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A project log for Raimi's Arm - Bionic Arm for Kids

Open source, high functioning, myoelectric, bionic arm for kids.

Patrick JoycePatrick Joyce 09/07/2016 at 19:010 Comments

Exciting news! I've struggling for months with the design of the fingers on the bionic hand. I haven't been able to get the force needed to operate the finger low enough. I always intended to use tendons to actuate the fingers, and springs or elastic to return the fingers to a straight position. So the actuator has to pull against the return spring as well as the friction within the tendon mechanism. Try as I might, I couldn't get the no load pull weight down below four hundred grams. Very frustrating. It worked, but 400grams just seemed excessive. Then I found the TACT hand online, which uses a combination of tendons and rigid bars to actuate its fingers. It was an epiphany! So I set about designing my own combination actuated bionic finger. After six prototypes, we (I couldn't have done it without Toni, my carer) have got the no load pull weight down to 100 grams. This opened up the possibility of using nano servos as actuators, making each finger individually controllable. So i'm setting about redesigning the hand from scratch – with only four weeks to go before the hackaday prize deadline. Its possible. Just....