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I am in the process of designing a small generator that will use a permanent magnet DC motor to generate power to a battery. However, I am struggling to decide on the necessary gear ratios to optimally get the most out of the downward force that will be applied to the generator plate (people walk on it).

TLDR; is the torque required to turn a motor shaft the same as the torque it outputs at peak efficiency?

If not, how can I calculate the torque required to spin the motor at optimal efficiency (3000 RPM)?