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#21 [url]

Mar 11 16 5:25 PM

This week I’ve been on Work Experience at Open Bionics, and I’ve been working on the fingernails.My first few ideas were to try tying different knots, using a loop attachment on the motor in the main body of the hand and tying an easily-adjustable knot (such as a Zeppelin bend or another such knot) but this didn’t help with assembly, seeing as one still had to pull out an incredibly awkward knot and retie it with no accurate measure of tightness. In addition, the knots chosen were all just too complex to be effectively tied with the tiny string (and even harder to tuck away anywhere).Then, I tried using a system of notches on the inside of the nail, allowing the loop of string (tied with a more simple knot) to be adjusted by small increments. The issue here was with the size the printer printed in: the notches, even with an extended fingernail, were just too small to show up effectively and be used. The only working design had two notches (which meant three settings total). This, of course, is both too crude and too imprecise to be used in the hand effectively and easily.After playing around with the ‘loop part’ (which appears a bit like the screenshot below, minus the crude fingernail attachment) I discovered that looping string through it in a certain way allowed said string to be tightened and adjusted without budging once the tightening was done (will provide photos when possible). This worked well on a scaled-up model, but the fingernail-sized one was a) still too big for the finger and b) really, really fiddly (not as much as a knot, but it was murder on the fingernails and very difficult to loosen due to its size).


After this I tried a few more designs, utilising notches in which to tuck string after feeding it through similar systems of loops, although none of these proved effective and again, the printer's resolution was lower than would have been liked.


In all, I made a decent amount of progress, but none of my ideas were refined enough to actually make the cut. Images of the prototypes will arrive in this or a following post. Said post will also likely elaborate further on the design process.


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#22 [url]

Mar 14 16 11:57 PM

Here is an idea for a tensioner, I think it is similar to what @TThomas was talking about.  I am not sure how practical it would be to print small and strong as I havent tried yet. Obviously it would require  appropriate cutouts in the fingers. If one end protruded out of the finger slightly it may be possible to attach a finger nail..

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#23 [url]

Mar 15 16 9:21 AM


It's funny you've just posted this. This is incredibly similar to the design we were discussing yesterday.

How is this part positioned within the finger? (what orientation) And what's the method for tightening it?
It seems that if both of us have come up with a similar solution, we must be on the right track.


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#24 [url]

Mar 15 16 1:30 PM

@OMac I think it would go vertically and would push into a star shaped slot near the finger tips, either in the fingers directly or in an ABS insert (if the ninjaflex deforms too much and allows the part to rotate). To adjust it you would pull it out of the finger tip and wrap the sharkline before pushing it back in. This would mean there would be a slight loss of tension due to the slack added putting it back in, so it probably needs to be quite squat to minimize that effect. 

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#25 [url]

Mar 15 16 1:49 PM

Thinking more, you could have it horizontally if you also had a fingernail part that screwed down over the top. That would reduce the slack issue as you wouldnt need to move it so far to adjust it. You could even have it so you screw down from the fingernail, through the finger and into a retainer in a silicone finger tip which might bring together a few different sub projects.

EDIT: it would necessarily reduce the contact area between the tensioner and finger/finger nail which may make it more prone to damage or slippage. 

Last Edited By: jaundice Mar 16 16 12:15 PM. Edited 1 time.

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#26 [url]

Jun 1 17 2:45 PM


I see this is a bit of an old topic but what is the resolution and range of adjustment that is required? Also, what is the tendon travel distance?


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