2009, 10:27:53 AM

Thanks for the reply , your setup is doing well to get a large boat like this on the plane even for the first 5 minutes of the run :}
I have not come across a 6V S600 before, and your prop sounds about right for the performance you are seeing.  I'm running a S600 7.2 eco with 35mm prop in my PT boat - much smaller, lighter and narower, and it planes for the whole of the battery.

However, Volts are King!  If you can, try your SC with more volts!  Beg borrow or  acquire nicad or nimh packs with 7, 8 or more cells, and see what happens.  With modest load the motor will be happy at higher voltages, but the current drawn rises too, with voltage so you should see more vivid performance, but maybe for a more limited time.
Is she planing "flat" or rather bow-up?  If the latter can you get the bow down with weights moved forwards or maybe adjustable trim tabs.  This cuts the hydro drag enormously and will increase both the speed and duration.

I will see what can be calculated at lunch time

Title: Re: Brushless Basics
Post by: andrewh on January 16, 2009, 12:36:27 PM
Sorry about a gap in communication - been busy.

I've taken the time to re-read all the BL posts, and extract from them all the hard data I can about boats and BL motors, and will try and slip it into useful format in the near future .

I find that there are several people to whom I have not (fully ) replied; and I apologise to them - I DID say that I don't have the answers!

Some bits of matching BL motors to boats is progressing in a promising way:
big planing boats (lifeboats and similar) 
"oddball" boats (waterjets and hydrofoils)
some fast electrics

Tugs and other big holes in the water are not supported with much evidence so far,
nor are:
auxiliary yachts

BLB has been inundated by post - well there have been three letters in the postbag :}
I will not deign to dignify Mr. J P Gruntfuttock's letter with a reply, but there are two others which are relevant:

The first is from Disgusted of Worthing:

Well, BLB, I don't think much of Brushless motors after my trials!
I have a 30inch torpedo boat.  I have bought and fitted a Goldenluck 4848/15 BL motor with 80A marine ESC and and 5S3P lipo pack of 10Amp Hr capacity.
Performance is VERY disappointing  - no speed at all, current draw is measured at 0.003 Amps and the water seems to be boiling around the 20mm Nylon prop.
NOT what I expected  from a 800watt motor!

and the second from Incandescent of Bognor:

My tug goes nowhere despite brushless power.  It went well with a 47-pole direct drive DC motor and 110mm 5 blade bronze prop. 
I fitted it with a 2025/2 brushless motor on 12V
The whole drive is VERY noisy, and hot and I don't think much of this bruslesss malarky
Bring back the steam engine, I say
Ian Candescent,
Bognor (regis)

I will reply shortly

Title: Re: Brushless Basics
Post by: oldiron on January 16, 2009, 01:26:50 PM

  I'd like to make a presentation to my model boat club based on your excellent brushless motor thread. May I use any of your posts/diagrams for the presentation?

Title: Re: Brushless Basics
Post by: Bluechrisp on January 16, 2009, 04:36:18 PM
Hello Andrew,

I will look into the higher voltage issues for the SC, it planes with about 2 inches of the bottom showing keel...,  maybe 12V O0
Title: Re: Brushless Basics
Post by: andrewh on January 18, 2009, 10:30:08 AM

Please feel free to make any use of the material you like :}

It would be wise and courteous to contact Martin as well

Title: Re: Brushless Basics
Post by: Martin [Admin] on January 18, 2009, 10:36:57 AM
OK by me too.

Please mention Andrew and Model Boat Mayhem when making your purchases!  ok2
Title: Re: Brushless Basics
Post by: oldiron on January 18, 2009, 11:09:15 AM
OK by me too.

Please mention Andrew and Model Boat Mayhem when making your purchases!  ok2

  Thanks very much  gentlemen.

Title: Re: Brushless Basics
Post by: andrewh on January 21, 2009, 05:10:24 PM

Failure may not be an option to most Mayhemmers, who love their motors like helianthus loves the sun, but failure of Brushless systems are possible and if you know what causes it you will be better equipped to avoid doing that thing!

BL motors - No brushgear, almost universally ballraced, rare earth magnets high electrical efficiency – what can go wrong?
Well, abuse can lead to overheating, and this generally takes a characteristic pattern. 

What is abuse, and how do I avoid it?
Like all electromagnetic devices the worst form of abuse is running them slowly and overloaded!  In Boat terms this means overload due to too big a prop (or other load), or possibly high friction or misalignment in the propshaft, or a bent motor shaft which allows the rotor to catch or rub on the stator.  None of these forms of abuse are very likely in boats – since gravity is kind to them, and loss of control seldom involves tent-peg landings and re-kitting; to which flight motors are (occasionally) subject.

When it comes to overloading unfortunately the efficiency of the BL motor and ESC combination can hide the distress of the motor. 
This is actually far MORE likely among Boat people and especially Mayhemmers (because a lot of advice is passed out to rate ESCs for the STALL CURRENT of the motor.  This means that the ESC often has a current capability WELL beyond what the motor will survive, and the thermal protection of the ESC is useless.

This is probably the subject for another thread, but it can contribute to distress of the motor.  I’m happy to say that our shining experts don’t do this oversizing.

