# How to figure out if motors can take a specific gear ratio?

I’m building the flywheel right now and I’m trying to figure out the best gearing for it. If I have the gear ratio of 3:112 which outputs 7467 Rpm, would 2 V5 200Rpm motors be able to spin it? I’m asking because when we had V4 120 Rpm motors, they would trip the breaker and stop while accelerating the flywheel, and if V5 200 Rpm motors have less torque than the 120 Rpm V4, it would struggle even more? I don’t know if torque has anything to do with the acceleration of the actual motor tho. And since 200 Rpm V5 has 80 more Rpm than V4 torque motor, its a 2/3 increase from the amount of rpm that we had.

P.S. We are using 2, 200RPM V5 motors for the flywheel

Your motor stopping problems are less about motor power and more about the heat generated while ramping up. At full power, a 393 wants to be doing at least 2/3rds of its free spin RPM, which is about 67rpm for high strength gearing (100 rpm free spin). While your wheel is accelerating, you would need to limit your 393 motors to under full power so that they aren’t at low RPM and full power, which is the scenario that generates the most current and heat. I would include an encoder somewhere in a 393 flywheel system so that the program could see what the RPM is and adjust motor power appropriately.

V5 motors are more tolerant of heat abuse largely because they self-limit their current draw. If you ask them for full power at 0rpm, they instead refuse and only provide partial power until their speed increases. 393 motors do not have that functionality built in, so the programmer has to provide it for them. In other words, V5 motors limit their torque output to a fixed value so as to help avoid overheating. For your V5 system, you might notice it accelerating a bit slower, but as long as you aren’t spending all your time ramping your flywheel speed up and down the motors should be quite happy.

As for your physics question, torque is related to angular acceleration in a similar manner to force and linear acceleration: torque is equal to rotational inertia times angular acceleration. It mirrors the linear force equation of F = ma.

@John TYler

That makes sense thank you.

If I add slew rate to a v5 motor, would that help the case? Because what I’m getting from this is when a v4 tried to go from 0 to 120 rpm and was below 67 rpm it would shut down, slew rate could help that. For v5 if I try to go from 0 to 200 and it can’t it’ll lower the power input until it can. So slew rate could make it better. As to torque, I’m getting that it has nothing to do with acceleration right?

Torque is proportional to rotational acceleration. Double the torque, double the acceleration. Halve the torque, halve the acceleration.

For V5 motors, if you find they are consistently getting too hot, you can actually have them set a lower power limit than the firmware-specified maximum power limit. There are three overloads of the

``````
setMaxTorque

``````

method for the motor class in Robot Mesh Studio and VCS to do this:

``````
setMaxTorque(double value, percentUnits units)

``````

;

``````
setMaxTorque(double value, torqueUnits units)

``````

; and

``````
setMaxTorque(double value, currentUnits units)

``````

. From there, the motor firmware will do what it can under those constraints to meet the target velocity you give to the motor. There’s no fancy coding that you have to do in the user program to make that happen, which is what slew rate code does for 393 motors. The firmware’s power limit accomplishes the same purpose.

@John TYler Thank you very much