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big bite + pulley-configurations

A project log for 2.5-3D thing

a tiny-but-scalable three-ish axis-system *from* laser-cuts

eric-hertzEric Hertz 07/24/2015 at 10:070 Comments

I mighta bit off more than I could chew... was trying to get a functional-prototype done in ten days (first order free up to $20!), but my brain just stopped (or started?) working today...

Found yet some more design-flaws, even in reverting to that which was well-established (on paper)... the one that doesn't lend itself well to 3D... And those issues just started piling up to an insurmountable level, today.

The pulley-system I was planning to use for the third axis causes torquing on that axis... OK, fixed, now there's four more pulleys and two more cables... per axis (woot!)

Then... aww, I can't remember...

Oh, Tried to keep the openSCAD model easily-swappable between the two designs (3d-friendly vs. not) but now neither of them are working... MATH. Gave up on the 3d-friendly model for the "deadline", and still can't get the 2.5d model back to where it was... Wee!

On the plus-side, I did some cleaning today... the cat knocked over a box full of books, greeting-cards, and playing-cards... it's been quite a mess for weeks. And she's been using my books as scratching-posts! Also the rolling-table/workbench had a larger surface about two months ago... I replaced that surface with a smaller one, but never retightened the screws, much to my buddy's shin's chagrin. So, that's fixed, too, ish.

The "deadline" fast-approaches, and I still have to figure out how to convert the 3D model to 2D SVG for cutting, which is another huge mental hurdle at the moment. I know how to do individual parts, but this thing is a 3D model of *all* the parts, put-together... So, we're about halfway through till the "deadline" and at this point I'd already planned to start the 3D->2D process, and I don't have a full system yet to even attempt to do that with.

So, now, I have this crazy idea that if it's gonna be a snap-together "kit" of sorts, then why not have a bunch of pulley-locations available (holes already "drilled"), and make it a bit of a puzzle (kinda like the Cordwood Puzzel), like the puzzle that's going-on in my head the past few days (and 10+ years)...?

This "kit" could be supplied with instructions to build the model itself, but leave the pulley-locating as a challenge... 'cause that's how it's gonna be if I attempt to meet this "deadline" ;)

Anyways, I know the pulley-system *can* work; I've *done* it... and, if done-right, they actually add to structural-stability as well as smooth linear-motion/reduced torquing... But, can it be "done-right" in this new orientation/layout? Remains to be seen. Pulley-Mount-Holes Everywhere!

As far as pulley-layouts... there's a couple options... The *easy* one, requiring the fewest number of pulleys, makes each axis dependent on the others... e.g. if X moves 5mm, then the Y motor must move 5mm to compensate... This sucks as far as "glorified etch-a-sketchs" goes... but isn't hard to do in software... The "easy" one, requiring the fewest number of software-hacks (and being compatible with a "glorified etch-a-sketch") requires nearly double the pulleys. On the plus side, it means that each axis is completely independent of the others. This concept I dig. And it lends itself well to the "glorified etch-a-sketch" idea. Again, software-wise, it's completely unnecessary... how hard is it to say "Y=X+y"? But, again, LOTS more pulleys and cable routings.

And, frankly, the harder-software-hack version lends itself well toward testing the precision of multiple-axes WRT each other... which is something that could be worthy of attempting...

So... maybe... the solution is what I came up with earlier... lots of mounting-holes for various pulley-configurations.

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