The pattern of failure of a BL motor is:
•   Overloaded motor slows and gets hotter
•   Boat owner compensates by adding throttle
•   Motor gets hotter still, and the coils gradually transfer heat into the rotor
•   Rotor heats up and the magnets lose a little magnetism
•   Boat owner compensates by adding throttle
•   Efficiency drops off
•   and the same throttle opening leads to MUCH more heat (and less power)
•   Eventually
•   The magnets lose a LOT of magnetism
•   Motor efficiency and speed fall
•   One or more stator coils burn out

Failure is always blamed on the burnt out coil but it is generally due to the thermal demagnetisation that led up to it.

Inrunner, outrunner, do they fail the same?
Every word above applies equally to both styles of motor, but there are differences that are worth mentioning.
Remember that inrunners have the rotor completely inside the stator.
he rotor is always VERY small diameter and has the magnets locked into the surface of the rotor.  The windings of the stator are outside this and can be cooled by passing air, or water but in a boat its likely they sit in stagnant, warm air.

Also:  Inrunners can and indeed must run very fast to make any power at all (cos the torque of this little rotor is small) and speeds of 30,000 rpm are not unusual (under load!).
SO they overheat very fast if they are abused!
Inrunners must spin fast
They must sound like a dememted dentists drill to be happy and efficient.

Feigao make BL inrunners from 12mm diameter up to “600 replacement” size – the 12mm size comes in KV up to 7500 rpm/volt, so 10V is 75 THOUSAND RPM unloaded.  Rotor is probably about 6mm diameter.  If you want to make a plastic magic 1/72nd hydrofoil this is a fair place to start

Because they have a smooth and stationary stator they are easy to mount (see next BLB spiel).

For the same reason they can be water-cooled just as easily as a brushed motor – wrap some aluminium or copper pipe round and round them and run cooling water through them

Even if you have a 380 replacement inrunner don’t assume the case diameter is the same as a 380 brushed motor – the manufacturer is only saying that the shaft diameter and fixing holes in the front face are the same as a 380!

There are some inrunners made with built in water cooling – Martin has pictured some in earlier discussions.  Might be worth considering but please see the next statement as well:

But – and this is an andrew-opinion -  Inrunners would be better uncooled and spinning like a screaming dervish, than heavily cooled and slogging!

AndyN has a high-speed Feigao inrunner for his tiny BL speedster.  I think this is a 30 mm diameter motor – often referred to as 380 or 400 replacement.  Andy will be running this with a tiny racing prop and I’m perfectly certain it will spin at astronomical speeds and shift the boat nicely.  Was it 6s or 7S lipos, Andy?


Remember on these the stator is on the inside, and the magnets are fixed to the rotor which whirls through the air  - so the bits which need to be cooled are moving and close to the place they can get the cooling from air.

Air cooling is much easier – many of the heavy-duty outrunners are made with integral fans to keep some air moving over the outside. 
Remember boat-people that if you want air cooling you must provide cooling air!  Think IC engines and allow air into the boat – open a window at the front and allow the hot air out of the back – fit a computer fan if you wish!

Water-cooling, conversely is more difficult.  If you have read Hannu’s posts you will see he has contrived  water-cooled engine mounts for his big BL motors.  This is good  it cools not only the drive –end bearing but also the most massive bit of metal in the motor, and the path through which all the heat has to pass to get to the magnets!  Hyvva, Hannu.

Next chapter - mounting BLs in boats

Title: Re: Brushless Basics
Post by: andrewh on January 21, 2009, 05:20:17 PM
Sorry about the length of the last post - it just grew

I left out the dots in hyvaa - I will pm them to Hannu in Finland

There are a few dangling bits of BL business  - also to be addressed soon.
Title: Re: Brushless Basics
Post by: john54 on January 22, 2009, 05:41:49 PM
 Hi Everyone
I have found this thread extremely interesting and informative :-)
I do have a question I hope someone can answer. I have acquired an outrunner for my boat (hor 25)
the vote has no identification markings at all apart from 2700kv. I have been running her on lipo 3s 30c with a 100amp e.s.c.
In my quest for more speed I would like to try her using lipo4s 15c as I have not got any idea of the specs for the motor other than the kv do you think this would be a wise move? Or should I just try and see. As I am a bit concerned about the rev limit these motors can cope with 39000 off load from 30000.
Any ideas?
Title: Re: Brushless Basics
Post by: andrewh on January 22, 2009, 07:22:05 PM
Hi,  John

We can suggest some things which could help you know what you have and what its doing:

Run a ruler over the motor- outside diameter and length of the parallel bit of the rotor - perferably in mm
Tell us the colour, show us a picture - lots of pictures - the massed ranks of mayhemmers will identify it and probably tell you the assemblers inside leg measurement too:-))

2700Kv tells me that its a hot motor - lots of revs so you should see a few turns of thick wire (on each pole) if you can see the stator windings
Certainly 3S (12V) will not be a problem to any BL outrunner

The key thing is what prop are you running?  You cannot possibly harm the motor by running it on 4S on a small prop, but not knowing much about your setup I can only guess.
2700 corresponds to the KV of a S400, so a 30mm racing prop cannot be too large  - and at 2700Kv 12V will spin it at 32,400 which is going some!  I suspect that you need to go up in prop size to load the motor to something around 20000rpm
What kind of a boat is a Hor25 anyway?

