Servo default speed

Lynxmotion Electronics & Software
1

Hi,

I was wondering what is the default speed rate for a servo motor when the “S” parameter is not specified?

Thanks,
Stephen

2

As fast as the servo can move.

However if you use the T command the SSC-32 bases the move on a time value. It will move the servos from where they are to the new destination in the amount of time in the T command.

#0 P1000 #1 P2000 T 2000

This command takes 2 seconds to complete. Remember the servos used must already by activated and holding a position before the T command will be recognized.

3

I’m using the HS-475 servos and the spec states:

0.18 s per 60 degrees @ 6V

If my math is correct:

180 degrees / 2000 units = 0.09 degrees / unit

60 degrees / 0.18 seconds = 333.3 degrees / second

(333.3 degrees / second) / (0.09 degrees / unit) = 3703 units / second

So “3700” would be the fastest rate for this particular brand of servo correct?

Which means any “S” value between 0-3700 would affect the rate, and any higher would have no effect correct?

Thanks,
Stephen

4

The default speed if no S command is used will be the maximum value (65535). This is the speed at which the SSC-32 output pulse will change, which may exceed the maximum move speed of the servo itself. A speed of 65535 is effectively an instantaneous move.

I agree with your math. Based on the servo spec of 0.18s per 60 deg, and the approximation of 180 degrees / 2000 units, all move speeds above 3700 will have the same effect. The exception would be if you sent a new move command before the previous one had completed. The starting point for the new move command will be the current SSC-32 pulse width. If the SSC-32 is changing faster than the servo can keep up, then the starting point for the new move command will be beyond the current servo position, and the servo will overshoot slightly. If this is an issue, then always specify a speed that is less than the max servo movement speed.