[gpetilli]

I am bumping this thread since much of the motor basics are covered well and we hope to extend the basic concepts. Please excuse the thread hijacking.

For our off season project this year, we are considering experimenting with a poor man's Continuously Variable Transmission (CVT) gearbox. The basic concept is to use two motors but to intentionally mismatch free speed by about 2x. The 1st motor would be geared for high torque and would reach its free speed when the wheel was at 1/2 its top speed (lets call this the shift RPM). The 2nd motor would be geared for top speed. The PWM commands to the ESC for the 1st motor would be twice the value of the 2nd motor up to the shift RPM. The 2nd motor will continue increasing PWM values up to full voltage at full speed past the shift RPM. We will have one of these gearboxes on each of four wheels.

We understand that past the shift RPM the 1st motor will act as a generator and load the 2nd motor. The question is how severe is this load? What if we set the ESC to coast and signal the PWM to zero above the shift RPM? Will the flyback diodes in the 1st ESC effectively still load the 2nd motor? Will this damage the 1st ESC (we have blown HBridge with flywheel shooters)? Is it better to continue to drive the 1st ESC to max voltage?

More specifically, what we are considering is:

1st motor: RS775 12:60 (32dp) 14:72 (24dp) direct drive 6" wheel ESC=coast
2nd motor: MiniCIM 12:72 (24dp) same 72T gear ESC=brake

So the combined available stall torque (before gearing) is about the same as a full size CIM. During a pushing match we would drive all motors at full voltage.

We have looked at JVNs motor combiner xls - it predicts favorable results, but does not solve this exact configuration. It appears to assume matched free speed and therefor does not appear to comprehend the 1st motor loading the 2nd motor.