Caxis.comp was originally written by Andy Pugh to control a
single motor for velocity and positioning mode (spindle & c-axis). I don't think it was intended to control two separate motors.
It's not part of the mainline LCNC components, nor are there many people using it... so I don't think you're going to find a wealth of info on implementation. For your situation, there may be better approaches to managing your dual-motor arrangement.
The main hurdle to overcome for any spindle/axis (dual or single motor) is how to manage the axis encoder. Once you switch from axis to velocity mode the axis will generate a following error when LCNC sees the 'axis' encoder moving away from the commanded position. So we have to 'trick' LCNC and adjust the encoder value somehow.
- caxis.comp does this by intercepting the encoder output, and then subtracting the encoder change from the encoder starting value before sending that to the axis PID feedback input.
- Another method is to disconnect the encoder output from the axis feedback in spindle mode
The problem with #2 above is that when the encoder is re-connected (switch to axis mode) there is a significant following error instantly present. The switching scheme @Aciera came up with a while back for his lathe (using a single motor) looks like this:
- Step 0
- LCNC starts up with main spindle motor disabled
- Home C-axis before any spindle moves (at start of LCNC session).
- Step 1
- Command C-axis to C0
- Disconnect spindle encoder
- Enable spindle mode
- in Aciera's case that means switching his drive from position to velocity mode
- for a two-motor arrangement that means retracting the axis motor and enabling the main spindle motor via M-codes & digital inputs/outputs
- Step 2 - Run spindle as a spindle
- Step 3
- Use orient.comp to orient the spindle to 0
- Disable the spindle motor
- Enable the axis motor
- Reconnect the spindle encoder
If everything is adjusted properly (orient offset, C0 actual position, etc.) there should be a very small difference between Orient-0 and Caxis-0, resulting in (hopefully) a small twitch of the spindle at most.
For the past year I've been fiddling with caxis.comp and have recently come to the conclusion that it isn't going to work for me. There are a couple of annoying things I don't like (
can't disconnect the spindle easily to manually rotate the chuck), but the serious problem I found was that spindle synchronized motion wasn't working properly.
Something - and I'm not smart enough to figure out exactly what it was - in the caxis.comp scheme was causing erratic behavior (big motion jumps) during tapping and threading commands. Once I removed caxis.comp and use the spindle as just a spindle the tapping/threading stuff started working as expected. So now I'm re-doing a bunch of stuff in my config and will eventually wind up with something very similar to Aciera's arrangement.
So to sum up, I'd suggest abandoing caxis.comp for your dual-motor lathe and search for Aciera's config. I know he posted his files in the past year or so, although I think he's been working on a glitch with the encoder disconnect function recently.
