Gearhead vs direct stepper belt drive for smoothing out axis

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9 years 1 month ago #99701 by blazini36
I'm working on a machine that currently uses a GT2 belt and 20t pulley on a nema 17 stepper and a microstep driver set at 4x. I intend to change to a 3M belt soon. It's using 16mm round linear rails and bearings. Initially setting this thing up I was not worried about movements in relation to actual measurements, it just had to move to the same spot it was set to in software. I used step scale to smooth it out

Now I'm at a point where I need to add things to the software that relate to real world dimensions. Assuming my math is correct I wind up with a step_scale of 508 to relate to 1 inch of movement. Even though the axis is smooth and easy to slide without the motor it has a jerky motion to it when driven by the stepper , it only runs at 2-4 . I'm assuming this is because of the low step rate. Direct drive a 4x microstepping has plenty of torque and holding torque. Raising the microstepping and scale makes it pretty weak. So I'm thinking I need to use a geared stepper which should require a higher step rate and I assume smooth it out. With a 3mm belt pitch and 5:1 gearbox @ 4x I'm calculating 1693.33 steps/inch. which sounds a little better.

Does this seem like a good idea?

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9 years 1 month ago #99707 by rodw
Very definitely.

See what was said about my direct drive here that made me rework it.
forum.linuxcnc.org/30-cnc-machines/31509...n-drive?limitstart=0

I think the belt reduction is the way to go. a zero backlash gearbox becomes very expensive. Most cheap gearboxes have a lot of backlash.

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9 years 1 month ago #99709 by blazini36
Took a quick look, looks like a very nice machine. Right now the 2mm belt/20t pulley is 40mm/rev on the stepper. I have a 16t pulley but I don't like the idea of a pulley that small, I also don't really like the gt2 belt but they are readily available and allowed me to get started. A 20t pulley on a 3M belt puts me at 60mm per rev if it were direct drive but the 5:1 gearhead obviously requires the stepper to run 5 revs to reach 1 rev of the output shaft. Common geared steppers are about 1deg backlash which is fine, this is not a machine tool I'm building. Missed steps would be a bigger issue.

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9 years 4 weeks ago #99720 by rodw
Thanks. I'm no expert but I think 40mm/rev is still quite high so a 2:1 or 3:1 reduction is going to make it much better. IF you follow my example, it should still bolt on as if it was a Nema 17 motor

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9 years 4 weeks ago #99727 by Clive S
You have not stated the voltage and current that you are using to drive the stepper?

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9 years 4 weeks ago #99730 by blazini36
Running it at 24v and 2a. It's rated for 2.8v and 2a

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