# How to calculate power genereated from motor

Can someone help me work through the math in choosing a generator.

I have a pedal bike that I want to extract power from. From another member here the dream is to make something of an electric “fixie” bike. No batteries, just a motor and a generator with a small power buffer.

My initial idea is to embed a brushless motor into the crank set. Super compact and unassuming. Plus another hub motor at the back. Avoiding gears and complicatedness is the goal.

The target numbers for the generator are to pull 200W at 60-80rpm cadence (Optimal Pedal speed).

How can i calculate how this motor will perform at 80rpm? Given the advanced ODrive controller, how much power can i extract from these specs?

Can I just go ((80RPM / 150Kv)^2 / (0.039 ohm per phase)) * 3 phases = Peak 22W @ 80RPM?

You’ve just calculated your waste heat at 80RPM I think(?)

If you’re putting 200W into the motor at 80RPM, you’re generating some 24Nm of torque. To get a resistive torque of 24Nm, you’ll need to put something like 1000A through the motor lol. I think you need a ~30:1 gearbox or a much lower Kv (rather, higher Nm/A) motor.