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        Cool Grayson Hobby MicroJet V3 rewind

#1 C₄H₁₀ May 28, 2012 12:09 AM

Grayson Hobby MicroJet V3 rewind
 
This weekend I acquired a burned-out Grayson MicroJet V3 motor. It's a little 39g, 28mm outrunner that's identical to the Suppo/BP 2208 line of motors, but rather than orange anodizing it's just silver all over.

I've been wanting to rewind one of these little beasties for awhile. I've got four of the Suppo 2208 motors in various stock winds, but they all run perfectly and there's no sense in tearing up perfectly good motors. The MJV3 came as a lovely, if damaged, addition to the herd.

The motor has twelve stator poles, fourteen magnets, and was wound with eight delta-terminated turns of what appeared to be a five-strand bundle of 30AWG wire. It is claimed to have a Kv value of 2200 in its stock form.

Taking apart and unwinding the motor was an uneventful process. No major trouble was anywhere to be found and the stator remained green and solidly coated. My initial plan was to rewind it back to factory specs, but a conflict of available wire gauges made this difficult.

I eventually settled on a double-strand, eight-turn wind with something like 28AWG wire. My wire is all salvaged from transformers so I don't know exact sizes, but it's right around there. I did a classic dLRK wind terminated delta and soldered up some connectors. She tested well but got very hot for my tastes. I suspect I missed a few turns here or there. The motor was obviously very aggressive in the Kv department as well; this thing was seriously cranking and drawing about 2.00-2.10A with no load.

I tore that out and tried a softer 10T single strand wind with what appears to be 26AWG wire. There's a tad less copper on the stator than I'd like, but it's very acceptable. This one ran smooth and cool, drawing about 1.5A unloaded and 12.5A at 10.91V with an APC 5x5. Thrust and RPMs seemed decent, but I have no formal test results for those. I'm guessing this will be a 6" prop motor for some quick wing or parkjet. By comparison, a Suppo 2208/12 (1800Kv) draws 9.5A and spins noticeably slower.

I figured it wasn't gonna get much better, so I chopped off the ugly magnet-wire leads and replaced them with soft black fine-stranded silicone wire. With heatshrink over the solder joints they just barely fit out of the motor's backplate.

It's a heck of a pretty little motor now. My math estimates the Kv to be around 2000 or so and the current it's drawing with a 5x5 seems to support that, but there's some confusion with the numbers so I'll have to triple-check.

The best indicator of success is in-flight performance, though. I'll see what it can do in that department within a few days, hopefully.

I might post some pics of the motor if I can get my camera ducks in a row :rolleyes:


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