Microstepping not constant

Hi,

I´ve build a pan/tilt-head for a DSLR.

There is only a reduction by the pulleys of 1:4,5 on both axis. And there is no high load, which needs to be moved.

I'am using the DRV8825 stepper drivers and 1209-steppers from Pololu. (http://www.pololu.com/product/1209)
The drivers are controled by a Arduino MEGA. For the tests, I have just put the step-output in an slow ON-OFF-Loop.

Since I need a higher resolution, I want to use at least 1/8-steps.

After setting up everything and running couple tests, I have noticed, that the steps are not running constantly.

In the videos, you can see the unconstant movements. Trying different adjustments of the regulator on the DRV8825, did not improve the behaviour. To get fairly aceptable results, I have to set the regulator so high, that the stepper and the driver are getting hot (which is bad, because it is a portable setup, so I have limited battery-capacity and I don´t want to lose energy by heating up the components.)

I´ve also tested other steppers (0.9° and a little bigger). Same here, it is not possible to get equaly spaced steps.

The cable is about 1,5m long.

What could cause those unequal microsteppings? Would a special stepper or different drivers help?

I think steppers are not really efficient motors so i doubt its the type to run from a battery, but on the other hand i suppose you do not have much choice. For a mod, if you run it only full step (no microstep), its likely to get just a little better efficiency than in microstep mode. And if ran in full step, better go with 0.9 angle motors and try get some resolution increase with bigger gear ratio instead. Well, anyway this is just an opinion.

Steppers do run kind of hot in the usual manner. Hard to say which kind of hot is too hot. If you can keep your finger on it, that should be normal-ish.

About not equal steps i dont see a video in your post but here try check this out perhaps its informative.

If you try the driver with a3977 also mentioned in that post, that driver might provide more tweaks and hence my accommodate your motor(s) better. You could find it on reprap page as "stepper driver v3.3". But i dont think they are making this chip in plcc anymore, maybe you find some on stock or perhaps better as a3979 in plcc which is pin compatible and 16x instead of 8x. Good luck.

Nophead investigated uneven microstepping: [hydraraptor.blogspot.de]

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Generation 7 Electronics	Teacup Firmware	RepRap DIY

Thank you guys for the link. I have applied the mod and made some videos.

All tests were made with 1/8-microstepping and the same program on the Arduino, I just swaped the drivers.

Here is the Arduino-Code:

digitalWrite(24,HIGH);
digitalWrite(24,low);
delay(400);

This is the DRV8825 set to Vref=0,5V (=1A):
[www.youtube.com]

After applying this mod, it got better (still @ Vref=0,5V):
[reprap.harleystudio.co.za]

[www.youtube.com]

Using the Pololu A4988 with this mod(Vref=0,4V):
[hydraraptor.blogspot.de]

[www.youtube.com]


Setting Vref to 0,64V with the unmodified DRV8825:
[www.youtube.com]
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I can only get good results with setting the driver in FAST decay mode, otherwise it is not possible to get evenly steps in microstepping-mode. It´s still not 100% perfect, but much better then running the driver unmodified.

After modifying the drivers, I noticed, that the sound of the steppers got higher, which is some kind of annoying.

It is a pan/tilt-head, so I will just make 1-2 steps, pause some seconds, make 1-2 steps etc. To get a good and smooth video, it is absolutely necessary to have steps which make the same distance, otherwise you will see stutters in the video.

Are there some other methods I could try to get even better microstepping-results?

If you are getting noise from your steppers try upping your PS voltage. The switching frequency is dependent on the voltage so 24V should bring the frequency outside of hearing range. This has made a huge improvement on my printers.

I wonder how much this is affecting our prints as well. Every little movement affects how a print turns out.

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WWW.ZATOPA.COM - Your Place for high quality 3D Printing Filament and accessories

@jzatopa: I'am not using my steppers for printers. I´ve build a pan/tilt-head, which can move my camera. Going to 24V is not possible, since it is a portable setup which runs on 12V-batteries.


I was able to generate following graphs, which show you the moved distance of each step:

NEMA 14 stepper from Pololu at full-steps (constant steps, as it is necessary for my application):


NEMA 14 stepper from Pololu at 1/8-steps:



NEMA 17 from Trinamic which is descripted as "optimised for microstepping" at 1/8-steps: