Gear ratios for launcher

[Ether]

Originally Posted by iambujo

So we just rechecked wheel speed, and it maxes out at about 3500 RPMs, or 12,991 RPMs motor speed. We measured the voltage across a .01 ohm power resistor and it was about 210 mv. So at max speed it looks like we are drawing about 21 Amps. In-rush current when the wheel starts up peaks out at about 50 Amps for a brief moment.

3500*3.67 is equal to 12845 motor rpm.

According to the motor curves,
An FP-0673 at 11.79 volts (= 12 - 0.210) and 12845 rpm should be drawing about 40 amps.

Since you measured the current to be 21 amps, let's use that data instead:

According to the motor curves,
An FP-0673 drawing 21 amps at 12845 rpm is getting about 9.7 volts. Add the 0.21 drop across the measurement resistor and your Jag is putting out about 9.9 volts. I'd expect it to be a bit higher than that, unless:

- your battery is weak
- you've got excessive resistance in your wiring or connections
- you're running a bunch of other heavy-demand stuff while you're running these tests
- the Jag is not putting out 100% PWM
- the motor curves are wrong or the motor you have differs substantially from them

Now we need to check the motor voltage, maybe that is where the flaw in the applied math is.

The math is sound, but the data or assumptions could be wrong. I agree it would be a good idea to check the voltage at the motor, to validate the above engineering calculations.

Everything is working ok, at this point it's just a study of the real world numbers we are collecting compared to the expected data based on the motor curves.

When the engineering calculations don't jibe with the observed test data, it could be a sign something is not right. I understand this doesn't necessarily apply to FRC, but in many engineering fields when the test results don't agree with the expected results based on calculations or simulations, you stop the presses and figure out why.