chessguy103 said:
You're saying that as long as long as it has the right power and rpm, then torque can be manipulated to be whatever I want, right? Just want to make sure I understood correctly.
Yes.
Let me help you visualize the concept, looking at the following figure for a motor for an electric bicycle:
The
orange line is the wheel power, i.e. what you actually need. Usually the sum of the rolling resistance, aerodynamic drag, etc.
The
blue line is the actual motor output. Where it meets the
orange line is where the acceleration is zero. Thus it represents the maximum possible speed (25 MPH, in this case).
The
red line is the actual electric power required by the motor. You can see that at low RPM it is really inefficient to convert its electrical power to mechanical power.
The
green line is the motor efficiency, i.e. the
blue line divided by the
red line. Note how in this case, the peak efficiency is past the maximum speed, i.e. it will never be reached.
Normally, you would want your vehicle to be driven in the region between peak power (for best acceleration) and peak efficiency (for cruising speeds). Imagine this motor used on your vehicle with a top speed of 15 MPH, you would constantly be at very low efficiency (wasted heat). And the fact that in that speed range you have so much more power than you need (compared to the
orange line), it might even be less efficient since you will have to constantly reduce the motor power output by a large amount (say, cruising at 10 MPH).
But if you would use the same motor with a gearing factor of 2, the
orange line would remain the same, but all other lines would shift to the left. So peak power would be at around 6 MPH and peak efficiency would be at around 14 MPH. The
blue line would cross the
orange line at around 17 MPH, i.e. the new maximum speed.
Here is another similar graph for bicycle electric motors:
You see that for any company, they have their peak power in a similar RPM range, because it matches the efficient human cadence range (60-110 rpm).
