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Author Topic: Microstep issue?  (Read 882 times)
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I just about have my project done, but I'm a bit stumped on my stepper driver. I have a GeckoDrive G201X and am running it using AccelStepper. It works fine, but the G201X is 10 microstep and I don't think I can drive it fast enough for my project.

I bought a G901X which will let you run the G201X at Full, Half, 5, and 10 microstep. I haven't had a whole lot of time to play with it yet, but so far I've only been able to run at 5 or 10 microstep. Full or half won't turn the motor, but it will squeal until the code finishes running. I might be able to use 5 microstep, but I'd prefer full.

Any idea what would cause this?  I set the speed down in my code but it didn't seem to matter. Would a lack of current from the power supply cause full and half to fail, but let 5 and 10 work?

The reason I ask about current (and this is probably a dumb question), is that I have a DC boost converter as my power supply. It has adjustments for both voltage and current. Measuring voltage was obvious, but I am not totally sure on the current, so I just turned the adjustment a bunch. Is there a way I can test this? I assume it involves putting a multimeter (set to measure current) between the + on the boost converter and something that would put a load on the power supply? And I assume I'd want a load equal or greater than what my driver is set to use?



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I would throw out the boost converter and get a real power supply. Not knowing the rating on the boost converter, and how it limits current I would say this is the first place I would start. Second - How fast are you trying to run the motor? Are you using any acceleration? The faster you run a stepper motor, the less torque it has. SO - if you are trying to start the motion without any acceleration, the motor is not able to develop enough torque to overcome inertia.

#1 - get a real power supply with a high enough current rating and test it that way. A boost converter is not the way to go. The boost converter would need to have sever times the current rating of you motor/drive to function. That means even higher currents at your low voltage supply.

What voltages are you using? What motor RPM are you looking for?
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Thanks for the suggestion. I originally didn't use acceleration. I just tested it with acceleration and that seemed to fix the problem.

I'm not sure I have any alternative to the boost converter. I have to run this on a 12vdc electrical system and I need a minimum of 24v for the driver. I'm running the booster output at 36v right now, but may move that higher if need be. Here's a link to the booster I bought:
http://www.ebay.com/itm/DC-DC-600W-10-60V-to-12-80V-Boost-Converter-Step-up-Module-Power-Supply-/170893208817. I thought it would be enough to run one stepper. My stepper is a 425 oz-in and the specs are http://www.buildyourcnc.com/Documents/PN.SM60HT86-2008BF-U%20%28inhouse%20PN.60BYGH303-13%29%20%281%29.pdf. I have it wired in bipolar parallel.

Do you still think the boost converter I have is not the way to go? Is there an alternative that I can make work with my 12v system?

I think the faster the RPM the better. Maybe a bit over 1000rpm. I think I was at 120 rpm with the 10 microstepping, so full steps should be ok. I'm not as worried about being low on torque because I think the DC motor this is going to replace didn't have much of a torque rating.
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Boost convert should be fine - got enough amps (assuming it lives up to its description - cheap chinese PSUs aren't always
as good as they claim in my experience.

So measure the boost converters output voltage under load to make sure.

The keys to avoiding missed steps are not going too fast for the supply voltage and not accelerating
too fast for the hold-in torque rating.  36V I'd expect you to get to 500rpm OK, 1000rpm might be
pushing it.

Use the finest microstep setting you can - otherwise the vibration will reduce the motors ability to
hold torque.  Microstepping is all about smooth running, not so much about positional accuracy.
Physically damping torsional vibration can help hold lock - certain motor speeds will cause
resonance and these are when the noise is highest and risk of mis-stepping is greatest.   Up to a point
friction in the system can improve performance by damping resonance.

I'd set the converter to a higher output voltage - should get you faster max speed.

If the problem is the acceleration limit then tune the max acceleration down.
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Thanks for the explanation.
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1000 RPM is rather fast. As I stated earlier, the faster you go, the less torque you produce. It would appear that this is some sort of mobile application so you are trying to work with the power you have. For full steps you might look into a simple transistor based driver with less intelligence, though you might have to make provision for current limit when not moving to avid heating your motors. For that you might need a motor with a lower voltage rating, but 12V or lower rated steppers is not anything rare.

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Higher supply voltage will overcome this loss of torque at speed which is due to inductance in
the windings reducing the current at higher frequencies - double the supply voltage can
both double the speed at which current can change and overcome twice the back EMF.
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