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triangulation-free winch for Z actuation

Posted by realthor 
triangulation-free winch for Z actuation
May 11, 2015 03:12AM
Hi guys, I am pretty new to reprap forums so bear with me. I've been posting for a while (and still do) on Nic Seward's ConceptForge about a Wally without the radial or linear Z and without a threaded rod or leadscrew. I know little is left but in many parts of the world these parts are difficult to find and there are other reasons as well. Over several posts I've come to an idea of a winch that would spool Spectra Line while lifting or descending the SCARA arm on the Z axis. You can read the why's and how's over in Ideas for the Next Wally thread.

The problem with winches is that they have triangulation errors that don't count for a normal winching job, but for this particular situation any triangulation would mean a cvasi-impredictible Z resolution as the spooled line drifts away from the vertical, creating an angle. This could potentially be calibrated in software with some trig functions but as long as I don't know how to modify the software, I tried to think of a mechanical solution.

As long as we are 3D printing stuff, a solution I came up with is a spur gear bar with a threaded profile embedded (or a threaded bolt with spur gear teeth cut along its axis), so that the whole thing can be rotated by a wormgear while also advancing through some nuts. All this complication is for the spectra line to remain fixed on the bolt's axis and on the verical (to the anchoring point), while the line is spooled on the threads as it would on a drum.

To better exemplify i will attach a printscreen I have also posted on ConceptForge, but here I hope more people could pitch-in if interested, over there I mostly pester Nicholas, and I know he has a busy life.
Nicholas said he would be interested in prototyping it and I couldn't be more hapier as I have no real maker's experience (CAD or other engineering exp for that matter; I am also very new to 3d Printing). I can barely conceptualize things.

I've taken the stepper motor away of its position so that the spooled line can be better seen. I have the spooled line at the back, while the wormgear is at the fron, to prevent interfeering with it. Nic posted a CAD render with the wormgear at an angle with the bolt so that the contact is optimal. THis could clear up some space at the back so that a position of the stepper with the wormgear pointing to the wall could be possible.

Until Nic gets some time for this I would be interested in getting some feedback on possible issues that this approach would have and what could be some potential solutions given the constrains of the design.

Thank you.

Edited 2 time(s). Last edit at 05/11/2015 03:18AM by realthor.
open | download - screenshot.202.png (90.8 KB)
Re: triangulation-free winch for Z actuation
July 30, 2015 05:51PM
It is late here and I might not thinking too straight at the moment, but would it not be possible to keep a thread at a constant length between a point and a spool by compensating the difference in length with something like this [www.thingiverse.com]? Or maybe two of them on by the spool and the other at halfway.

Cheers and good night.
Re: triangulation-free winch for Z actuation
July 30, 2015 07:26PM
The point of the design is to avoid linear rods. Didn't have time to build my CAD skills to calculate and design a working prototype yet.
Below is a quick sketch, nothing properly calculated:

Have a good night smiling smiley, it's pretty late here too.

Edited 1 time(s). Last edit at 07/30/2015 07:32PM by realthor.

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