HadleyRille

Great idea putting it into the firmware! Seems to me that it would be pretty straightforward for standard linear moves (G0 and G1). Just look for a direction change between movement commands and insert a backlash takeup step there.

If you have an arc with a direction change in it, break it into two arcs with a backlash takeup move in the middle.

As you see from the video, the GRBLshield will work with a fairly large mill, but it really is pushing it. While those aren’t the largest motors that I could run with those driver chips, they’re close. They’re 1.7 amp motors from here:
http://www.phidgets.com/products.php?category=23&product_id=3308
As you see from the video, I’m trying to get extra torque by running at relatively high voltage (27V). If I were doing it again, I might go a little closer to the current limit with these:
http://www.phidgets.com/products.php?category=23&product_id=3307
I was worried about thermal load on the chips, but with the fans going it seems to work just fine.

I made all of the motor bracketry myself using the mill in manual mode. The x and y axes had tapped holes available that looked like they were meant for mounting a power feed, so I attached to those. Since I still wanted to use the handles, I machined extension shafts that bolted on to the pulleys and attached the handles to those.

The belts and pulleys are pretty standard 1/5″ pitch timing belts. I used to build a lot of motion control equipment and had a bunch lying around, but you can get them from Stock Drive Products:
https://sdp-si.com/eStore/

The power supply came from Jameco.com. The fans and switches came from recycling obsolete equipment, and the case I mounted it all in is an old hard drive enclosure.

The down side of all of this is that it can’t run very fast. The time lapse shots in the video of the mill cutting are sped up 20x. I suspect it would run a bit faster than that, but I was being a little conservative since I didn’t want to ruin a piece with a motor stall. To get it to run faster, I’d have to use bigger, torquier motors, but that would have bigger torquier drivers and much higher cost.

I’m looking forward to seeing Riley’s python control program. Gctrl works, but leaves a lot to be desired. I started writing one too, but it wasn’t done in time for my video and I’ve put it on hold now that i got all of those brackets finished. My program does some nice things like estimating total program execution time, and stripping out comments from the g-code (since comments make g-code much easier to read, but GRBL chokes on a g-code command that includes a comment). You’re welcome to have any of it (or my path plotting code ) if it is of any use.

There is a Processing sketch that I’ve been using. It’s available here:
https://github.com/damellis/gctrl

I made a little video about my workflow:

That should be enough. I tested mine with a similar supply. If the blue light is coming on and you’re able to send commands that get acknowledged with an “ok”, then the problem is in the motors or how they’re connected.

Are you sure you have the motor connected properly? With a two phase bipolar motor, you should connect one phase to the first two pins and the other to the next two. If you have one phase reversed, the motor might run rough or not turn at all, but you’ll definitely hear it trying.

It’s also possible the current adjustment pots are turned all the way down. If that were the case, you wouldn’t get any movement either. Issue a long movement command like “G0 X1000” and try turning up the current until the motor starts turning.

Finding the sweet spot for the current pots for my motors was the trickiest thing for my setup. I don’t have any good way to measure how much current was being delivered, and had to do it by trial and error.

Thank you. I should have my motors in a week or so and will report back.