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[on:]

Hi all, I'm running two small 12v 0.4amp stepper motors off of my arduino uno and ladyada mshield. When I feed step commands to the motors, the initial position is inconsistent, but all subsequent commands are perfectly on target. The motors are not overheating and the other motors in my system are not experiencing the same problems, so I don't think my code is the issue. Has anybody experienced similar problems with small steppers?

I'm thinking that since the motors are only experiencing problems when they are first charged up, the problem could be worked around by telling the motors to begin drawing their holding torque current without actually telling the steppers to move. That way, they get charged up but the initial inconsistency problem is avoided since they aren't moving during that initial command. Is this possible to do with a stepper motor?

Any input/advice would be greatly appreciated!

[Reply #1 on:]

Also, I encounter this problem regardless of the motor's set speed.

[Reply #2 on:]

It sounds like the motors are starting when they are "off step". If the motor isn't on the same step as the microcontroller thinks it is, then it will jump a couple steps to get coordinated, then run as it should.

If you apply a holding torque (not sure how to do that with the library) it still may jump to get coordinated. All the holding torque does is hold on a step. If the motor isn't on the same step as the applied holding torque , it will jump.

A possible solution is either manually turn the motor to the step that the software starts on, or run it forward a certain number of steps, then backwards what ever number of steps required to get it to the correct starting point.

[Reply #3 on:]

So is it possible to use microstepping to increase the effective number of steps of the motor, so that the distance the motor 'jumps' to get back to position is relatively small? I'm not sure if this is a mechanical problem or a coding problem. The small steppers I'm using have only 48 steps per revolution.

[Reply #4 on:]

Think of it this way. The motor has 4 steps, and they go in this order ABCDABCDA... ect.
Suppose the motor is stopped on step D.

If the controller fires step A (the next one), the motor will go forward one step.

If the controller fires step C, the motor will go backward one step, then continue forward stepping

If the controller fires step B, the motor might jump back 2 steps, or it might jump forward 2 steps. Then it will continue stepping normally.

Using halfstepping won't solve this problem.