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Author Topic: Brushless Basics  (Read 73071 times)

andrewh

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Re: Brushless Basics
« Reply #50 on: January 12, 2009, 09:52:33 AM »

Ernie,
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?

tia
andrew

[edited - speling]

 
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andrewh

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Re: Brushless Basics
« Reply #51 on: January 12, 2009, 10:27:53 AM »

Chris

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

andrew
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andrewh

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Re: Brushless Basics
« Reply #52 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:
warships
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!
Disgusted,


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
andrew
 




 
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oldiron

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Re: Brushless Basics
« Reply #53 on: January 16, 2009, 01:26:50 PM »

Andrew:

  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?

Thanks
John
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Bluechrisp

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Re: Brushless Basics
« Reply #54 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
ChrisP
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andrewh

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Re: Brushless Basics
« Reply #55 on: January 18, 2009, 10:30:08 AM »

John

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

It would be wise and courteous to contact Martin as well

rgds,
andrew
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Martin [Admin]

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Re: Brushless Basics
« Reply #56 on: January 18, 2009, 10:36:57 AM »

OK by me too.
 Martin

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

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Re: Brushless Basics
« Reply #57 on: January 18, 2009, 11:09:15 AM »

OK by me too.
 Martin

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


  Thanks very much  gentlemen.

John
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andrewh

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Re: Brushless Basics
« Reply #58 on: January 21, 2009, 05:10:24 PM »

Failure

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.
Inrunners
Remember that inrunners have the rotor completely inside the stator.
T
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?

Outrunners

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.

andrew
Next chapter - mounting BLs in boats

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andrewh

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Re: Brushless Basics
« Reply #59 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.
andrew
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john54

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Re: Brushless Basics
« Reply #60 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?
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andrewh

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Re: Brushless Basics
« Reply #61 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?
andrew




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john54

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Re: Brushless Basics
« Reply #62 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.
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john54

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Re: Brushless Basics
« Reply #63 on: January 22, 2009, 08:16:41 PM »

Sorry for c*ap pics (phonecam) :((
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tonyH

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Re: Brushless Basics
« Reply #64 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.

Thanks

Tony
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andrewh

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Re: Brushless Basics
« Reply #65 on: January 29, 2009, 09:19:24 PM »

Tony,

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?

andrew
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tonyH

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Re: Brushless Basics
« Reply #66 on: January 30, 2009, 11:42:05 AM »

Andrew,

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.

Tony

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

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andrewh

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Re: Brushless Basics
« Reply #67 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?

andrew

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tonyH

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Re: Brushless Basics
« Reply #68 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!

Tony
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andrewh

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Re: Brushless Basics
« Reply #69 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

SO

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

andrew
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tonyH

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Re: Brushless Basics
« Reply #70 on: February 04, 2009, 10:39:44 PM »

Is this Martin's Homer?

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andrewh

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Re: Brushless Basics
« Reply #71 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)
andrew
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tonyH

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Re: Brushless Basics
« Reply #72 on: February 07, 2009, 06:59:43 PM »

Sorry, you've lost me on the 'Pekinese' front?

Tony
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andrewh

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Re: Brushless Basics
« Reply #73 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
andrew
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dreadnought72

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Re: Brushless Basics
« Reply #74 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.
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