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Stepper Driver Questions

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picclock:
Hi Chuck

hats an interesting stepper combination you have there. The driver board is a bipolar driver. This means that its for driving two coils which are isolated from the motor body. Bipolar motors are usually specified by their maximum current, although sometimes a breakdown voltage may be specified. Bipolar means that the current can flow either way in the windings which enables a fast changing magnetic field polarity.

Unipolar motors have center tapped winding(s) with the tap going to the supply. The motor is stepped by sequentially pulling the coli ends low, allowing a current to flow through them which creates the magnetic field. The problem with unipolar stepper motors is that there is no fast way to accelerate the magnetic decay. Additionally, as they are voltage driven, the current is limited by the winding resistance, which causes them to run much hotter for the same power.

If you increase the voltage on a bipolar stepper the current from the supply goes down and the current in the winding remains constant (or nearly so). On a unipolar motor the current increases pretty much in line with ohms law.

Not sure this post is helping you much. From a personal point of view, having used both types of stepper motor, I'd swap it out for a bipolar one and use a 12-24v supply.  Page 29 clearly shows the two bipolar motor windings on the right of the page.

Hope this helps a bit.

Best Regards

picclock
 


   

Chuck in E. TN:
picclock, The stepper I have is a uni. I have wired it up to the driver as bi-polar. Seems to work o.k.
Chuck

picclock:
Hi Chuck

I'm glad to see you dodged that bullet. It never occurred to me that you could do that, and I've never seen that done before. Presumably you can measure the resistance of the coil, work out the current at its rated voltage and set the driver accordingly. Once the current is set the driving voltage becomes relatively unimportant, so 12 - 30 V will likely make no difference, as the average voltage across the windings will be set by the current.

Is this to be direct drive to the worm gear of the RT ? I will be interested to see how it performs as I have a few unipolar motors in my junk box, which I've always thought of as junk which may have a new lease of life using this technique.

That's an Excellent solution  :bow:





Best Regards

picclock

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