# 0.68 calibration failure and belt chewing

that makes sense, but why is there extra belt spooling out beyond what’s needed
to give minimal slack? when the belt is slack, why is the motor spooling any
more out? it’s not being pulled at that point, right?

David Lang

I have been thinking through this and it seems we should be able to get very close (at least in the horizontal position) with only two points.

If we start with the two belts on the diagonal and tighten them and make the two belt lengths even, then connect the other two and tighten, we will have four known lengths.

If we then move a known distance down one diagonal (say half way), you are letting our and taking up the exact amount on two motors and letting the other two just spool out under the movements control. Once stopped, tighten the two which were spooling and take note of the length.

We now have enough information to calculate two of the angles and from there we can determine the lengths of the four sides.

I know this is all theoretical and does not take into account the physical factors, but the math works.

I also know this would be a problem in the vertical position as gravity will make it hard to get a straight line on the diagonal.

Could this get a close enough to then do a calibration with the belts properly spooling on all four sides?

EDIT: On thinking more, this works if all 4 corners are 90 degrees. Likely need to do the same move to other side of center and do math to account for out of square corners.

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Mine are certainly not aligned, and in fact my top-left right now is temporarily negative of the bottom left. (I moved it way down on the side of the frame to try some more calibrations and not have to climb up a ladder 12’ off the ground.

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That is what I expected. That is why we need the 3rd point. Two points will not do but 3 should.

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@bar Is there a link I’ve we want to buy a second set of belts? If you only plan on using 1 size frame… Do you think cut off some of the excess belt is a bad idea? Any idea of when the new calibration video or guide will be out?
Jeremy

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We’re working on getting them up in the store ASAP. We have plenty of extra belts, but we want to sell them with the spools because they are glued together so we’re waiting on more spools. They’ll be \$5-6 per pair.

I’m not sure about the video, I want to see if my new plan for improving calibration works first so the video isn’t out of date immediately, but we have the group build day this weekend so I probably won’t be able to work on it until Monday.

Whats the best way to replace the belts? ive got some replacements arriving this week and finding it difficult to remove from the spool due to the glue.

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Thats why @bar wants to sell the spool and belt together - once glued together they may not seperate cleanly and so both should be replaced together.

I have to replace a belt this weekend too. I’ll probsbly try acetone to see if it loosens the superglue without damaging the plastic spool but have the replacement spool, too, if it does.

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Well, another one bites the dust. @bar Do you know when the replacement spools/belts will be up on the shop?

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They’re supposed to ship from the factory Wednesday so hopefully this week!

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Do not forget to run your stepper motors all the way up to free the router and arm unit from the base before you start disconnecting things. Also I have 2 screws that appear to be stripped (One in the belt end and the other in the V clamp thingy) but bed time is not when we try and drill things out. So I’m going to start a new belt guide printing and go to bed

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Replacement belts arrived and Maslow has all his arms back.

Installed 0.69.2 and the calibration process went much more smoothly. No excess belt , and it finished with a fitness of 0.5403331694322719. (Log attached)

Jogging around feels nice so im going to try a cut… wish me luck

m4 log.rtf (43.7 KB)

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Success!

Quickly sketched a 100mm circle, square, and heart in Sketchup and used kiri:moto for the CAM.

Only doing a 0.5mm DOC as I wasn’t sure on speeds and feeds yet. Bed time now but tomorrow I’ll start cutting some full sheets for a project thats been waiting for Maslow.

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