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I am currently working on a design for a robotic prosthetic leg for a tortoise who had a rather nasty run in with a fox. This left him with just one full and functioning leg, along with two half legs and one completely missing. This has left him in a state that makes movement rather difficult and certainly uncomfortable for him. For a long while I was trying to figure out how to attach the leg to him as he is still growing so the commonly applied solution for tortoises of epoxy isn't an option. I've now decided on a heat shaped 3D printed mesh that clips over the back of his shell making it easily removable but lightweight and strong. Now I'm onto the leg itself. I'm thinking the best solution would be a 2 jointed leg. Now I am not new to the world of electronics but this is my first stab at any form of prosthetic and if anyone could provide some advice it would be much appreciated. If this goes well I'm hoping to start playing with my own designs for human prosthetics too. The two main questions are, what to use to drive the joints, and how to actually control the motion itself. For the joints, I guess the options are either servos or stepper motors. Now the leg needs to be very compact so whatever I use can't be massive but it needs a good bit of torque. He ways around 2kg in total. Power and control board can be fitted to the shell mount so it is literally the motors/servos that need fitting to his leg. As for how to control it, my two trains of thought were, either A, seeing if I can use muscle sensors to trigger movement when he tried to move his missing leg, or B, using accelerometers which sense when he tries to move forward or backwards and triggers s single cycle of motion in that direction. Option A could pose many problems what with the scale of the project, the thick and scaley nature of a tortoises skin and the inability to actually train it to try using the leg. B seems more straightforward but I'd be interested to hear your opinions. Again, absolutely any help would be much appreciated. Thanks!