What RPM for servos?

[jpsexton]

I found a deal on some servos but they come in a bunch of different rpms from 325 to 2100. What should I be looking for?

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[HuFlungDung]

Hi JP

You will likely want the highest rpm, maximum torque that you can find. Whatever your servo's maximum recommended rpm is will be the upper limit on your machine's speed.

On a 5 thread per inch ballscrew, a 2000 rpm motor will give you 400 inches per minute maximum feedrate, if you run the motor at a direct 1:1 ratio

That may sound like plenty, but if you have to use a 2:1 reduction from the motor to the screw, then you've got 200 inch per minute tops. Use a 10 thread screw, and you are down to 100 inch per minute.

You also need to know how many encoder pulses per second your controller can read. This will also affect the top speed that the motor will actually run at. To know this, you need to know how many pulses your encoders will be rated at. A typical 1000 line quadrature encoder can likely put out 4000 pulses if the controller reads the start and end of every pulse.