E-gebe

[Pezz]

Reading Matt Shumaker's site. He put a fan on his motor to assist with the cooling. Heat kills electrics.

That bike of Matt's is art!!!

 

[split_yer_wig]

fan would be a great idea....how much more juice would that pull out of battery?how much more juice would it pull out of wallet?

 

[MX21]

My point was, it seemed like the motor was getting hotter than it should, considering I was only peaking at about half the rated amps and averaging only 25%. Maybe getting out of sync like that causes all the current to generate heat instead of rotation.

MX

 

[split_yer_wig]

updates?

 

[MX21]

Since the motor threw a magnet, I've sent it back to get repaired/replaced. Still waiting on that.

MX

 

[split_yer_wig]

i bet the gebe system would accomodate an e-tek nicely

 

[oldschool]

MX, the loss of sync/internal slippage will heat you up pretty quick, but you won't really see it in the amps - you've got amps going to heat instead of propulsion. If I followed you right, you're at about 5000-5500 rpm at 30 mph, so 1600 at 10 mph. Thats a little below what the sweet spot is for most DC motors, but not too low. I didn't see anywhere what voltage you're putting in. If I read right, the motor will take 100 amps or 44.4 volts. But 100A at 44V would be 4.4kw, and the motor doesn't look big enough for that to me. I'm new here, but a bit of a wirehead. I plan on building an electric too, let's get this sorted out.

 

[MX21]

Yes, it's a 12-cell Lipo pack with nominal voltage of 44.4v. The motor is rated for 12-cell lipo and 100 amps.

 

[oldschool]

So at 25A average and 50 peak, you're pulling roughly 1100 and 2200 watts. That seems really excessive to me, as lots of rides do 30 mph with 500W motors. I was thinking of trying a 250W dewalt 12v at 18-24 for my roadie. I know it'll only be assist, buy hey, I need the exercise and I've got it and bunches of liion laptop batts.

But seriously, I looked over Matt's site you linked - hes calculated at 290 watts average in his last update, if I figger right (14.5 W*hr/mile * 20 miles/hr = 290W). and he's geared down pretty good to keep motor speed up, with a bit of a fan at motor speed if I scanned it right.

I like those motors, really efficient, but the RC guys don't post torque-power-speed curves like the industrials I 'm used to dealing with. DC motor current draw is highest at start and drops with rpm. Lots of the high current at start goes to heat - maybe you're off on the motor speed at cruise?

On the sync issue, you're using backEMF for speed sensing I think. Most motors tied firmly to moving machinery where inertia controls speed and the controller follows and adjust use hall sensors or encoders to track the actual rpm. Was the ESC guy saying you're adjusted as far as possible on the backemf following?

I know the new backemf controllers are way better than before, but maybe they're not there yet. Matt seems convinced they are, yet needs a slipper clutch to keep from breaking parts. He's a sharp guy, so that tells me it's more than just being throttle happy. If the throttle was too touchy, he'd reprogram it.

 

[MyPC8MyBrain]

Awesome build !

I am considering a similar adventure.. belt driven RC motor setup.

How did you connect the drive gear to the motor shaft ? I think once I get that ironed out, im going to start mapping this project out!

In figuring out gear ratios.. is the wheel ring 260 tooth vs the 11-14 teeth available on the motor gear ? so the 14 tooth gear would yeild 18.57:1 final drive ratio ?

Which drive gear did you end up with ?

Thanks!
Don