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Stepper or servo motor - controller design.

Endre Furnes

Sep 24, 2014
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I'm not sure if I put this in the correct forum, but help is needed. Anybody familiar with small rotary actuators?

I have been reading up and down on the net, trying to figure out whether I need a servo motor (with enclosed feed back like RC servos) or a stepper motor.

I shall turn a 42 mm dia knob with a belt drive some 80 deg end to end. No significant load as it is just a pot.meter with a off function at the anti-clockwise end. My input signal available is analog, 0 - 5 V, 0 - 10 V or 0 - 12 V, - free of choice. A position of the motor shall correspond to a voltage value. Speed is not important. I need to define end positions, though.

My space available is 50 mm in dia and 50 mm in depth. Shaft end flange.
As this is a hobby project, I was hoping to build the controls myself if it's not too difficult. I have been reading an watching videos on controller designs for both servos and steppers based on the 555 timer.

The servo control is said to be 'flickering'. Does the stepper need a separate driver circuit in addition to the controller circuit? I am feeling so insecure on all this, I found it's best to ask for experienced opinions.

Best regards
 

Harald Kapp

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Nov 17, 2011
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In my opinion a stepper is overkill for this application.
A servo can do the job. You will need a voltage-to-PWM converter to create the servo control signal (PWM) from the analog voltage. A servo will have a dead-band, which means that once is has stopped (position reached), it will require a comparatively large change in the PWM signal to start turning again. This is to avoid permanent activity of the servo due to small changes (jitter) in te PWM signal.
 

Endre Furnes

Sep 24, 2014
15
Joined
Sep 24, 2014
Messages
15
In my opinion a stepper is overkill for this application.
A servo can do the job. You will need a voltage-to-PWM converter to create the servo control signal (PWM) from the analog voltage. A servo will have a dead-band, which means that once is has stopped (position reached), it will require a comparatively large change in the PWM signal to start turning again. This is to avoid permanent activity of the servo due to small changes (jitter) in te PWM signal.

Thanks a lot Harald..
I got more and more confused the more I red, so it really helps me a lot just to narrow down to a servo motor. I assume (as I also indicated) that 'servo-motor' in this context is the small types used for RC controls ... ?

A dead-band would not concern me the way you describe it, but I am hoping for more precision on end positions. Would the 'dead-band' be something I need to build in to the controller, or is it incorporated in the motor itself?

Best regards
Endre
 
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