Odd stepper performance on a brand new machine

Odd stepper performance on a brand new machine

Postby 4DThinker » Wed Feb 06, 2019 9:19 pm

We've got a brand new Probotix GX225 (formerly their Comet CNC) that has two Y motors to move the gantry.

The machine homes properly.
Any jog or g-code move in the +Y direction is fine.
All G-Code and jogging moves in the -Y direction start with an odd counterclockwise spin of the right Y stepper before it reverses to spin clockwise to bring the gantry toward the front. This leaves the right stepper behind the left stepper and the gantry racked.

Any clue what could be causing this initial counterclockwise spin of just the right Y stepper?

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Re: Odd stepper performance on a brand new machine

Postby martin54 » Sat Feb 09, 2019 7:05 pm

What's the machine home position? I would have expected to see the same thing happen when homing. does the machine home X & Y in a negative direction?
How is the y axis set up in the control software ? Is it set up with a slave for one of the Y axis motors & if it is which one is the slave & have you tried switching them over to see if the same thing happens ?
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Re: Odd stepper performance on a brand new machine

Postby 4DThinker » Sat Feb 09, 2019 9:42 pm

Homing sends the spindle to the left front corner. Y direction is front to back . X is left to right.

Despite the right Y stepper doing an odd reverse spin before spinning the correct correction, the homing routine waits for both Y limit switches to be hit before moving on. This squares the gantry each time the machine is homed. Any +Y move (jog or g-code command) proceeds correctly. All following moves with a -Y component make the Y2 stepper begin with a reverse spin before eventually spinning the correct way.

So I know something is wrong along the path from LinuxCNC through a parallel cable to the controller box. Both Y steppers should be getting exactly the same commands. The right Y stepper is getting (or just assuming) a +direction signal initially before then getting a correct -direction signal. Like any -Y signal after a +Y move gets there late. Sequential -Y commands proceed normally.

Probotix has sent a new controller with new parallel and usb cables. I'll know Monday if they correct the problem.

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Re: Odd stepper performance on a brand new machine

Postby 4DThinker » Tue Feb 12, 2019 2:51 am

It turns out that the mystery was a flaw in the initial parallel cable that came with the CNC. After swapping in the new cable that they sent the machine started working correctly as expected. More than a few times I've seen initial problems with new CNCs running LinuxCNC were due to defective parallel cables.

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Re: Odd stepper performance on a brand new machine

Postby martin54 » Wed Feb 13, 2019 11:13 pm

Thanks for updating the post, always good to see how things were fixed, read a few posts on various forums where cables ended up being the problem, not just parallel but usb & ethernet as well, various control software not all the same one.
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