GRBL_ESP32 axes skewed, CoreXY movement, Bart Dring 2209 laser/pen controller

Not sure how hardware specific this is, or of it’s GRBL, or what.

I’m using one of Bart Dring’s 2209 laser/pen controllers, and have it configured for CoreXY movement.

When Lightburn connects to the serial port, it seems to do something to try to initialize the board. Sometimes, the axes end up getting skewed. X skews (what appears to be) 22.5 degrees towards +Y, and Y skews the same towards +X, so the axes meet at 45 degrees.

I have only observed this happening when LightBurn connects to the controller, not at any other time when doing movement testing. The device is configured as plain GRBL connected via serial/USB.

If I had to guess, I’d say that one motor is moving at half (Or maybe double?) speed, but obeying correct direction. Returning to the origin goes back to where it should.

I didn’t see anything weird in the results from $$ or from $S, at least nothing that I could identify as being wrong. motor steps/mm for the 2209 drivers look right.

once like that, I can correct the problem by powering down the controller, and then bringing it back up. It sometimes happens when I disconnect and re-connect the controller, and sometimes doesn’t. When it happens, it’s always after going to the “devices” button and reconnecting, but just doing that isn’t assured to cause it.

I don’t know GRBL well enough to really know what configuration could cause this, and I don’t know what initialization code LightBurn is sending when it connects.

… Help?

Well, given tht no answer is forthcoming, and that it only happens when I allow LightBurn to connect to the controller via USB, my solution will be to no longer allow LightBurn to connect to the controller via USB.