CoreXY belt configuration

[Brandon Pomeroy]

Hey all -- I haven't seen this particular belt configuration on CoreXY before, so I thought I'd post it here. I came up with this while trying to make a sane way to clamp CoreXY belts to a carriage, since having the belts offset in different planes is just ridiculous. Click the images to see a larger version.

This configuration makes the belts coplanar, and the belt clamp mechanism becomes nice and simple, just two flat plates pinching the belts to the carriage.

The idlers are made out of 4 F624ZZs, and the top and bottom spin independently of one another. Here's a view of the belt routing from the top.

Does anyone see any issues with this layout? I'm fairly sure the kinematics are still the same, but it's always good to get a fresh pair of eyes.

[whosawhatsis]

Two problems, off the top of my head:

First, your belt runs on the Y axis aren't straight, which means the length will change as they move. Watch how the cables go slack in this implementation to see why this is a bad idea: https://www.youtube.com/watch?v=50sjYI3Ftj0

Second, what you're trying to accomplish with the belt clamps can be done without the extra pulleys. See an example here: https://www.youtube.com/watch?v=RxQnnN1jjqQ

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[Brandon Pomeroy]

Thanks for the sanity checks - I noticed that my belts were changing lengths, but since it was only a ~1.5mm change, I discounted it.

To fix this, I just need to make sure that the belt paths coming off the motor pulleys are parallel, correct? I'll try changing to that YouTube vid's path.

[whosawhatsis]

Parallel to the direction of travel, yes. Only the parts runs that go to something moving need to be straight, the ones running between two fixed points can be at any angle.

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[Brandon Pomeroy]

Gotcha, that makes sense. I was able to fix it by adding in a couple extra pulleys. Belt length is now a stable 1065.79mm everywhere!