Printed pulleys for reducing friction on the flexsors

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andreas
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Printed pulleys for reducing friction on the flexsors

Postby andreas » Tue Feb 24, 2015 5:50 am

While working on a Raptor Reloaded a couple months ago, I noticed that the friction on the flexsor lines was being evidenced by the wear marks on the cable routing channels on the palm. I think there are some not insignificant friction losses in these devices and wanted to propose printed pulleys as a potential solution to the problem. Files for testing on my github-- notice that the geometry is not a complete hand, but a small section of a palm to reduce print time and ease of testing.

pulleys0.jpg
Wear marks from friction on the flexsor lines.
pulleys0.jpg (79.06 KiB) Viewed 1506 times


pulleys1.jpg
Recess for a thumb pulley.
pulleys1.jpg (41.36 KiB) Viewed 1506 times


pulleys2.jpg
With thumb pulley installed.
pulleys2.jpg (70.31 KiB) Viewed 1506 times

The idea here is to make the pulleys tangent to the path of the line at the point where the line takes the biggest turn.

pulleys3.jpg
Index finger pulley shaft.
pulleys3.jpg (74.45 KiB) Viewed 1506 times

jonschull
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Re: Printed pulleys for reducing friction on the flexsors

Postby jonschull » Wed Feb 25, 2015 9:58 pm

This would be a perfect test case for a test measurement rig.

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laird
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Re: Printed pulleys for reducing friction on the flexsors

Postby laird » Tue Mar 03, 2015 6:53 pm

I think this is a brilliant idea!

I'm wondering if we could make this all out of 3d printing materials, by printing a bearing ring, concave on the outside, sliding around a piece of filament (which is strong and smooth)? It wouldn't be quite as low friction as a real bearing, but it'd be cheap and avoid needing special parts. Given that the tension lines don't move very far, a printed 'bearing' might work well, particularly if it's printed out of something slick like Nylon.

Perhaps a shape like:
pivot.png
pivot.png (40.4 KiB) Viewed 1469 times
- Laird Popkin

Peregrine Hawthorn
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Re: Printed pulleys for reducing friction on the flexsors

Postby Peregrine Hawthorn » Thu Mar 19, 2015 6:22 am

What about using a monofilament cable instead? The braided stuff can actually be used to saw through wood. This looks like it would add some excessive complications to the build process, and a simple change of material (one we already use) deals with this problem entirely.
Heavy duty hand user, and co-designer of the Talon.

I break hands and then tell you how I did it.


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