Motor Torque, RPM, andPower

VEX V5 General Discussion Technical Discussion
1

Okay, this might be a stupid question, but I’ve been looking at the torque and power curves of the 5.5W motors and 11W motors, and I have a question.

5.5W curves (from Vex)

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11W curves (also from Vex)

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In both of these graphs, the output power will drop after around 60-70% of the maximum RPM. This is also where current and torque drop. Is there a difference between running a motor at the maximum RPM, or running it at the maximum power point and using a theoretical gear ratio to attain the same RPM as the motor’s maximum RPM.

I know there would be losses due to the gear ratio, but would the losses be negated by the increased output power of the motor? Lets say you have 2 wheels being spun at 600 RPM by 2 sepreate motors. One is a 1:1 ratio with a 600 RPM motor spinning at the maximum RPM, and the second is a theoretical perfect gear ratio (the exact reduction) that, with the motor operating at maximum power, current, and torque, spins the wheel at the same speed as the first motor.

I don’t understand any of this, so I’d appreciate any input. Thanks!

2

Are you planning on setting a max rpm in the code? If the motor peaks at 60-70% of max rpm then if it has the same wheel diameter the wheel will be spinning 60-70% as fast. I’m not sure I understand the question though.

3

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When you are driving a F1 car, you want to keep your rpm at 5000 to 6000 by 8-speed transmission, because it has the highest power which has highest acceleration.

When you are driving vex robot, you don’t have 8-speed but 1-speed transmission. you want your top speed to be 100%rpm.

There is a difference:

600rpm motor, 1:1 gear ratio at 400 rpm is 0.35Nm.

200rpm motor, 1:2 gear ratio at 400 rpm is 0.2Nm.

losses due to the gear ratio will be negated by the torque, not power.

they are different thing, power=current*voltage=rpm*torque.