Ummm, yeah...so I'm just gonna upfront admit that this just plain didn't need to exist, and isn't even particularly successful...I mean, it holds paper towels, so I guess it's "successful"...anyway
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So the motivation here was that I got frustrated when I pulled a paper towel and got the whole roll, and but five minutes later, I pulled on the toilet paper roll only to be granted one square at a time. Clearly this wrong needed righting through improved dynamics, or somethin. I decided if I could crank up the damping (the velocity-dependent resistance), then the dispenser would basically pull back proportional to how hard I yank the paper, or at least that's the idea.
Key features/phrases to make it sound impressive:
- Base contains a magnetically-coupled fluid damper
- The base itself has an integrated stator and locating features/bearing races for the rotor
- The magnetic coupler between the rotor and the turntable also provides the preload for their respective bearings (and hold the thing together)
- The base is sealed with a printable TPU gasket
- Paper towel is 'secured' to the holder with the compliant, TPU post.
Soooo, I'm not really expecting anyone to do as I've done, and build one of these things, so I'm not currently planning to include a step-by-step build for this. But, if I'm somehow wrong, and you'd some more info, drop me a comment on Printables or the like...and I'll very much consider it :)
But here's a quick overview of the parts:
Base/Stator
The posts arranged around the middle are there to create additional drag in the working fluid and increase the damping. The grooves around the perimeter are for the gasket and adhesive to seal it up. And the cone cutout in the center is for a "jewel bearing" that locates the rotor and is...get this...a bearing :)
Rotor
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The bottom side of the rotor (image on the right) includes the mates for the above-referenced drag posts and jewel bearing. On the top, the five large cylindrical pockets are for the magnets that will do the coupling. And in the center and around the perimeter, more bearing races.
NOTE: on the bearing races on the top of the rotor, this is over-constrained, but I was worried about possible deformation in the rotor due to the magnets, and didn't want to risk the posts colliding. However, I think there is likely sufficient stiffness in the rotor to leave the inner race empty. So you'd only use the one jewel bearing on the bottom (with a single large ball) and the outer ring of 3/8" balls.
Gasket
The gasket is not intended as a stand alone seal, as the intent is/was to bond the shell together using a waterproof adhesive (like Goop...actually Goop, I used Goop). So the idea is to print the gasket from TPU, and lay beads of Goop in both of the flat regions. This has seemed to hold up great for mine. It's been about a year since I first built this and it hasn't lost a drop of oil.
Top Plate
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The bottom side of the top plate has the mates for the gasket and rotor bearings. As mentioned above, I would recommend only using the outer bearing race here. On the top surface are another jewel bearing cone and a v-groove race. Leave the cone empty, and only use the outer race with 3/8" balls.
Spool Plate
The Spool Plate could probably be printed combined with the Flexure Tube, but I separated them so that I could make the bearing races from a stiffer plastic like PLA. It has pockets for the other half of the coupler magnets, and a v-groove for the bearing on the bottom, and a recess for gluing on the Flexure Tube on top.
Flexure Tube (aka the actual paper towel holding part)
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Guess it's pretty much been covered already above, but it's a flexi part, intended to be printed in TPU, but i've also made them from PETG (but much less 'flexi', of course).