🚀 go-pugleaf

>In article <1992Aug14.214916.4173@colorado.edu> mathis@tigger.cs.Colorado.EDU (Don Mathis) writes:
>}I've got a 4-phase stepper motor that I'm trying to control, by
>}sending it the required sequence of 4-bit patterns (1001, 1010, 0110,
>}0101, repeat), and the motor runs for 2-6 seconds (hundreds of steps)
>}and then it gets confused and just starts wiggling.
>}
>}The motor behaves as it would behave if it had gotten out of
>}synchronization with the step commands, but I can't imagine why this
>}would suddenly happen after hundreds of successful steps.
>}
>}Can anyone give me some advice?

I've been invoved in doing detailed simulations of stepper
motor dynamics, recently, for a spacecraft antenna gimbal
project. We're simulating a device that will actually fly,
and so have put a lot of effort into finding ways to make it
fail (so that we can fix them). We've also gathered a lot of
stepper motor data from manufacturers. What you describe
sounds like one of two effects:
 
o If the torque applied to the stepper motor exceeds
  its rated torque, then it will lose synchronization.
  This can happen due to either externally applied torques
  such as friction, or due to inertial torques (i.e., you're
  trying to accelerate the load too quickly).
o Every stepper motor has an internal mechanical resonance
  frequency. This will depend on the amount of rotational
  inertia attached to the output shaft (the greater the
  inertia, the lower the frequency). When your step rate
  equals this frequency, slipping can happen, especially
  if the motor is experiencing a large torque at the time.

Hope this helps...
-- 

     Kieran A. Carroll @ U of Toronto Aerospace Institute
     uunet!attcan!utzoo!kcarroll kcarroll@zoo.toronto.edu