Title: Re: Brushless Basics
Post by: john54 on January 22, 2009, 08:13:10 PM
Motor 3cm x 3cm ,prop 40x, hull hor 25 from Astec 25in x 7.5 mono 1 /2 1.1 kg g.r.p e.s.c 100amp con 120 burst.
Title: Re: Brushless Basics
Post by: john54 on January 22, 2009, 08:16:41 PM
Sorry for c*ap pics (phonecam) :((
Title: Re: Brushless Basics
Post by: tonyH on January 23, 2009, 03:47:30 PM
Hello All,

If I assume that an ESC per motor is the safest way to go with brushless and I don't need reverse (The boat is twin water-jet driven), are the individual motor revs synchronised in any way by the signal from the Rx through a 'Y' lead? If not, is there any easy way to do this? The motors are 600Kv outrunners and I'll probably run on 19.2V.

Any ideas would be appreciated.


Title: Re: Brushless Basics
Post by: andrewh on January 29, 2009, 09:19:24 PM

There is a previous discussion (andrew rant) in this thread about using multiple motors off a single brushless esc.

 Summary: it has worked for many but not all people.  If you are happy to stay "forward only" small aero ESCs are very cheap and its probably not worth trying unless you are a keen experimenter.

Yes - you plug them both into the throttle channel with a y-lead

I will here mention that an Amp to a model flyer is an AMP, and a 10A aero ESC will pass 10 Amps 24/7 with bursts to 15 but to be fair they like fresh air!

Normally water-jets are line duscts fans and like revs in unlimited quantities .   600Kv and 19.2 V gives revs of  11,500 which I do not believe is enough - I would expect to START at twice that and go up from there, but I must confess I do not have a water jet - -could you please tell us which jets you are using?

I think that Hannnu, and certainly a british gent I met at Warwick (water-jet lifeboat) have relevant experience of driving waterjets.
Tony - do you have these motors yet?

Title: Re: Brushless Basics
Post by: tonyH on January 30, 2009, 11:42:05 AM

Thanks for the input.

The jet drives are home constructed using the actual KaMeWa 375S as the model. Dimensionally they are similar to the Kehrer 40mm units which call for a rev range of 10-15000 rpm. I'm not after ultimate speed, just a fair scale speed, so I can up the voltage if necessary and play with the pitch of the 'props'. Also, as you mention, forward only is required, so I'll probably go for a 30amp unit to start.

The motors are the Thumper 4250's I'd seen reviewed in one of the electroflight mags and, coincidentally, had been used by Andy on another thread.

Of course, the drive units could just blow up but since the total material cost for the 2 was less that a fiver, compared to the Kehrer units at 130 quid each, I'm not over concerned. It'll be fun trying.


PS The actual KaMeWa units run at 3000 rpm or so.

Title: Re: Brushless Basics
Post by: andrewh on February 04, 2009, 12:38:54 PM
Tony, thanks for the picture - very nice copperwork

Sorry to be less than optimistic, but if the Kehrer units are intended for 10-15K rpm, your Thumpers would need at least the 19.2 V you mention to even get out of bed.

I don't have experience (yet) of water-jets (but have been inspired by Umi) but I understand that they do very little below some critical RPM, then pull like gangbusters :}  This is exactly what a Ducted Fan does in the air. 
Thrust is zilch until the dogs start howling then it rises fast as the revs increase.

I don't know if you have planned or made the impellers yet, but if not it might be an idea to incorporate as much pitch as you dare to make use of the revs available. 

Are you going to dive straight in with the twin, or might you lash up a one-jet trial boat as a system proving device?


Title: Re: Brushless Basics
Post by: tonyH on February 04, 2009, 02:49:36 PM
Hi Andrew,

I agree about 'the hump' but there are a couple of things that have pointed me to the 600Kv/20volt system (Although I could run up to 26 volts) and they are as follow.

1. Both the other threads on jet drives tend to the same direction. Alan (debssnal) uses the same motors and has run on both 12 and 24V on his 15Kg boat (mine is 12kg max) and Hannu runs his 500Kv motors, if I read it correctly, at 13,000 rpm which equates to 26v.
2. The maximum revs for the real KaMeWa is low and I think that this may relate to the incompressability of water, compared to air in a ducted fan. The area difference between the inlet side and the outlet side of water jets seems to be about 3:1 which also appears higher than any ducted fan I've seen but I'm certainly no expert.

The impellers are oversize Graupner carbon props to give maximum blade area, reshaped at the ends to follow the tube size with minimal clearance, so are easy to replace or change. Both jets are made but each has a different pitch prop for testing.

It really is a case of trial and error, however, brought about by not being wiling to spend loadsamoney on the jet units! I've a spare 1m offshore racing hull which I can use for trials. whatever the result, I'll post the matter on here - red face 'n all!

Title: Re: Brushless Basics
Post by: andrewh on February 04, 2009, 07:02:01 PM
FBO  (flash of the blindingly obvious)

“Yet never had I breathed its pure serene
Till I heard Mayhem speak out loud and bold”
Then felt I like some watcher of the skies
when a new planet swims within his ken”

I have been much considering some way of getting a little measurement into the vexed question of applying BLs into boats of all sorts.

I have been thinking  - and may well have said – “why isn’t there a list/table/chart of boat propellor diameters, pitches powers revs and what they are for?? like there is for airscrews”

The question, of course, also contains the answer but I didn’t see it till a week or so ago and I have been as busy as a one-legged tap dancer this week with the day job.

