Gearhead vs direct stepper belt drive for smoothing out axis
30 Sep 2017 22:11 #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?
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?
Please Log in or Create an account to join the conversation.
30 Sep 2017 23:40 - 30 Sep 2017 23:40 #99707
by rodw
Replied by rodw on topic Gearhead vs direct stepper belt drive for smoothing out axis
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.
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.
Last edit: 30 Sep 2017 23:40 by rodw.
Please Log in or Create an account to join the conversation.
01 Oct 2017 01:02 #99709
by blazini36
Replied by blazini36 on topic Gearhead vs direct stepper belt drive for smoothing out axis
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.
Please Log in or Create an account to join the conversation.
01 Oct 2017 04:24 #99720
by rodw
Replied by rodw on topic Gearhead vs direct stepper belt drive for smoothing out axis
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
Please Log in or Create an account to join the conversation.
01 Oct 2017 08:31 #99727
by Clive S
Replied by Clive S on topic Gearhead vs direct stepper belt drive for smoothing out axis
You have not stated the voltage and current that you are using to drive the stepper?
Please Log in or Create an account to join the conversation.
01 Oct 2017 12:14 #99730
by blazini36
Replied by blazini36 on topic Gearhead vs direct stepper belt drive for smoothing out axis
Running it at 24v and 2a. It's rated for 2.8v and 2a
Please Log in or Create an account to join the conversation.
Time to create page: 0.232 seconds