CIM Quiz 2

[Ether]

Originally Posted by Jared341

I believe you are making the mistake of assuming the motors are providing their maximal mechanical power while spinning at their free speed.

What he did, I believe, is to pull the following data:

Cim @ 35 amps: .70 Nm torque, 230 W, 395 rad/s = 3770 rpm
Fish @ 35 amps: .260 Nm torque, 180 W, 686 rad/s = 6550 rpm

... from some 10.5 Volt motor curves that he has.

He then reasoned as follows:

- if 35 amps are supplied to each motor, they will produce the output power indicated above at the rpm's specified above (if his 10.5 motor curve data is valid, this is valid reasoning)

- the sum of the output power from each motor is then used to calculate how fast the impeller will spin, given that power

- that impeller speed is then used to calculate what the gear ratio must be for each motor in order for each motor to be spinning at its respective specified rpm when the impeller is spinning at the speed just calculated.

It's an interesting solution, but it's not the solution to the problem I had in mind because it requires that the current to each motor be controlled at 35 amps. The problem I had in mind did not involve controlling the current. As stated, each motor is being driven at a constant voltage (12V), not a constant current.