Why don’t boat props have the same level of science? 
Because they don’t need it!  Boats don’t fall out of the water if they fail to produce the necessary thrust or speed


Lets use the published tables (for airscrews) as they affect the motors.  They are enormously detailed, with power figures and REVS at the whole range of voltages they might be used at (We boaties will probably use less volts because there is no need to stay above stall speed).

For every motor we are likely to use , at every voltage we know the RPM and power (and current, and voltage) for a whole range of props from little to huge (for that motor), and there are generally warnings like “do not run at this power level for more than 1 minute  “speed toooooo high – bearings may frag”  (I made the last one up).

When time permits I will take a published set of data about a motor that we might be playing with and see how we might use it to calculate speed, revs, amps power, “WOW” factor

Title: Re: Brushless Basics
Post by: tonyH on February 04, 2009, 10:39:44 PM
Is this Martin's Homer?

Title: Re: Brushless Basics
Post by: andrewh on February 05, 2009, 09:51:07 AM
Tony - that's the one!

I have not quoted the last two lines because of my desire not to offend the Pekinese owners :D (or indeed citizens with gravitational enhancement)
Title: Re: Brushless Basics
Post by: tonyH on February 07, 2009, 06:59:43 PM
Sorry, you've lost me on the 'Pekinese' front?

Title: Re: Brushless Basics
Post by: andrewh on February 09, 2009, 12:40:20 PM
Apologies to Tony and other puzzled readers - I have been obscure :((

The last lines of the sonnet "On first looking into Martin's homer" are:

"or like stout Cortez when with eagle eyes
He gazed at the Pacific; and all his men
looked at each other with a wild surmise,
silent; upon a peke in Darien."

So thats the reference to implied cruelty to lapdogs, and alleged obesity. 
Sorry to have been abstruse - I've never done it before. :} honest
Title: Re: Brushless Basics
Post by: dreadnought72 on February 09, 2009, 01:33:01 PM
Not obscure at all!

We're just so smart on here that we know it was really skinny Balboa who first gazed at the Pacific from Darien, not stout Cortez, so we didn't think of considering Keats who'd-got-it-wrong. That's the same Keats who - unless our Mayhem-leader has been translating Homer on the sly - was "pekenesing" into Chapman's Homer when he incorrectly stuck pen to paper.

Andy, 30 years after being made to read that stuff, now wondering whether woodwork would have been more useful.
Title: Re: Brushless Basics
Post by: tonyH on February 09, 2009, 02:48:39 PM
Obviously a Grauniad reader!

There I was, ploughing through The Feast of the Poets etc.etc. for inspiration and all the time it was a typo!

Nice one Andrew!
Title: Re: Brushless Basics
Post by: andrewh on February 09, 2009, 05:08:18 PM
Sorry chaps - I had a "good" education in Scotland before Pontius got his wings so poetry and literature waxed large and I know, but don't speak, dodo (latin)

Yes woodworking much more useful - we had hundreds of hydulignum blades off markll Hurricanes for cutting up as wood-turning blanks
Might get back to Brushless before long!

Title: Re: Brushless Basics
Post by: tonyH on February 09, 2009, 06:05:19 PM
I always thought that we built a wall to prevent the Scots from learning Latin? 
Title: Re: Brushless Basics
Post by: andrewh on February 09, 2009, 08:51:36 PM
Crivvens, the sheer ignorance of these sassenachs :}

Having said that I'm one too, but brought up by the highland line.
The Romans lived and traded far north in Scotland for centuries, built the Antonine wall from the Forth to the Clyde as well as Hadrian's wall.  I've always assumed that Hadrian's wall was the last and largest but I confess I don't know the timeline well.

Onyhow, it failed!
Title: Re: Brushless Basics
Post by: andrewh on February 24, 2009, 12:47:20 PM
Rejoice with me :}
Not only has my body survived to reach its 60th birthday (mind somewhere between 4 and 6 years old, according to my womenfolk)

But also I have located the problem with my brushless CDROM motor :} :-))

The its-gone-silent-without-smoke mini-tutorial
This little feller went totally silent in the middle of trial runs in Razor the BL trial boat, and I had not applied enough diagnostic science until today.
Fortunately at work we have low resistance meters by the yard (cos we make low resistances) so I was able to accurately check the resistance of all the windings (0.205 Ohms between any two leads - so EACH winding is half that)
So the problem is not electrical :}

Pull off the rotor (on little BL motors there is no mechanical fixing - even with an airscrew) and reverse the shaft - rotor turns like silk - its not the shaft or bearings in the stator :}

Apply engineers blue (actually black felt-tip) and rotate motor
Note - ALL BL motors feel very "coggy" as the powerful magnets snatch at the poles
Ssms scratchy as well as coggy, and there is blue left on two of the magnets
Eureka - diagnosis and solution :} :-)) :}
Note magnet sticking to blade of knife?
Magnets were attached to the bell with cyano - and the cyano has relaxed as a result of water, heat or both.  It appears that the magnet has got "foam" Cyano behind it - perhaps it overheated the glue while hardening?

Fairly difficult to easily diagnose - the magnet was barely loose - it just flexed inwards a little  - I don't know if it physically touched the stator - but it certainly got so close it magnetically "stopped" it
Solution - remove all the magnets (soak in acetone or cellulose thinners) replace (perhaps using epoxy and microbaloons)
Install motor in White Dwarf (thank you very much, generous donor)
Try it  and tell you

Is this a failure that you -  the great BL-using public - should worry about?
No, its Andrew's trial motor (and the first he ever built) which stopped for a predictable reason.
Commercial BL motors would not have this issue, and nor would my later ones

Title: Re: Brushless Basics
Post by: dreadnought72 on February 24, 2009, 01:24:02 PM
Many happy returns!

