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Author Topic: Brushless Basics  (Read 72454 times)

andrewh

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Brushless Basics
« 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 http://www.rcgroups.com/electric-motor-design-and-construction-361/
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

andrew

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Martin [Admin]

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Re: Brushless Basics
« Reply #1 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.   :-))
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andrewh

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Re: Brushless Basics
« Reply #2 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
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:
http://images.google.co.uk/imgres?imgurl=http://adamone.rchomepage.com/brushless.gif&imgrefurl=http://adamone.rchomepage.com/guide5.htm&h=144&w=180&sz=36&hl=en&start=60&usg=__5GK2EQiOE-vJexKA6q1zYQ0vViE=&tbnid=7d-_kO5hHhSjOM:&tbnh=81&tbnw=101&prev=/images%3Fq%3Dinrunner%2B%252Bbrushless%26start%3D54%26gbv%3D2%26ndsp%3D18%26hl%3Den%26sa%3DN

I see that this animation runs - there is a lot of good general motor information on the site
http://adamone.rchomepage.com/guide5.htm

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.
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!
andrew

as always  - comments and contributions welcomed

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andrewh

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Re: Brushless Basics
« Reply #3 on: November 03, 2008, 02:38:09 PM »

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kiwimodeller

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Re: Brushless Basics
« Reply #4 on: November 03, 2008, 10:50:15 PM »

Even this dummy can understand so far, keep it coming, thanks, Ian.
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andrewh

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Re: Brushless Basics
« Reply #5 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

THE RANGE OF POWER, REVS, TORQUE AND SIZE IS SO WIDE THAT ALL BOATING NEEDS CAN BE MET USING DIRECT DRIVE.

Preamble:
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.
Andrewguess:  
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)

Conclusions
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?
andrew

 
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roycv

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Re: Brushless Basics
« Reply #6 on: November 06, 2008, 02:50:10 PM »

Can I also say keep it coming most instructive and easy to understand.
regards Roy
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andrewh

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Re: Brushless Basics
« Reply #7 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 :}
andrew
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JayDee

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Re: Brushless Basics
« Reply #8 on: November 06, 2008, 03:48:17 PM »


Andrew,

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

John.  :-))  :-))  :-))
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andrewh

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Re: Brushless Basics
« Reply #9 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!
andrew
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Seaspray

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Re: Brushless Basics
« Reply #10 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   


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roycv

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Re: Brushless Basics
« Reply #11 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
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andrewh

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Re: Brushless Basics
« Reply #12 on: November 10, 2008, 11:48:05 AM »

Roy

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 :}
andrew
Don't mind me - I had a great weekend
warwick/PT boat quiet and fast/sailed my submarine yacht :D
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kiwimodeller

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Re: Brushless Basics
« Reply #13 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.
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andrewh

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Re: Brushless Basics
« Reply #14 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)
http://www.modelboatmayhem.co.uk/forum/index.php?topic=9830.0

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:


Specification    
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 :}
andrew
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Garabaldy

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Re: Brushless Basics
« Reply #15 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 :-))
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andrewh

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Re: Brushless Basics
« Reply #16 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)
andrew
bedecked in sackcloth
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roycv

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Re: Brushless Basics
« Reply #17 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
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roycv

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Re: Brushless Basics
« Reply #18 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.

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andrewh

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Re: Brushless Basics
« Reply #19 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:
Do-how
Before my Hellkitten
  http://www.modelboatmayhem.co.uk/forum/index.php?topic=8783.0
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:
  • Small propellors
    Low ratio gearing – something like 2:1 or 3:1
    Low voltages – I do not know whether brushless ESCs will operate to supply the motor s with., say 3V.  If they will , this would be a great solution.  (PLEASE don’t point out that the ESCs say 6 to 24V or whatever – this is a different question)  I will give it a try this weekend.
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:
  • Big wire
    High currents
    Low volts
    High KV (revs) per volt

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

andrew

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roycv

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Re: Brushless Basics
« Reply #20 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
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Martin [Admin]

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Re: Brushless Basics
« Reply #21 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? )

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andrewh

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Re: Brushless Basics
« Reply #22 on: November 17, 2008, 04:29:18 PM »

Martin,

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
http://www.teamnovak.com/products/brushless/motor_spec_chart.htm
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

andrew
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 :}
BB)
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Re: Brushless Basics
« Reply #23 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.  :-))
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andrewh

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Re: Brushless Basics
« Reply #24 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"

andrew





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