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Topic: Another Stepper Motor Question (Full Revolution Exact, Precise Angles Not) (Read 2946 times) previous topic - next topic

blzalewski

I have a stepper motor driven by one of the new high current pololu drivers. It turns full revolution no problem (400 steps). However, if I tell it to turn 100 steps 4 times, it goes anywhere from 395-398 steps. Note: there's a disc attached to the top of the stepper motor so maybe the angular momentum has something to do with it but I'm still confused as to why it's working w/ 400 steps and not 4 x 100 steps.

Possible issues:

*Poor soldering? It's globby but shiny.
*I was unplugging the power supply and holding a transducer connected to a 400V square wave pulser and got a tiny shock.. however the driver is protected with a 100uF capacitor and the motor was not on

So what you guys think? Is the motor damaged or is the small disc (61.62 grams, circular, attached on middle) causing momentum problems?

I appreciate any feedback, thanks.

Erdin

You didn't mention what stepper motor you have (how much torque).
The weight of 62 grams is not a lot, but I can image that it could be a problem when you try to start immediately with a normal speed.

If you make the first step, you have to let the stepper motor start rotating, before making the next step.
That is why you have to slowly increase the speed, perhaps even using microstepping.

blzalewski

Thanks. The motor I'm using is 400 steps/rev 3V 1.7A/Phase w/ 48N*cm holding torque and 2.2N*cm Detent torque (http://dlnmh9ip6v2uc.cloudfront.net/datasheets/Robotics/42BYGHM809.PDF).

The way I'm trying to increase the speed is using an example from BreakoutJS --> I posted the technical details of it here: http://breakoutjs.com/topic/stepper-motor-configuration-w-driver-that-is-not-easydriver/. I'm trying to figure out how to modify the FirmataStepper program to work with a Pololu DRV8825.

I suppose I'll try microstepping: Is microstepping considered an alternative to using acceleration/deceleration profiles?


Erdin

Microstepping is not an alternative for acceleration/deceleration, it can be used for a better acceleration/deceleration.

Those stepper motor is only 3V, and the driver is minimal 8.2V
http://www.pololu.com/catalog/product/2132
http://www.pololu.com/catalog/product/2133
So they can't be used together as far as I can see.

blzalewski

what kind of driver should I be using for a 3V motor? also, what kind of stepper is supposed to be compatible with the pololu driver?

on the pololu website, they don't even sell any stepper motors that are rated above 8V. source: http://www.pololu.com/catalog/category/87

Erdin

I might be wrong. A stepper motor is more like a current thing. And some stepper motor driver can drive low voltage stepper motors without problems.
For example the EasyDriver can be uses for any voltage stepper, https://www.sparkfun.com/products/10267
So I don't know anymore what the pololu driver can drive.

But pololu says to use another driver for low voltage stepper motors, http://www.pololu.com/catalog/product/2134

blzalewski

I -think- the difference has to do with the supply voltage. The DRV8834 takes a power supply of 2.5V-10.8V.

From what I understand (this certainly should require verification before you apply it to your own project), a stepper motor can be run off a wide variety of voltages. The stepper's rated voltage is just the voltage used to rate the motor. For whatever reason, they chose to use 3V to generate their spec sheet. Using 3V will certainly be better for temperature considerations but 12V gives better torque because the rise time after the current is chopped is much faster. So I'm pretty sure the problem is not incompatible parts. I actually think it has something to do with the timings used in BreakoutJS (HIGHLY RECOMMEND to anyone who wants to integrate a web interface with Arduino --- put simply it's easier to use than MATLAB and LABVIEW).

Anyway, I'm trying to figure out the timings right now on this post: http://breakoutjs.com/topic/stepper-motor-configuration-w-driver-that-is-not-easydriver/ ---- maybe this "debug" will help someone else in the future.

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