(And revolutions, where the motor's concerned.)

I reached forty-six a few days ago. And so I'm switching to Martian years.

Andy, 24.5
Title: Re: Brushless Basics
Post by: andrewh on February 24, 2009, 01:44:45 PM
Andy 24,5
Many happy returns, too
You don't look a day over 30 :},
and you are my planking hero!

Is the 24.5 in Martian years? or is it the hat size?
Any progress on the OCB?

andrew, 1 of the 10 types of  binary mathematicians

Title: Re: Brushless Basics
Post by: col426 on February 25, 2009, 05:45:39 AM
Hello all.
I've been reading this thread with interest, trying to learn more about brushless motors.

I've got a Cen Waveshark, like a jetski, which is 720mm long by 260mm wide into which I've put a KMB 33mm jet drive (one of these:,shop.product_details/flypage,shop.flypage/product_id,18/category_id,5/manufacturer_id,0/option,com_virtuemart/Itemid,17/ (,shop.product_details/flypage,shop.flypage/product_id,18/category_id,5/manufacturer_id,0/option,com_virtuemart/Itemid,17/)).  It's currently running a .18 nitro engine producing about 1.184 horsepower and about 20,000 rpm.  The standard electric motor KMB run on this jet-drive produces about 19,200 rpm.

I'd like to put a brushless setup into it, as it's too much muck-around, and too messy with the nitro engine.  I'd also like to get more performance!  I've read on this thread that revs is what I need, and a brushless inrunner with a high KV rating. I've been looking at this KB45 brushless motor (, with a brushless controller like this: (  I'm looking at running it on 14.4 volts as I already have dual 7.2v Nickel-Metal-Hydride battery packs which I run in my E-MAXX monster truck.

My question is will this do the job?  Also, what is the difference between S, L, & XL motors?  Obviously they are short, long, & extra long, but it looks like the longer they get, the KV rating drops for the same number of winds.  Does anybody know what this is about, and where you would use the different motors?

Thanks for your help, any assistance would be gratefully received!

Title: Re: Brushless Basics
Post by: andrewh on February 26, 2009, 01:25:23 PM
Hi, Phillip

I see you are in tasmania  - glad you are on board :}

Why, oh why do most of my replies start off - I don't know the answer/whole answer/question?
Sorry, but here is another "don't know the whole answer", but your question has lots of the right information built in - so lets see what research and arithmetic tell us.
Thanks for the links - they are just what is needed

First the KMB 33mm waterjet - the webpage says the power requirement is about 650watts at 15000 to 20000rpm - so it is not a crazy-revs device.  There are several motors quoted as suitable - and I tried to identify these in motocalc
and managed to reasonably identify the Pletts - these are about 800 to 900KV, and the reccommended Johnston 800 is 1200KV

Please don't be guided by the advertised power of your IC engine - go by KMB instead! :}
a few more revs will probably not harm the mechanics - Germans build solid kit!

The Brusless you have selected is an inrunner, and the highest of the KV versions of its family.  Its a huge motor - well over a pound weight and the power is written as over 3KW!  (although the discussion suggests that this, too is mythical and would be accompanied by splashing copper)
at 14V this motor would be turning at 32,000 Rpm.  Impressive, but possibly more than the water-jet bearings would like :((

I suggest looking at one of the more modest KV versions of this motor - around the 1500KV level which would give you the revs at 14V
In answer to your other question - the different versions are made for basically the car and aircraft users - we flyers want to direct drive huge efficient props, but sometimes the ground prevents big diameters so we need to swing a smaller prop faster, or work through a gearbox so there is always a need for several different KV motors in every size.

Plane digression - the same motor frame might have to fly a scale DVll with a 30x10 inch prop on direct drive (2200 RPM), a scale reno racing mustang with a 7x7 prop (17500 rpm), a ducted fan at 37,500 rpm,   or a heli with 30:1 main gear.  Add to that the different voltages to be used and viola! you have a big range of KVs in every motor type

  Since this is an inrunner  - it is not likely that the core length varies (but a close study of the weights would tell you that) - it is more likely that there are several different winds
 from the 2300 you mentioned - 2 turns of fence-wire
to the 650KV version    500 turns of maidenhair wire
(In fact the winds are mentioned somewhere in the literature)
OK, so I exaggerate :}

ESC can be any that will take the current - and follow the revs intended.  You will have no need of reverse from the ESC, as this is done with buckets on a water-jet.  (There is, BTW a purpose made ESC for water-jets which incorporates the servo movement for bucket reversing in the throttle stick movement)
The one you referred to looks the business, and none should have any trouble at 20 to 25 K revs/min

Best of luck - please keep us posted on progress - with pics!


Title: Re: Brushless Basics
Post by: boatmadman on February 26, 2009, 01:35:45 PM
Great stuff, by coincidence I have recently aquired one of these:,com_virtuemart/page,shop.browse/category_id,11/Itemid,17/

and am now wondering what to power it with, and what to put it in - did think of a springer, but it might be a touch too fast  ok2

The esc you mention that incorporates reverse bucket control, who make them?
Title: Re: Brushless Basics
Post by: andrewh on February 26, 2009, 01:44:48 PM

How about one of the stealth warships - Visby or similar?

