DIY 35mm brushless motor

[Prop-er]

Situation:

I came across a long 35mm stator pack from an angle grinder. I managed to split the pack up in pieces about 10 to 30mm long. Used a very big press to get rid of the shaft, in the centre of the stator.

I'm gonna try to make my first DIY brushless.

I want to use batteries and electrics, I already have.

My biggest pack of lipo's is 3S.
My largest ESC is 18 Amps.
My biggest copperwire for winding is 0,5mm.
I designed it around a rather small prop, the GWS 9x4,7.

So I want this motor to have a max. input of about 170W. That's 9550 rpm and about 1000 gr (35Oz) of thrust.

The stator has 12 teeth, and I want to use a LRK wind. (wind 6 teeth)

Calculation:

I used the torqman calculator 3.01 (http://www.torcman.de/konfiguration/Torcman_Konfigurator_301.xls) to get an idea of what to expect.

The tab "tm350 10pol" seemed a good place to start.

Stator length: 10mm
12 winds of 6 x 0,5mm wire WYE
Weight: 120 gr.

I used a 3D model of the stator & motor to get an idea of weight. It includes the weight of the copper. It's a bit on the heavy side, so changed it to:

Stator length: 5mm
22 winds of 3 x 0,5mm wire WYE
Weight: 70 gr.

Same power, but 50 gr less weight. Could still be lighter:

Stator length: 3mm
30 winds of 2 x 0,5mm wire WYE
Weight: 45 gr.

Now it starts to get about right. Nice weight, and still good power.

I searched around for 10 pieces of 10x3x2mm neodyme magnets, and found them at here (http://www.supermagnete.de/magnets.php?group=blocks_small).

According to the drive calculator (http://www.badcock.net/motorcalc/) tools, the bell ID will be 40,5mm, and I will make the flux ring 2mm thick, so OD will be 44,5mm. Airgap is 0,12mm. Magnet coverage is 88%.

According to the drive calculator, the winds are capable of max. 25A, so they will be fine.

But what about saturation in the very thin stator? Any thoughts :confused:

Results of calculation with Torqman Calculator (http://home.isp.studenten.net/user_vbru/35mm%20berekening%20uitkomst.PDF)

Results of calculation with Drive calculator (http://home.isp.studenten.net/user_vbru/35mm%20berekening%20uitkomst2.PDF)

http://www.rcplans.nl/RC%20foto-album/35mm/1.jpg
http://www.rcplans.nl/RC%20foto-album/35mm/2.jpg
http://www.rcplans.nl/RC%20foto-album/35mm/3.jpg
http://www.rcplans.nl/RC%20foto-album/35mm/4.jpg
http://www.rcplans.nl/RC%20foto-album/35mm/5.jpg

[olmod]

Nice graphics there :) as you may have read in olmods motor build part one there are a few of us that like those stators ,have you tried to wind that many turns of 2 strand .5mm yet? from memory it might not be possible to fit it all on and you may have to go for a single thicker wire ,
insulating the stator poles is a problem and i think it would pay to have a look at powerditto's site he has a wealth of experience, ill be very interested in your progress,cheers Lez. :)

[Prop-er]

Hi Lez,

Thank for you response. I'm glad you like the renderings.
I've simulated the windings in 3D. 30 winds 2x 0,5mm is (easily) possible:

http://www.rcplans.nl/RC%20foto-album/35mm/6.jpg

I will look into isolating the stator. I saw one yesterday with red painted front and back, and using stiff plastic sheet to isolate. Looked really neat.

[olmod]

That explains it well. :) i thought distributed wind ''Doh'' if you have a friendly motor winder in your area they have a great selection of fish papers and other insulators that can be cut into strips on a photo trimmer,ive tried grinding with a diamond point in a dremel all the corners and then coating with epoxy with mixed results and dont consider it worth the effort.if you can find a suitable size thin walled heatshrink and cut short lengths about 2`3mm oversize to fit over the stator pole then shrink it ,it works every time ;)
cheers :)

[Prop-er]

That's a very good tip. I will try the shrink trick!

