Last night I was mulling over how to how to determine the efficiency of a gearbox, and if my assumptions and math are correct, it's really easy:
- Get a value for the driving motor's free speed that you trust.
- Measure the free speed of the motor+gearbox and multiply by the gear ratio to get the motor speed.
- Divide this by the motor's free speed and square the result. This is the "power efficiency".
In cases where we have multiple identical motors in one gearbox (such as 2 CIMs on a drivetrain), we can treat them like one motor with the same free speed and twice the stall torque. The above method should still work.