The Combo ESC was by (or at least from)  one of the german manufacturers  - Graupner or Robbe for one of their WJ boat kits - Martin has written about it in another thread.  I will try and find it, but my Home internet is having hiccups.

I am going to lie down in a darkened room - the thought of a 1.5 KW water-jet springer has fried my brian.
Title: Re: Brushless Basics
Post by: boatmadman on February 26, 2009, 01:55:45 PM
Stealth warship looks promising, anyone know where plans are available?

Andy, sorry to hear your Brian is fried  :}
Title: Re: Brushless Basics
Post by: andrewh on February 26, 2009, 02:19:38 PM

there is a good thread on
which might inspire you. 
I know that the gent made his own plans (origami :})

Googling Visby might find you some plans
don't worry about my brian - its beyond both spelling and help
Title: Re: Brushless Basics
Post by: andrewh on February 27, 2009, 01:17:04 PM
News of the Andrew brushless stable:

The little sick motor diagnosed a few posts ago has been repaired and works well again, but a little stuttery and uneven.  Because I have and optical tacho I will attempt to measure the revs - and hence KV.

Homemade BL CDROM motor from a GoBrushless kit  - I was inspired and finished her off - runs smoothly and apparently powerfully.  The speed control is notably very good - I will also measure the speed and KV of this one

Might commit speedboating with White Dwarf this weekend and relay it to you with new camera
Title: Re: Brushless Basics
Post by: DLM on February 27, 2009, 04:27:35 PM
I've been reading the winding of Andrewh posting and wouldn't it be cheaper to buy the guts with different windings for different situations like bigger boats or pleasure boats or racers. Now i don't mind working at all but is it possible to buy the guts and do the wiring yourself. I'm  a brushed motor guy but am on a learning curve of bl so excuse my lack of bl terms. I'll continue reading on page #2. Thanks.
Title: Re: Brushless Basics
Post by: boatmadman on February 28, 2009, 02:10:38 PM
Would the water jet I mentioned above be capable of pushing a 1m to 1.5m planing hull like Visby?

I have started designing something myself :-))

Title: Re: Brushless Basics
Post by: col426 on March 02, 2009, 04:09:46 AM
Hello Andrew.
I trust your Brian has recovered...!  %%

Many thanks for your thoughts and insights on these motors.  Obviously I'm a member of the more is better club...I hate being so predictable!  :}

I'll have a think about your advice, and might drop back and try the KB45-10L 1800kv, perhaps with a step down to the KB45-12L 1400kv if that is too much.  I'll only be running them at 14.4v, less than half their rated voltage, so hopefully their output should be a bit calmer.  They just seem to offer so much performance (on paper anyway) for so little price (comparatively speaking).  If I wanted to buy a Hacker, etc with similar performance, I'm sure I'd be paying the proverbial arm & leg + my firstborn.  Also, most of the other cheaper brushless motors seem to be a lot lower powered, or just don't list their power rating.  The purpose-made water-jet ESC sounds interesting too, I might have to investigate that further.

I've included a couple of pictures of how the jet ski is currently, with the nitro motor & water-jet drive (it used to have normal prop drive before I got at it :}).  When I get around to converting it, I'll post more pictures.

Title: Re: Brushless Basics
Post by: andrewh on March 03, 2009, 02:42:30 AM

You have hit one nail on the head - it is perfectly possible to buy a BL motor or even a kit - and rewind it to suit what you need. 
HOWEVER - it is just as easy to do exactly that with a brushed motor - and how many people do you know who salvage a 2.4 Volt motor from a 2-cell screwdriver and rewind it for 12V working with a 10 inch 4 blader tug prop?

And BL motors are cheap now, and will get much cheaper (IMHO) if the pound strengthens a bit.

I am absolutely certain about this.
With enough power, yes.  Visby moves about smartly (the full size, that is) but not indecently fast.  Have a look at Hannu's posts about a big jet boat - I seem to remember powers in the KW range - but you don't want his radical performance.
What do you mean, you do?   Well, yes, so would I; but I remember Hailwoods law, which says " the throttle goes both ways"   :} the power, but use as much as seems good at any time

I once heard Jock Russell, a racing driver who fitted a full race Ford V8 into a 1.5 litre Lotus F1 chassis, say "if you are going to be a bear, be a grizzly"  How true!
Thanks for the pix - I like the short tuned pipe.  I can agree with the revs you were talking about.

I think the 1800KV version might be a good bet - you will get lotsa revs at 14V, and if you feel the need for speed, go for more volts! :}
If you can run to it a water-cooled ESC might be a good bet - or make a cooling bed for an a/c one.  I would go for a cheap aircraft 60A unit and try and give it a cool life - poke it out into the air, or give it a battery fan of its own.
You might be able to emulate the W/J control with one of Action Electronics devices which (I believe) can mix any controls in any way - so it should be possible to do ESC from say 20% to 100 % throttle and reverse bucket servo from 20% to 0
FLJ will advise if asked, and the website is excellent

Lots of the Motor supppliers give all the performance data for alll their motors - I have mentioned the Micron R'C site before - it is excellent, and so are they as suppliers.  The area on scorpion motors has data on the whole range - and also a calculator AND a table of equivalents of the various manufacturer's products


Title: Re: Brushless Basics
Post by: andrewh on March 19, 2009, 01:15:00 PM

Sorry - been a lot going on in the last month, family-wise and I'm off to the Americas for a week so I thought it would be a good idea to throw in an update and stir the BL cooking pot before leaving on the big white bird.