I'm a bit concerned about the sheer amount of copper around that very small stator teeth. The teeth are only 2mm wide, 3mm thick. The layer of copper is around 4mm thick.

If saturation would occur, would thinner magnets be a solution?

Maybe I will just start building it, and see what happens.

[olmod]

Less turns would help, the only time id go for that many is for large props,but try it ,ive had little to do with LRK's, it would not take long to rewind anyway :)

[powerditto]

:confused:

[Prop-er]

Ouch....

I punished myself by changing the model, and painstakingly added all the 6 poles 30x double 0,5mm winds......

http://www.rcplans.nl/RC%20foto-album/35mm/8.jpg

http://www.rcplans.nl/RC%20foto-album/35mm/9.jpg

http://www.rcplans.nl/RC%20foto-album/35mm/10.jpg


;)

[latrans]

Prop-er,

Your drawings are excellent, but if you plan to use them as a model for your motor then I think that you need to be realistic about how much room your windings will take up. The way you have them drawn above is a little, er ...... optimistic. Not trying to discourage, just help. Good Luck.

Latrans

[Prop-er]

Thanks, Latrans. No worries, I will keep at least 5mm room both sides of the stator.

After all, a 3D model doesn't always represent the final work drawings, you know...

I've nearly broken my brain over trying to design a 20 gr. motor doing 400 grams of thrust (14 Oz) on 2 cells. It's near impossible.

Single 20.2mm stator, not enough power.
Double 20.2mm, too much weight.

Maybe I'll find the sweet spot with a 25mm stator. I'll order a couple.

[olmod]

Single 20.2mm stator, not enough power.
Double 20.2mm, too much weight.

Maybe I'll find the sweet spot with a 25mm stator. I'll order a couple.

mmm ive had the 20's doing over 400g thrust @14amps on 2sp. 108 w
but they are about 22~24g heavy. so dont give up :D

[Prop-er]

That's interesting, Olmod!

Can you tell me how many turns, stators, what wire diameter and prop you did use?

Or can you give me a "direct hit" search key for your two threads?

[olmod]

PM sent , ;)

[Prop-er]

Look-o-look what the postman brought me:

http://www.rcplans.nl/RC%20foto-album/35mm/DSCN1526.JPG

1. Copper
2. Two 3mm titanium shafts (very, very light)
3. Magnets
4. Bearings

I've sourced a place where they sell Aluminium Ø50, I'm planning to pick it up tomorrow.

[olmod]

What not mag alloy? :D nice shafts who is the supplier?

[Prop-er]

I bought them here: http://www.modellbau-letmathe.de/

They even added a free chocolate Santa!!! ;)

[olmod]

That was nice of them :D
the next time you want to get laminations from a angle grinder motor ,just cut through the shafts about a cm from the laminations with a cutting blade in a angle grinder ,then place it in the chuck and drill/bore out to 12mm id
then either use a gas torch or throw it on a fire,it will burn out all the insulation and the wires come out super easy,the fire wont hurt the laminations as it softens any residual work hardening done in the pressing. ;)
ive done quite a few and believe me its the best way not to mention quickest.

[Prop-er]

http://www.rcplans.nl/RC%20foto-album/35mm/alu.jpg

I've got a 5" long piece of 2" diameter aluminium. Paid € 10,- (17,50 Austr. $) for it. I hope it will be long enough for a couple of motors.

Thanks for the "burn that winding out" tip! I will first try to pry them out, since my (first) stator is only 3mm long.

:)

http://www.rcplans.nl/RC%20foto-album/35mm/DSCN1540.jpg

[flarssen]

According to the drive calculator (http://www.badcock.net/motorcalc/) tools, the bell ID will be 40,5mm, and I will make the flux ring 2mm thick, so OD will be 44,5mm. Airgap is 0,12mm. Magnet coverage is 88%.

