Newsgroups: comp.robotics
Path: brunix!uunet!utcsri!skule.ecf!hertz
From: hertz@ecf.toronto.edu (HERTZ ROGER BARRY)
Subject: Re: Stepper motors
Message-ID: <C4tBM3.HtB@ecf.toronto.edu>
Organization: University of Toronto, Engineering Computing Facility
References: <1pdah8INNqdc@dns1.NMSU.Edu>
Date: Thu, 1 Apr 1993 16:10:50 GMT
Lines: 36

In article <1pdah8INNqdc@dns1.NMSU.Edu> mcole@scotty (COLE) writes:
>I am having trouble driving a stepper motor.  I am driving each of the  
>phases with an IRF510 FET.  At around 1KHz the motor just sits there and  
>hums.  Any suggestions?

Hmm.  Could this be what is referred to as `stalling'?  I don't have
a whole lot of practical experience with this, but I know it is a
unfortunate characteristic with most stepper motors.  

The motor `stalls' or skips steps when the step rate coincides with
the natural frequency of the motor.  I've seen it in both real motors
and in simulation, at frequencies close to what you are describing.

One suggestion I have heard to overcome this problem is to avoid this
frequency as much as possible; either by going through it quickly
or never reaching it at all.  Kind of seems like a cop out, heh?

Another suggestion involves adding more damping to the system, so
as to reduce the detrimental effects at the fundamental frequency.
This can be done in one of two ways: 1) adding mechanical damping
to the motor shaft, or 2) using a fancier driver that dissipates
energy from the motor.

You may also alter the inertia of the motor/load to put the natural
frequency at a more convinient place.

Does anyone else have practical experience with the above
techniques?

Hope this helps.

Roger Hertz

hertz@ecf.toronto.edu
University of Toronto
Institute for Aerospace Studies