Micro-inrunner kit!
While looking round the Car section of a Leicester model shop (Phil's models?) I found a kit of tiny inrunner brushless with reversing ESC for a BL replacement for tiny RC cars.  Motor is a 12m diameter (same as the feigao 12mm ones) but in a very short length - about 20mm
Not cheap, but it would make a tiny boat SCREAM.  I didn't notice the KV, but would guess at 7500 or so!
I see that the cars are 1/36 or thereabouts, use 130 motors as stock and Mini-Z is  one of the types

BL Trial Boat

Heading for the water again - I have glass/epoxied the shaft hole, just to get a good base to start from, and figured out the BL motor mount system, so about an evenings work to get ready for the water :}

BL TUG (shameless plug)
(and it rhymes)
Did you all see Alans post -
That is one impressive water-shifting tug, and Alan has told us all the details, motors, props etc
My impression (and it is only an impression) is that the motors are running cool, gentle and efficient with these props and Alan's well-controlled thumb.  Again the gel cell (s) are not smoking, so the current is not excessive, and duration is good
So, thanks Alan, thats one of the key corners of boat operation demonstrated :-))

while in canada I am meeting some footy* heroes!  Excited, or what :}
* thats 12 inch racing yachts
Title: Re: Brushless Basics
Post by: tobyker on May 01, 2009, 08:38:35 PM
Andrew this is ever so interesting. I'm thinking of getting a Graupner minijet for a 500mm styrene hull, and putting in one of the Vortex inrunners as supplied by Tony Hill  (  as these seem reasonably priced and seem to have the revs on 10v. would I need the 480 equivalent or do you reckon I'd get away with a 400?

I've got a wee bell motor driving a 18" loa by 9" beam airboat which goes like a rocket!

I must wrap a wet towel round my head and read your primer again slowly. SWMBO thinks I'm looking at naughty things as I've spent so much time on the PC reading this thread in the past few days!

Many thanks
Title: Re: Brushless Basics
Post by: bbdave on July 13, 2010, 10:31:50 PM
I'm looking at a motor the number on it is 1717 which deffinately is not the size so what do they mean? what are the differences between say an emax motor and a castle creations apart from the price?
Also if i want a 1500kv motor there is a huge difference in physical size i presume a small motor wont have the same power as the larger which has more torque simply because of the size difference is that correct?

Title: Re: Brushless Basics
Post by: nick_75au on July 15, 2010, 09:36:39 AM
Most likely it is the size, of the stator(bit with windings on it) if its an outrunner. Kv has very little to do with motor size, Power handling is the difference between different sizes of the same Kv motor.
Title: Re: Brushless Basics
Post by: roger on July 17, 2010, 11:48:50 PM
Thank you Andrew. Not only especially informative but very entertaining too. If only I'd looking in the last place first!

You did say there are no dumb questions, so my "not dumb" question is: if all brushless motors need an ESC why aren't they built in to the motors?
Title: Re: Brushless Basics
Post by: roger on July 18, 2010, 09:12:06 PM
Hi Andrew,

Maybe you’ve moved on to other things by now, but, if you are still here, perhaps you would consider non-silly question number 2.

It’s a long time ago back to December 2008. (Actually it’s just two days ago for me since I just got here).  I follow the ABC to ACB (or swap any two for that matter) to reverse your BL.  What I don’t understand is your “Mk 1 Pencil” note “DON’T PRESS PLUNGER WHEN THE MOTOR IS RUNNING”. What happens (fried Brians aside) if I do?
Title: Re: Brushless Basics
Post by: nick_75au on July 19, 2010, 05:24:29 AM
Hi roger,
Maybe I can answer both questions
1, Some brush less motors do have them built in, I.E computer fans but they are not very versatile as they are fixed speed, just like a brushed motor straight off a power supply.
 The same reason brushed motors don't have one built in, different applications have requirements that vary, such as reverse, soft start, braking and RPM hold(governor) Its immpossible to make a "do everything" ESC without it being expensive and complicated.

2' the same reason you don't put your car in reverse when still moving forward, the other reason is the ESC is sensing voltage from the non active phase If that suddenly has voltage on it it may damage the esc.

Title: Re: Brushless Basics
Post by: roger on July 19, 2010, 06:24:05 PM
Thanks for your prompt response Nick. That all seems quite logical.

However, I'm not sure your car analogy really fits here. While my car has brakes, the "brake" on a boat is throwing it into reverse. I certainly wouldn't want to blow up my esc. (In fact I'm still gathering the kit together as I haven't used brushless motors before, so I don't actually have the bits yet for even a controlled bench-test.)

Since the brain (such as it is!) is more readily available than the cash at the moment, I guess I need to drag out my thinking cap from the bottom of the scraps box and dust it off.

Electronically I suppose I'd monitor the signals in the three power leads and select the appropriate moment (presumably when there are no signals) to do the AB - BA swap. I guess this is something like the way reversing ESC's work anyway, so I needn't try to re-invent the wheel.

