Head can not move small distances

[iancaz]

Okay, this is likely something simple, but I'm a noob, so I'm hoping someone here can help me out!

I'm using OpenBuilds CONTROL software to run my Arduino UNO based table. I can successfully jog 10mm, or 100mm per jog, but if I take it down to 1mm, or .1mm, the table clicks & nothing moves. I have occasionally seen it "rock" in the direction I expect it to go, but then it falls back to where it just was.

I tried dropping acceleration down & it did provide some help (moved at 1mm per step), but it was so slow, there's no way I could use it that way to actually cut anything.

Does anyone have any ideas? I can provide additional hardware info if necessary, but not sure what is relevant.

Thanks,
Ian

[weldguy]

Hey Ian, I am not pro but it sounds like your stepper motors are not moving in fine enough steps to complete these short moves. Could be a gear reduction issue or a stepper driver setup issue but I am not sure, just throwing that out there.

[iancaz]

I'm wondering if I need to use (more) micro-stepping?
My stepper drivers minimum pulses/revolution setting is 400, but my stepper motors are 200 pulses/rev, so I'm already doing some micro-stepping. I'm wondering if increasing this would give me the increased resolution I'm looking for?

[weldguy]

Im not familiar with your equipment but it’s certainly worth a try. Likely just a flip of a couple dup switchs or something to make it happen. Good luck and let us know how it works out.

[adbuch]

I'm wondering if I need to use (more) micro-stepping?
My stepper drivers minimum pulses/revolution setting is 400, but my stepper motors are 200 pulses/rev, so I'm already doing some micro-stepping. I'm wondering if increasing this would give me the increased resolution I'm looking for?

Hi Ian,
I built a small cnc router/plasma cutter several years ago using an Arduino Uno R3 with GRBL control. As you most likely know, GRBL can be programed into the Arduino and converts G-Code to stepper motor xyz motion. GRBL has a list of programmable parameters for things like steps/rev, acceleration, turns ratio, etc. I am using Nema 23 stepper motors, and have the micro-stepping set to 16 with dip switches on the stepper motor drivers - which gives 3200 pulses/rev. of the stepper motor. Your 400 setting would translate to 800 pulses/rev. Depending on your turns ratio, 800 pulses/rev. may not be able to provide sufficient resolution for 1mm or 0.1mm increments of motion. You also want to make sure that you have matched the output/drive current of the stepper motor drive to the current rating of your motors. This is normally selectable with dip switches on the stepper motor drive.

I would need more information about your parameter settings and mechanical ratios to try to help you in more detail.
David

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[iancaz]

As it turns out, the biggest change (and immediate fix) was to change $1=255 (Step idle delay), to essentially shut it off, to keep my steppers from rolling back after a step.

The second suggestion, which is the same as yours, was to increase my micro-stepping to 16,000 steps/rev, or 1/8th micro-stepping. This gave me MUCH better resolution overall.

[adbuch]

Ian - glad to hear you've got it fixed. Maybe you could post some pictures of your project so we can see what you are working on.
David