Newsgroups: comp.robotics
Path: brunix!uunet!europa.eng.gtefsd.com!howland.reston.ans.net!usc!cs.utexas.edu!csc.ti.com!tilde.csc.ti.com!mksol!strohm
From: strohm@mksol.dseg.ti.com (john r strohm)
Subject: Re: Stepper motors
Message-ID: <1993Apr6.142554.11485@mksol.dseg.ti.com>
Organization: Texas Instruments, Inc
References: <1993Apr1.181351.18276@magnus.acs.ohio-state.edu> <64@mlb.win.net> <1993Apr5.213803.10285@phx.mcd.mot.com>
Date: Tue, 6 Apr 1993 14:25:54 GMT
Lines: 28

In article <1993Apr5.213803.10285@phx.mcd.mot.com> schuch@phx.mcd.mot.com (John Schuch) writes:
>In article <64@mlb.win.net> mbayern@mlb.win.net (Mark Bayern) writes:
>> 
>>>In article <1pdah8INNqdc@dns1.NMSU.Edu> mcole@scotty (COLE) writes:
>>>>I am having trouble driving a stepper motor.  I am driving each of the
>>> Could be that you're trying to drive them too FAST. I have found that many
>>Its the standard stepper resonance problem -- as was stated in
>>......
>>into position.  The rotor actually 'rings', and if you can plot
>>rotor position accurately enough you can see this. Resonance
>
>Actually, if you have an o-scope it's pretty easy to see the ringing.
>Just place a low-ohms resistor (one or two ohms) in series with one
>of the windings as a current shunt. place the scope across the resistor.
>Run the motor at a constant speed and adjust the timebase accordingly.
>The ringing is easier to see at lower speeds (around 10 steps/sec).
>The ringing generates back-emf which you can see on the scope.

It isn't quite that simple.  Most stepping motors have winding resistances
such that 1-2 ohms changes the drive characteristics noticeably.  Better
to use a 0.1 ohm precision shunt.  (Digi-Key sells these.  They are also
the thing to use to measure large DC currents.)

For what it is worth: Airpax has a nice booklet on stepping motors, which
they sent me free when I asked them nicely for info about one of their
motors.  It goes into quite a bit of detail, and includes several motor
data sheets.