The airgap will be 0,75mm. According to the experts, it doesn't matter if the air is between the stator/magnets or magnets/flux ring. At the center of the magnets, you will have 0,12mm between stator and the magnet but you have 0,63mm between the magnet and the flux ring.

I just finished a motor based on a similar stator:
LRK 3410 (http://www.rcgroups.com/forums/showthread.php?t=459618)

Good luck with your project!

Fred

[olmod]

I bought them here: http://www.modellbau-letmathe.de/

They even added a free chocolate Santa!!! ;)
Have you already made your flux ring ? if not may i make a suggestion ? for the type of magnet.

[Prop-er]

I nearly finished the technical drawing. The steel flux ring will be just as thick as the magnets. Please advice me on the design of the ring!

I'll be using 8x4x1,2mm, N50M Magnets. They cost next to nothing, so if you think there's some efficiency to gain, I can still buy other magnets.

Maybe I'll try to fill the area between magnets and flux ring with some flux carying glue.

Today my dad called. He was visiting a company that sells all kinds of aluminium. He asked if I could use a 2" diameter piece of alu, about 10" long.
Sure dad!

Should have enough alu for 2006...

[latrans]

Prop-er,

I would say that for a motor of this size you would want to use larger magnets than 1.2mm, 2mm would probably be appropriate. As for the flux ring the thickness depends on the thickness of the magnets to be used but as a general rule the flux ring should be about half the thickness of the magnets so if you were to use 2mm thick magnets a 1mm thick flux ring would work well.

Latrans

[Prop-er]

Thx Latrans.

I might take your advice. Need to sleep a night on this one.

I'll make the fluxring 1mm thick.

[olmod]

I have made my flux ring for the 4520 and im setting it up with curved magnets origonally designed for 22.7 stators from www.strongrcmotors as an experiment :) i thought at first there was going to be a mismatch between the radi,but when placed in position and held up to the light it was ok,sometimes you can be lucky :) i mean by rights it should not be a fit :confused: the magnet thickness is nominally 1.4mm x 10mm ,im end to end joining to get the 20mm magnet length. cheers. :)

[Prop-er]

I looked at my Mpjet red motor this morning. It's basically an 28mm, 160 watt, 50 gr LRK. It's got 2mm mags....So my LRK3503-30W gets 2mm also.

Bring on the new 2mm mags!

[ecologito]

Very nice data, I am also working on a 35 mm stator motor. I just finished turning my flux ring and end bell. I replaced the metal stator holder, and turned an aluminum holder. I found 7.0mm OD and 3mm ID bearings. I will post pictures as soon as I find my camera ( took the pictures but dont know where I left it).

[Prop-er]

It's been a while since my last post.

I've been thinking why I would like a motor like I've described and designed. I simply already have a motor like that.

My SU-27XXL could use some more power and speed, though. So, back to the drawing board. New specs:

Battery: 2S 1250HD Kokam. (15C / ~ 19A / ~130 watt)
2500 rpm/v
Power: 100/120 watt (mech/electr)
GWS HD 7x3,5
15700 rpm / 66 kmh / 680 gr
14 magnets 7x6x2
12 winds 5x0,5mm
Rotor inside diam. 39,7 mm, 1mm thick.
Statorheight 6mm

Drawings are finished. Work can finally begin. Need new magnets (again...) :o

[Prop-er]

Look at what the turner brought me:

http://www.rcplans.nl/RC%20foto-album/DSCN1912.JPG
http://www.rcplans.nl/RC%20foto-album/DSCN1914.JPG
http://www.rcplans.nl/RC%20foto-album/DSCN1915.JPG
http://www.rcplans.nl/RC%20foto-album/DSCN1916.JPG

Mags are on their way. Can hardly wait...

[Prop-er]

It's been a while.

I've had one week of skiing in France. I took the stator and wires with me, and actually found some time to wind it.

Winds aren't nearly as neat as I would like. Worst of all, all wires seem to be shorted against each other, and the stator...Bugger.

I've used distributed wind with 6 turns of 3x0,63mm wire. I found it very hard to wind these parallell thick wires. I think I will buy some 1mm thick wire, and use Olmod's tip to apply heat shrink tubing over the stator teeth.

