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Post from DIY Prosthetics

DIY Prosthetics | Projects | Claw Hand | Portfolio

  • One of our task was to redesign the fingers. We liked the original finger shape more or less, but not the dimensions. We wanted the the thumb to have a different thickness than the other fingers so that it could pick up smaller objects.

    We had many struggles with this design because we wanted the fingers to do more precision work, but also wanted to give someone the ability to still toss a ball around with their friends.

    Our first problem that we ran into was interference. We did not give enough leeway to the fingers to connect to the knuckles. We also had another problem with the fingers because the connector pieces and the actual fingers holes that the pin would go through did not line up.

    Because we wanted two different sized fingers, we had to create a whole other finger from scratch. We had a big problem with the measurements. We wanted to have precision movements, so the thumb and the index finger had to touch, which they didn’t. We had to extend the platform in which the thumb was on a certain distance so that they would touch.

    I learned to always model around pieces as to not mess up any measurements and to think methodically about which pieces to create first so that you did not have to work twice as hard to get the next piece done.

    We had also found another problem with the original design of the RoboHand. We did not like how on all of struts there were two, and you had to put like ten pins on each side just to have that piece be pretty flimsy. So Nathaniel and I thought, why not just make it all one piece. The problem in our design for the knuckles though was that the knuckles were slanted, so when we printed the first prototype of the struts, it did not align right. We had to go back into Rhino and go and edit the struts to make one of the pieces longer.

    Another problem we had was the connector piece to the knuckles. This piece was not hard, but I just was not thinking when made it. I made this piece after the finger, which was the wrong choice, because the piece did not give the finger maximum angle to rotate. Also there was interference with the knuckles, and it gave it almost no angle to rotate. Eventually I made the right decision and modeled the connector piece around the knuckles and the fingers.

    The RoboHand seemed like a very rough design and was difficult to get working and adjusted the way we wanted it. Main problems that we found were that the original design was difficult to string up and adjust, it could really only grab larger objects, and it was a bit rickety. To solve these problems, we basically re-designed the entire hand.

    Starting off with stringing it up, we did away with having to tie knots on the body of the hand. It was basically impossible to string up each finger perfectly. Some of them might have less range of motion, and others would bend all the way. Instead, we took ideas from the Violin. In order to tune a violin, you take out a rod, twist it to your desired setting, and ram it back in. It stays in the hole because the tunnel is tapered as well as the rod. We implemented this idea into our hand and now it is much easier to string it up and make fine adjustments to the fingers. It also looks extremely cool.

    The knuckles also got a make-over. The original RoboHand had a straight knuckle and didn't allow for a wide array of movement. By angling it, much like a human hand, we could have a wider range of movement and possibly more grip. Unfortunately, this meant that we would have to change the side bars so the entire hand could rotate and still have parallel side bars. We also changed the position of the thumb to under the index finger which would make it more like a claw. This would make it easier to grab small objects. At first, we made a lot of mistakes. Our 3D models weren't closed polysurfaces, which became a huge waste of time and was extremely frustrating. But after making sure all of our objects were correct, we were finally able to print.

    Sadly, after printing out all of our pieces, and finally getting the chance to put it all together, we realized how many mistakes we really made. The pieces all had too tight of tolerances and would either not fit together, or have a lot of friction and not move freely. The only thing that really worked was our solution to stringing it up. It, for the most part, worked perfectly and would be a great design change for all of the other groups’ hands.