[Going off at a tangent, did you read about the guy who built a £4.50 (about A$8) toaster from scratch - ie metal ores, crude oil etc. It took him six months, cost £2000 (labour not included) and blew up after thirty seconds operation!]

Mechanically, I guess I could rig up an interlock that allows Andrew's reversing microswitch(es) to throw only when the propshaft is stationary. Of course it would have to work both ways - ie from backwards to forwards as well. Maybe it would be better to stick with a one-way only motor and hang a couple of reversing buckets off the Kort rudder.

For my next tug (even though I've barely started this one) I fancy fitting an asimuth drive. Adam's setup in Reply #10 of Brushless Motors in Tugs - ( - looks really neat.
Title: Re: Brushless Basics
Post by: malcolmfrary on July 31, 2010, 09:39:24 AM
The logical way to avoid cooking the motor/ESC when reversing is to have a "soft" response to the stick.  That way, the mechanical bits have a chance to keep pace with whatever the electronics are doing.
Title: Re: Brushless Basics
Post by: sailorboy61 on July 02, 2012, 02:43:45 PM
Following the links reading through the posts, I noticed this:
Title: Re: Brushless Basics
Post by: Martin [Admin] on January 21, 2013, 07:53:52 PM
 On Youtube - RC BASICS: What is KV? (
Title: Re: Brushless Basics
Post by: wayne quigley on May 01, 2013, 09:38:26 PM
8sorry am I missing some thing
inrunners  have a fixed can and the internals spin just like a brushed motor.
outrunner have the intenals fixed and the can spins???the problem is i have been searching for motor for a 46" fairy huntsman and all the outrunners i have seen seem to have a fixing bracket fixed to the can and the cable attached to the can.
where am i going wrong
Title: Re: Brushless Basics
Post by: malcolmfrary on May 02, 2013, 10:22:32 AM
Picture of outrunner - (
Wires to static winding on backplate which also carries the spindle bearing, the drive shaft comes out via the backplate/mounting.
Title: Re: Brushless Basics
Post by: nick_75au on May 02, 2013, 10:30:35 AM
One end of the "can" is fixed, this is your mounting point the same as a brushed motor and where the wires come out, the rotating can is more like a rotating cup and the "lid" stays still.

In both cases its the magnets that rotate while the windings stay still.

Title: Re: Brushless Basics
Post by: wayne quigley on May 02, 2013, 08:23:51 PM
thanks i have beeen on YouTube and seen how they run now all clear when you see them in action.
also is there any way of not having to input Verification questions for each post,a right pain in the rear
Title: Re: Brushless Basics
Post by: Tug Fanatic on May 14, 2013, 01:39:09 PM
Brushless motors come in a variety of diameters & lengths. With brushed motors there was generally much less choice but can diameter was a good indicator of prop size compatability.
With a pair of brushless outrunner motors if one is short & wide but the other is long & thin & they both have the same kv & maximum current rating would you know which was the better motor for particular applications? Do the same rules apply?
Title: Re: Brushless Basics
Post by: Martin [Admin] on August 31, 2015, 08:05:13 AM
RC BASICS: What is KV? : (
Title: Re: Brushless Basics
Post by: Martin [Admin] on August 31, 2015, 08:31:00 AM

Another video:
Title: Re: Brushless Basics
Post by: tugboatg on September 01, 2015, 04:11:46 AM
Any help with Brushless outrunner motor to fit MFA 2 to 1 belt drive ?  39 inch twin screw tug
Title: Re: Brushless Basics
Post by: andrewh on February 23, 2016, 04:34:00 AM
Hi, tugboatg

The MFA drive is made to fit any and all motors of size 540, 550, 600 and many more with similar numbers, and has been made to fit a S700 with a little machining

So the basic answer is any brushless with 540 front-end fixings, or could be modified to it.  I suspect the small gear is bored for the 540/600 shaft ,which is 1/8" but no doubt you could bore it a little bigger

The simplest answer is probably the worst - many of the car inrunner brushlesses are made to fit the 540 mount - but they are the very wrong motor for a tugboat, as they are generally high-speed, low torque.

Remember that in the brushless description the first figure is the rotor diameter (EG a 3560 1050kv motor is 35mm diameter) 
Since a  540 is 35.8mm diameter with 2 fixing holes at 1" centres any outrunner with a diameter 35 mm or less should fit onto the face of the belt drive

For a tug, I feel that you probably want max Torque and low revs, so this equates to a low Kv
(altho' of course the belt drive is more than halving the prop revs (my memory says its a 2.3:1 ratio)

hope some of this helps
Title: Re: Brushless Basics
Post by: Onetenor on October 30, 2018, 05:32:53 AM
Seen this?===
Title: Re: Brushless Basics
Post by: malcolmfrary on October 30, 2018, 09:13:56 AM
Manages to say a great deal without actually telling anything useful.  What numbers I understood indicate a fairly anaemic control that needs something like an Arduino to control it, rather than being something that plugs into a radio.
Title: Re: Brushless Basics
Post by: andrewh on October 31, 2018, 05:05:45 AM
Thanks, John and Malcolm
Its a Maxon evaluation unit and, as the article says, is aimed at control.  It mentions pick-and-place as the type of thing that it might be used for. 
Maxon are experts in precision tiny motors - one of the first sources of coreless motors in the 1980s, and not cheap

Interestingly; the photo is not very related to the article  - the illustration is many times larger than the mentioned size of 20.38mm x 24.2mm