Alien Hand

thingiverse

This is what you might call an assistive device - it takes two perfectly good hands to operate one rather feeble, yet strangely appealing device. Inspired by various designs with tentacles (http://www.thingiverse.com/thing:6986, http://www.thingiverse.com/thing:10337, http://www.thingiverse.com/thing:206231), each finger is crafted as a single piece with 12 flexible sections and can be configured in 8,388,608 different ways. I've set up this version with two four-finger (four degree of freedom) fingers and one two-finger (two degree of freedom) thumb. You can actuate particular flexures in a finger by running the tendons through holes in the outside corners, and not activate other flexures by running the tendons through holes in the center. I've biased all three fingers backwards with tendons running along the back side, attached to rubber bands. I've also mounted the fingers on a palm-gripped platform that lets you use both hands to operate the 10 degrees of freedom. As you can see from the video (https://youtu.be/ws8d-CH5kBk), though, moving the fingers will take a bit of practice! I'm hoping someone will print their own and hook it up to a rack of RC servos. Print Settings Printer Brand: Printer: Rafts: Supports: Resolution: Infill: Notes: The flexy fingers are printed in PLA, but ABS or PETG might also work well. Nylon or flexible filaments would probably be too flexible. Print with a 0.4mm line width to make the flexures come out right. Print 3 fingers, one finger base, one hand base, six rings, two pinkie rings, and two thumb rings. Post-Printing Assembly First insert the finger base into the slots in the hand base and glue them together with a few drops of superglue. Place each finger into the slots in the finger base (with the flat side facing inward) and then glue them in place. Be careful not to get any glue into the small holes for routing the tendons. Stringing up the hand requires patience, as does adjusting the tendon lengths. I used 30# test Spectra fishing line, but you can also use heavy duty button thread. First run lines down the back side of each finger through outside holes in the back corners. Tie them off at the top and then tie one end to a rubber band. For the "thumb", I ran two more lines through two sets of outside front corner holes and tied each one to slightly wider thumb rings. For the fingers, I started only halfway up and threaded lines through front outside holes. Tie them off in mid-sections, then attach them to regular or pinkie rings. Next start at the top and tread two more lines through outside front hole sets, but stop when you reach other sets of lines. At this point, route lines through central holes in the lower part of each finger and tie each one to 2 regular rings for middle and ring fingers. Stretch each rubber band a little so that the fingers are biased backwards slightly. Insert the rubber band into one of the notches, loop it over a corner, and adjust as needed.