# Omni-wheels RPM

I need to figure out the RPM for a 4 inch omni wheel. Any suggestions? I have a skills day next saturday, and we are really crunching for time

Theoretical or actual?

The theoretical RPM of the motors are 100RPM for torque, 160 for speed, and 240 for turbo internal gearing. Then multiply that by the external gear ratio if you have one.

If you want to know the actual RPM, measure the speed that the robot travels at (drive a set distance and time it), convert it to inches per minute. The 4" wheel has a circumference of pi*4 inches. So the RPM = speed of bot (in inches per minute) / 4pi

Keep in mind that if you’re using the above calculations for guessing distance in an autonomous program, it’s not a linear relation between input speed (0-127) and output rpm, so be careful if you’re not running the motors at full speed. That’s why encoders are so useful. If you’re tight on time though, you can possibly use this data we collected to calculate the distance at whatever speed you’re running your wheels at. The data is for torque/default geared motors.

Average speed = distance / time

Or slap an IME on a wheel motor and use getMotorVelocity to get an RPM.