Your opinions on setting Vref

Hi all, I've never correctly set my Vref, but never had any problems on both of my printers.

I was wondering, what the general experiences are with setting Vref, for me it has always been setting the Vref by hand, just feeling and listening to what the motors do and how the machine behaves.
On the second machine I didn't even have to re-adjust anything, it all went right in one go.
I ask this because I see a lot of people getting confused with Vref and become scared to adjust tiny potmeters on stepper drivers.

Never had overheated motors, no overheated steppers either, and no problems with the motors hanging on certain prints or skipping steps etc. So I really doubt if it's effective.

The only time I did have problems was when I calibrated the Vref to the exact calculated value, because I use 2.5Amp motor, so the stepper drivers are not even made to output the full current. This was with the first printer I created.




Also, I'm not sure yet about the oscillator settings on the A4988, I have it somewhere halfway, I had the feeling the step/mm quality would not be as consistent when I had turned the potmeter all the way up.
Any thought on that?

Edited 1 time(s). Last edit at 01/08/2014 07:00AM by Ohmarinus.

On an A4988 it's usually easy to adjust them by feel, but with the DRV8825's, that rarely works.

The one thing that adjusting by Vref does do, is hopefully eliminate the stepper drivers as a source of issues when you're building the printer. Especially with some designs, it's easy to end up with issues caused by an axis binding in some/many places, which will still cause the motors to stall. If the Vref is set appropriately, then you're pushing the steppers to their max current/torque, so any issues are either:
- A bug in your assembly that is causing binding
- A bug in the design that is causing binding

Ah, so the reason would be to create as less of variables possible to mess-up the configuration. Sounds logical.

On my other printer I have imitation Pololu's and they also were quite easy to setup. I don't know if they are DRV8825's but I guess not, since I can't find out anything on the sellers website about that. Over there they are called Pololu Stepsticks, but I found out they are actually copies and not the original real deal.

I wonder, why would people not buy A4988's? I only see good things in them and they work very flexible and you can even set the oscillation which is a sure plus! And they cost the same

The DRV8825's can do a bit more current, and they support 1/32nd steps. The A4988's only support 1/16th steps.

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The DRV8825's can do a bit more current, and they support 1/32nd steps. The A4988's only support 1/16th steps.

Actually, i've thought about changing my pololus from 1/16 back to 1/8 steps. I guess that is still way too small to notice a difference, while on the other hand raising the microsteps gives a huge performance increase for the arduino.
Just a few numbers: atm, i've got 1/16 microstepping, that's in my case 100 steps per mm, so 1 (micro)step would be 0.01mm. That's incredibly small, i guess the cumulated backlash in the system is a lot more. Or do i have an error in my calculation?

Well, I don't know how it works for steps exactly, but my guess would be:

1.8º per step on your motor.

1/16th microstepping would mean

100 / 16 = 6.25%

(1.8º / 100) * 6.25 = 0.1125º per microstep

After this, it all comes down to the diameter ø of your gears, the thread on your leadscrews and the size of the belt-pulleys on your stepper motors.

To be honest, I have no idea how to calculate further haha

Edited 1 time(s). Last edit at 01/21/2014 07:30AM by Ohmarinus.