Synced axis but 2nd motor at a different ratio than 1:1?

JRDM

I would like to sync a secondary motor to a primary motor, but have it run with fewer pulses by a ratio set in the configuration file. Is there a way to do this? If there is, I couldn’t figure it out.

Thank you.

dc42

There is no official way to configure that, because when multiple motor drivers are assigned to an axis, all drivers receive the same step pulses. But here are a couple of suggestions:

If the movement ratio you want is a fixed binary multiple, it's possibly to cheat the firmware and set different microstepping on the two drives.
You could use different size pulleys or gearing so that the motors need to move the same amount.
You could use a separate axis (e.g. U) for the extra motor. Then process the GCode to add the movement of the extra axis to each G1 command.

What is the application?

JRDM

@dc42 said in Synced axis but 2nd motor at a different ratio than 1:1?:

If the movement ratio you want is a fixed binary multiple, it's possibly to cheat the firmware and set different microstepping on the two drives.

You could use different size pulleys or gearing so that the motors need to move the same amount.

You could use a separate axis (e.g. U) for the extra motor. Then process the GCode to add the movement of the extra axis to each G1 command.

What is the application?

I've built a pellet-fed extruder that I'm getting close to firing up. Because of the head geometry above the feed throat, I'm concerned that the feed throat might not get a good material supply. I have designed a small cross-feed auger to make sure there's always material at the throat.

I was hoping for an easily adjustable ratio, but I can probably do a combination of 1 & 2. I don't think it needs to be a specific ratio, so I could probably fudge something close enough.

It's even possible this isn't really needed at all, but I would rather be prepared.

dc42

If it's for an extruder it's easy. Configure it as a 2-input mixing extruder, then adjust the mix ratio to get the speed ratio you want.

JRDM

I set up and tested the mixing g code and it seems to work fine so far. Thank you.