[ecologito]

looking great, I am trying to buy a lathe so I can turn my parts ( and not wait to borrow one).

[Prop-er]

Oh yes, a small lathe would be a great addition to the machine park... But for now, asking a craftsman to to the job for me will do...

I fixed the earlier pics btw.

[Prop-er]

http://www.rcplans.nl/RC%20foto-album/35mm/DSCN3682.JPG

It took me allmost two years to finish this motor! But it is now finally ready to go, and runs great.

I've wound it with two 0,5mm strands parallel (which is equal to one wire of 0,7mm) 8x on all 12 poles. 4 winds up, 4 winds down. Distributed LRK.

All my previous winds produced stator shorts. Before winding this one, I covered all theeth with shrink wrap. This worked great (efficiency might suffer a bit).

http://www.rcplans.nl/RC%20foto-album/35mm/DSCN3687.JPG

I connected my ESC to the sixth 500mA port my Robbe multi charger 6. The ESC would engage properly, the startup sounds as usual, but it wouldn't run. (the charger lowers the voltage as the Amps increase)
I then connected a trashed 4,8V NiMH battery. Same effect. (battery couldn't deliver the amps) By now I was certain there where no shorts, and connected a lipo. It run right away! Boy was I glad!

It runs a APC 5,5x4,3 at around 20.000 rpm (I guess). Static thrust is 526 gram, WOT pulls 17A at a 3S lipo. Motor is slightly warm after running.

It's a decent 180 Watt motor, weighing 60 grams.

http://www.rcplans.nl/RC%20foto-album/35mm/DSCN3690.JPG

I'm going to mount this motor on my Sukhoi shocky, who's in need of some decent power from the first time i've flown her.

Video:
http://www.youtube.com/watch?v=tyWjdy_Q0yo

[Fourdan]

Hi
Good job, nice pictures
Now you have to communicate about performances:
Rm (in ohm) , via Ohm's law
Io(A), rpmo no load for two voltages
Then everybody could estimate
1) Kv rpm/V
2) Peakeff%
3) current for etamax
Weight is 60 g ?
Regards
Louis

[martseger63]

I noticed that the distance between thrust meter hinge line and the motor shaft is greater than the distance between hinge line and the screw that's pushing the scale. That will lead to false measurements of thrust, and you will get bigger numbers. Prove me wrong :rolleyes:

[Prop-er]

Bugger. You got me. :)

Normally the motor is mounted at exact the same distance from pivot to weighing scale. This time the motorshaft extended from the rear, so I had to think of a quick solution. Never thought about the implications....

Today I'm showing the motor to my colleague who did the metalwork. After that I will try to make complete and accurate measurements of this motor.

Prop-er

[Prop-er]

Did the thrust test again. 325 gram. :D

Took the prop off, hooked the 3S lipo and gently started the motor.
Measured amps full throttle. Whopping 15A.

Turned it off. Checked for free running. The back of the shaft was not clear of the PVC pipe. Adjusted the motor.

Did the run again. Again 15A. Suddenly smoke. End of my ESC. :D

This is the first time I've wrecked one. Boy does it smell.

How does one repair a smoked ESC? :D

I think you understand I suddenly don't think the numbers are that important.
Somehow I can't understand the 15A.

[Prop-er]

Fault was in the wires. Had some small servo wires between motor and connectors. This is not normal, I just was out of connectors, and quickly soldered these from an old Cd-rom to my new brushless. (it just a quick test, the new ones are ordered, blabla)

The heat during the no load tested melted the insulation, and a short occured, smoking the ESC.

Bad boy. Leason learned.

[flarssen]

There must be some other problems also, since 15A noload is far too high.
Try a generator test by spinning the motor in a drill and measure the AC voltages between all three wires. The three voltages should not differ too much.

Fred

[olmod]

Yep i agree it sounds like a short to earth.you could try heatshrink over the teeth trim after heatshrinking (not PET)