Dual motor auto-squaring

[Zorki4]

Hi Schildkroet,
Can you add support for dual-motor axis?
The only difference is in homing procedure. Slave motor must have additional limit switch, then software can home two motors of one axis independently. I think it should be quite simple to add.
This option is included in grbl 1.1h.
Best Regards.

[Schildkroet]

Hello,
this feature is currently not planned, but i might add it later if i find some time for it.

[Zorki4]

Hi.
I'm not very good at programing and neved used ARM processors, but since grbl-advanced is based on orginal gnea/grbl i'm was able to make it work (just using copy-pase method, and a little bit of tuning to match new processor). Everything seems to work properly. I think that after a few days of testing i'll be able to share modified code.

I'm new to the github, and not shure how it works. Can I add modified version?

[Schildkroet]

Usually you make a Pull Request
Or you can send me the source to include the diff

[Zorki4]

I had to switch back to previous controller, because i had some problems.

There is something wrong with speed of the movement. Machine is decelerating to about zero feed between G-code commands. It is most visible when acceleration is set to low value (100mm/s, I normally run 750mm/s). Circle movement is best example: it is not one full circle, but four quater-circles, so machine slows down every 90 degree.
Same g-code on standard grbl runs OK.

I dont think i have changed anything in the section where speed (feed) is calculated.

Im was not able to create pull request on Schildkroet giihub. I had to make my own fork on my account, and there is pull request. All of the changes i've made are clearly visible there.

[Schildkroet]

This slow downs are known #30 and are caused by backlash compensation

[Zorki4]

That was it!
I still need few days to add some #ifdef to GPIO.h and GPIO.c, but i think that the rest is good enough and should work OK.

[J-Dunn]

Zori, did you ever submit a PR for this? It sounds like it could be useful.

[WolfgangBlack]

I'm building a cnc router and would love to have squaring for dual Y stepper and a rotary axis....

[J-Dunn]

I'm building a cnc router and would love to have squaring for dual Y stepper and a rotary axis....

I looked into this and decided a hardware solution was best. Some stepper motors are available with a spindle protruding both ends. You can then add a 10mm toothed belt and pulleys for minimal cost. You then adjust the relative position of the two ball-screws and lock it up permanently. This means the machine does not go out of true each time you power off or reset.

Check the lengths of belts available to avoid buying a custom length or adding a tensioning pulley.

[J-Dunn]

BTW , I think upstream GRBL now has dual motor zeroing , so this could be back ported to this fork.

[WolfgangBlack]

I am building a QueenBee Pro and would love to autosquare the Y axes and have a rotary axis A.
That would be my ideal setup for this CNC router.
I am using external drivers so would love to use the 4 on the CNC Shield v3.51 for X, Y, Z and pull signals from the Nucleo board to drive a rotary axis later on.
I am using 3d printed covers for the steppers to house 4 pin microphone connectors for the cabling and may have room at the from of the machines for pulleys and a belt to sync them but it is 1500mm apart so not sure how good that would be.

[J-Dunn]

With a belt that long you will need a means to adjust tension. Probably go for wider than 10mm. My axes are about 70cm apart. I Don't see much sense in the complexity of independently driving two Y motors for auto-squaring. This is something you want to set up once like setting your Z vertical. It does not make sense to redo that every time you power on.

[lairdgit]

J-Dunn,
I have a question about your machine spindle motor. Is it speed controlled with PWM?
Thanks, Laird

[WolfgangBlack]

Autosquaring is used by a lot of people on CNC machines for a few years now.
The MPCNC has dual X and Y motors and relies on it heavily.