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Jul 30, 2003, 06:55 PM
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KreAture's Avatar
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Discussion

Scratchbuilding a brushless motor...


I've found that to save some weight in some of my micro-models and at the same time get a better fit I'd make the whole motor myself.

Whad I did was to place 2 ballbearings in a hole in the (to be) firewall. Then I placed 6 pegs around the ballbearings and formed 3 coils on them. I thought I'd get a nice and light little motor by attaching a disc on the shaft and placing magnets on that disc. Turns out the EMF was way to low I think for my controller.

I measured and compared to a small cdrom motor and I get only 1/10 or less the emf.

I'm using a MGM 1812-3s. They do not mention a minimum inductance nor any minimum back emf.

As my coils are coreless I though that maby making them cored may solve the problem ? Any ideas ? I added two small nails in one set of pegs that formed a single coil. Adding this nail increased the EMF from that coil 5 times

Here is two piccy's so you know what I'm talking about:

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Jul 30, 2003, 08:53 PM
Registered User
Try winding the coil directly around the nail. The wooden pegs are not good.

Toshi
Jul 30, 2003, 09:47 PM
DNA
DNA
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http://www.rcmicroflight.com/library/motor1.asp
Jul 31, 2003, 12:16 AM
Airplane Addict
Wow, that's really cool. I've been playing with CDrom motors lately.
I was wondering if you had access to any surplus inductors with ferrites cores. I think they use a purified iron or special alloys in them that would probably work, but at a weight penalty.
Jul 31, 2003, 03:31 AM
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Hmm, ferrite cores would probable be the best.
I'll see if I can get ferrite pinns
Jul 31, 2003, 04:39 AM
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I got ahold of some ferrite blocks and will try making the same 6 pole, 3 coil, 4 mag motor with them.
Jul 31, 2003, 05:54 AM
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Success!!! It actually runns!

I will be posting pics and a video soon, just gotta tweak it a bit
Don't know how effichient it is but weight seems way down compared to a normal cdrom motor.
Jul 31, 2003, 06:07 AM
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Well well. That got hot

With only a total of 40 turns of 26ga pr coil (20+20) it turned out to be more of a bbq than a motor
I do think I'm on to something here though. The controller managed to rev it up a few times. It seemed the back-emf wasn't strong enough to limit the excessive currents but I am on the right track.

Thinner wire and a lot more turns seems to be the way to go.
I think I'll rewind this one before posting anything. IT looks like a real hackjob now anyways...
Jul 31, 2003, 07:21 AM
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Hurray! I had a top-lid here from one of those wierd cdrom's with only a flat plate-motor and coils just glued to the pcb. (This was where I originally got the idea.) The plate has 8 magnets 3mm thick and when I tested it with my fist coil I got a whopping 70 mV! As good as with the rewound cdrom!

I'm now winding the last two coils and am very looking forward to the results. (I will be trying the motor with the 8 pole first, then try and make a 4-pole later. 8-pole should give more torque though so I may be staying with that.)
Jul 31, 2003, 08:24 AM
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Well! It works!


It has very strong cogging using the 8-magnet head but man is it strong ! It revs up with NO jitter at all. Going to take some power-readings now.

Will post images and video soon.
Jul 31, 2003, 09:59 AM
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Success at last!


Using ferrite seemed like a very good idea

Here's a series of pictures showing my little baby in the making:



First I started with a 20x30mm piece of ply made by sandwitching two 2mm balsa pieces. I added two ballbearings in the middle (for 3mm shaft) and cut pits in it to fit the small ferrite bits I had. All bits were about the same size and I made sure they were same height over the ply. Glued them in place with CA.



Now came the agony! I had to get enough windings on there and I was determined 40 turns on each peg was what I wanted.
I used 0.3mm wire (about 29 or 30ga) and managed to squeeze in 40 turns by making sure the first two layers were really neat and tidy and CA-ing them in place as I wendt.


Finally Done and all coils were finished. Hopefully with equal ammount of turns. (There may be +/- 2 turns or so as I really lost cound a lot or times...)


Here's the rotor The magnet was so strong that in combination with the cogging it shook loose one of the ballbearings. I had to reglue that. Is this ammount of coggin really good ?

Anyway... It draws 0.6 amps idle running at a whopping 17,600 rpm at half throttle (Using 2x LiIon cells) At full throttle I didn't have time to take a reading as it knocked loose the ballbearings again. I think the cogging is too much
Jul 31, 2003, 10:30 AM
Registered User
K,

Impressive. It gives a whole new meaning to "DIY".

Tony Turley
Jul 31, 2003, 10:48 AM
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I just wish I could get it to stay put.
The ballbearings keep coming loose
Jul 31, 2003, 10:54 AM
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Nice work....pulled an all-nighter did ya?...lol!

Drivie
Jul 31, 2003, 10:59 AM
Airplane Addict
Cogging is GOOD, it means your magnets are good and positioned nice and close to the stator. AWESOME.
Keep up the good work!


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