# How does gearing affect power generated by a permanent magnet DC motor?

I am currently working on a project to harvest electrical energy from a rowing machine. I am trying to make use of gearing ratios to adjust the resistance level offered by the system, and the impact it will have on the generated power. I plan to connect the flywheel of the rowing machine to the shaft of a PMDC motor by chain or belt.

I am looking at an RPM range between approximately 400 and 800 for the flywheel. If the radius of the sprocket attached to my flywheel was lets say 0.3m, and the radius of the sprocket attached to the motor was a smaller size, say 0.1m, I would expect a greater number of RPM in the motor shaft. However, what would I expect in terms of the power generated by it, and the resistance against the mechanical force applied by the rower?

Also, is there a maximum counter-torque I would expect from a given motor, for example if the gearing ratio was adjusted so that more torque was being applied to the motor than it could provide counter-torque? I've noticed that motors are rated by their motor torque. Is the maximum counter torque equal to this value? What would happen if it was exceeded? Would no additional power be generated?

Sorry if the question is a little vague/factually inaccurate i can try to add any additional information needed. This is all very theoretical at the minute, just trying to gain some understanding.

• Usually maximum torque is at its maximum power rating so I don't think you would want to generate more power out of a motor than that. also technically any transmission or anything will be a source of loss. Apr 18, 2020 at 14:58
• You don't want the generator to provide as much counter-torque as you have being applied by the rower. If they were equal it would be impossible to row. Apr 18, 2020 at 15:18