WIP ExoSlide based CoreXY Printer
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nice electronics box!
One comment though: three z leadscrews will be enough to carry the bed and allow you to use auto bed leveling. four will overconstrain your bed.
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@oliof Correct me if I'm wrong, but it looks like in this case the gantry is moving in Z and the bed is fixed, a la Voron?
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@whopping-pochard It certainly looks that way.
@oliof The bed itself looks to be stationary and mounted at 3 points. The gantry raises in Z. Which still leads to a motor synchronization and tramming problem.
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oh right. Still overconstrained though (-:
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Overconstrained and it would seem to me to be much more difficult to design enough compliance into the gantry to allow for proper adjustment anyway.
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Yes, the bed is fixed and the gantry is moved on 4 leadscrews. This was how it was designed, I hadn't thought about changing it or that it might introduce problems
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Is having 4 Z motors not a good idea? I thought I had seen it around a bit..
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Forgot to add a shot of the electronics box so far. I posted this elsewhere asking about cooling but figured I'd want one here in the build topic
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@cdthomas9 said in WIP ExoSlide based CoreXY Printer:
Is having 4 Z motors not a good idea? I thought I had seen it around a bit..
Oft used and oft maligned. 3 points define a plane, so 4 points adds an extra constraint. When dealing with the flat plane of the bed that just makes it difficult to get leveled since every adjustment changes the position of the other points and the end result is often a saddle shape. In your case though, the bed is fixed and the gantry is moving. This adds a lot of complexity to the system.
It's not impossible to get them all 4 points lined up, but it does require more compliance in the joints to allow for contorting the gantry to be in line with the plane of the bed, which adds complications because the XY motion system is relying on the gantry to be rigid.
Using 3 points for lifting the gantry probably isn't practical due to the need for rigidity and stability, so 4 points might be best.
So 4 points and you can't really build in flexibility to allow for adjustment, so you need to get everything lined up perfectly to prevent binding. It's not impossible, just difficult.
If you haven't already I would suggest studying the Voron2 which uses a XYZ gantry like this, but lifted at 4 points with belts on rails. I think they have built in some flex to the gantry and then have a routine to square it up.
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That's a pretty slick machine, the manual is extremely well done and the engineering looks pretty good. I'd rather have leadscrews over belts, I just feel better about having solid hardware holding the gantry up. Hopefully everything works out and if any issues come up as I progress through the build I'll be able to get them addressed. I may wind up rebuilding this thing at some point if the design gives me problems but we'll have to see. Thanks for your help so far!
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Good luck. I'll be interested to see how it works out.
