stepper motor making weird noises...

So I've finally gotten my unipolar stepper working! Before it did not work too well, going in random direction, making
funny soundes etc...
So here is what I've observed and am still having problems with. Currently the only way I can get the motor to go a nice speed is to ramp it up from maybe 50Hz and then ramping it to a few kHz. However in the mid range frequency the motor starts to make weird nasty sounds! what could be the reason of this? also is there a reason why I have to ramp it slowly? I feel like I should be able to get this guy up and running pretty quickly, am I wrong? Help!!
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snipped-for-privacy@gmail.com wrote:

This sounds about right. Stepper motors always have to be ramped up and down in a controlled fashion, especially under load, else they will stall out or start missing missing steps. Motor torque drops off significantly as step-speed increases. Also, they have various resonance phenomena, which is what you are observing, and which need to be addressed based upon the specific situations. Some resonances are due to the motor alone, and others from the motor in combination with the load.
There is some good basic material regarding all of this here ... see fig 2.9, etc ...
http://www.cs.uiowa.edu/~jones/step/physics.html
You can get the thing up and running pretty quickly, but the ramping rates have to be specifically tuned for the motor and specific load.
- dan michaels www.oricomtech.com ======================
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"Going in random direction" Sound familiar. When I built my first step motor driver it worked great with some motors but not others. If you're not already, try both diodes reversed biased across the coils to eliminate the back EMF and diodes in line with the phase wires forward biased to protect the driver. I had similar problems and after adding the diodes it worked great with all step motors I tried after that. I was using a pic16f877 to control the step motors and interface to a computer through an RS232 port. Commands where sent to the controller using hyper terminal.
Hope this helps,
Dennis

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