Idea for robot arms / prosthetics
James Newton wrote 09/13/2018 at 17:30 • 0 pointsFor people interested in designing low cost robotic arms / prosthetics, a quick crazy idea: Check out "twisted string actuators". Combined with a good joint position encoder (hint: Check out "Dexter Robot Arm" and dig into the magic of the encoders) they can make a very responsive but compliant joint with two smaller DC motors and only one drive transistor per motor! It also provides an easy way to transmit the power from the base (or at least further down) to the upper joints, reducing swung weight and increasing payload.
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https://hackaday.io/project/158628
First application I thought of, immediately in fact, was prosthetics.
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They are nice, but how can they be compliant? You can't backdrive them...
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? How is it that you can't back drive them? You exactly CAN back drive them, in fact, they only keep position against outside influence via a very tight loop between the encoder and the drive motor. The twisted string is putting a force on the joint, not running it to a position, so you have to quickly adjust that force to counter outside influence.
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Not quite sure I get what you mean. Do you suggest using an elastic string?
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The string twists. When you apply force to the joints, the string untwists. The elasticity is in the twisting, not in the string itself.
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