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Setting up step conf when using a gearbox

14 Feb 2019 17:30 #126474 by MONKEY0683
Hi I am new to this whole system. After spending over a year building a cnc router and working through some little niggles I have come across a problem that I would like some help with.

I am using 425oz-in nema 23 stepper's
Running a 10-1 planetary gearbox that is then connected to a 36tooth 5mm pitch drive pulley and belt.

I have set my step config as
8th microstepping
10-1 pulley
180mm per rev.

The problem is that when I try and test the axis the motors don't move. If I then lower my distance per rev to.0.18 mm I can get the pulley to move but I don't get a full rotation.

I'm sure this is all old hat and has been all discussed and sorted before but I generally don't have enough time to keep looking.

Any help or live walk through would be seriously appreciated.

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14 Feb 2019 20:33 #126491 by Todd Zuercher
First I think you have probably entered your gear box ratio backwards in Stepconfig.
Your scale that should be entered in your ini file should be 88.89steps/mm.

If you are not getting movement check that:
1. The drive is enabled and powered (motor is locked and you can't turn it by hand.)
2. Do a sanity check of your max acceleration and max velocity, this is specified in units/second in the ini file (mm/sec for a mm config.)
3. Check your drives minimum step and step space timings, and make sure you have set those settings in Stepconfig to at least 130-200% of those specified by your drive's documentation. Remember these numbers in Linuxcnc are specified in nano seconds. If your drive's docs specifies these in microseconds, be sure to adjust them appropriately (x1000).
4. Double check your drive wiring.

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15 Feb 2019 10:25 #126529 by MONKEY0683
hi Todd, thanks for the reply.
i dont beleive that the wiring or the power to the motor is the issue as i did have the table fully operational before.
I noticed that i was loosing position mainly on my Y-axis so i decided to change the layout.
One of the route causes was i was using tb6600 stepper drivers and they had started to fail. Also i found that unlike the X and Z axis i had very little holding torque on the Y.
The upgrades consisted of a new 48v power supply 2 new cw5045 stepper drivers and the 10-1 planetary gearbox.
i have added the steps from my step config to see if this helps in what im asking.
also how did you get the figure 88.89spm??

again many thanks for any help..

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15 Feb 2019 13:32 #126538 by Todd Zuercher
To get the 88.888889 I first did the math on paper, but I also double checked by putting the numbers into Stepconfig and got the same results. I've always found the input fields used in Stepconfig a little less than intuitive especially if you are not using a screw driven system. To get those numbers in Stepconfig I put in:
200 Steps/motor rev
8x Microstepping
1:10 reduction
180 Screw Pitch

The really confusing entry boxes are the ones for the "Pulley Teeth(Motor:Leadscrew)". In trying to dumb it down the authors made it confusing. It is the inverse of the gear ratio motor turns:screw turns. If you think about it as a toothed belt drive it makes sense. Since Stepconfig is asking for the number of "teeth" and not the reduction ratio. If you had a 10 tooth motor sprocket driving a 100 tooth one on the screw (10:100 or 1:10), That would be the same as your 10:1 motor to output gear reduction box.
The following user(s) said Thank You: MONKEY0683

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15 Feb 2019 13:34 #126539 by MONKEY0683
Thanks a lot. I will input these and go from there.

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15 Feb 2019 13:52 #126541 by Todd Zuercher
If the system was working and then developed missed steps. One of the 1st places to check are your drive to motor connections. It is not at all unusual for step-motors to have problems with burning out contacts in wire plugs or splices. And cable chain wiring can fail quickly if not rated for continual flexing. Also check for mechanical binding on your axis, such as a failing bearing or racking. The drive can also be suspect, and a replacement TB6600 is very cheap.

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