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.