Regen controller for E-Start on ICE

Looking to design and add and e-start function to my mx bike, Yamaha YZ250. My plan is to use something along the lines of a BLDC from an rc car as the starter motor/generator. I'm wanting to be able to hit the start button on my handle bars, start the bike, then once running the engine turns the motor to put power back into the battery and run headlights, taillight, radiator fan, and another accessories that I may add. Any suggestions on a motor controller that is small and can do this?

Do the small kids electric hoverboards or scooters have a controller that would work? Or anything along those lines?

Thanks

It's a really nice idea in theory. The dream of every engineer: combining multiple functions into a single mechanism.

Sorry this doesn't answer your question, but...

The main problem is that for a starter motor, you need relatively high torque at low speed, which means gearing the starter motor down (high speed small motor in -> gears -> slow speed high torque out). I.e. The starter shaft is spinning much faster than the crankshaft. And the starter output speed is optimised for cranking the engine (~idle speed). It doesn't run any faster than that.

For an alternator/generator, you want high speed low torque (maximum efficiency). I.e. The alternator is spinning at crankshaft speed. Which is why many motorcycle engines use stator coils powered off one end of the crank. It needs to operate up to the full engine speed.

The two devices have almost opposite requirements, so to combine both into one device would mean significant compromise.

Not to say that it can't be done, but if it was an effective method, we'd be seeing it in production bikes.

My advice would be to look for a current production engine with a similar system, and take some cues off how they solved the problem.

Presumeably the bike already has a 12 v battery and generator to power the lights and maintain the battery ?
Why not just focus on sourcing a 12v starter system from a similar bike and upsize the battery if necessary.

A starter from a similar model would be by far the simplest option, even if none are available a flywheel to match the crankshaft taper with the gear/sprocket and sprag clutch should be possible as manufacturers tend to use the same taper across the range.

Failing that it's possible to use the flywheel generator as a starter motor (RD125 twins are one example). That should possible with a large capacity generator but it will be a lot of work, probably a rewind, hall sensors, heavy phase wires, etc. etc. Not worth it imo, the heavier flywheel, controller, cables, batteries etc could add up to an extra 10kg and could swallow up $1000 fairly quickly, I'm fairly sure changing bikes to something with electric start would work out far more cost effective.

You can go further and build a SHVS system, with what you want you're almost there:

[youtube]r-5ql8Z5YrM[/youtube]

So I have made a spreadsheet that I can input BLDC parameters into such as kV, W, A, gear reduction, rpm, etc... and get out the rpm for the BLDC, AC and DCrms voltages, and I think I can source a BLDC to handle the rpm’s on both sides of the problem, in theory at least, I just can’t get enough voltage back out to get above my pack voltage, 3-4S li-ion. Is there a way to bump up the voltage at the expense of amperage? Also, what happens when I spin a BLDC above it’s kV x voltage value? I know mechanically it should hold, just not sure what happens with wattage.

Unfortunately, being that my bike is intended originally to be on a motocross track, it’s electrical system is pretty bare. Produces just enough power to run the ignition and that is about all. Aftermarket options, the few there are, don’t offer much above 30W of auxiliary power.

Good to know about the taper being similar across the board. I have definitely looked into adopting the starter system from a KTM two stroke model, but just as serious Sam mentioned, why not try to integrate two systems into one.

That Suzuki system is pretty sweet! Thanks for sharing.