Flexy Hand Reloaded by Rhadamanthys76

Last crawled date: 3 years, 1 month ago

This is basically a mashup of 4 amazing designs already out there
The basic model is Flexy Hand 2, incoporated are Bob Roth's Gimbal mechanism, a slightly modified whipletree and the anchor from Shira's design
This is a specific variant (Left Hand thumbless) since its a model I've been working on for my daughter
Specifics of this design are as follows:
The Gimbal mechnism allows an additional degree of movement - Radial & Ulnar Deviation and in addition has the tendons routed through it so it wont press against the users skin when bending the wrist - this alos allows for more torque
Since my daughter is only 3 years old, I changed some of the geometry of the parts to reduce friction and also the index finger is slightly modified so it bends straight down
The design is made for using crimps for terminations (I'm using #1 single barrel fishing crimps)
The other change is the fingertips. The Lee Tippi microgel fingertips that e-NABLE hands use dont come in sizes this small, so I decided to experiment
The fingertips are in 2 parts. One to be printed in regular PLA
The second flexible portion is supposed to provide the grip without losing the original shape of the finger

Fingertips
These could be printed directly, however I only have access to Filaflex and its not tacky enough to provide grip. I've made the cuts straight to allow for printing in case there are any other filaments that could be used
The other option is to use the provided moulds. The moulds are made to use "pourable" material. I have experimented with Smooth-on's Mold Star 15 and had excellent results, the tips come out really soft and tacky (Shore Hardness of 15A versus Filaflex @ 85A)
I tried to make the hinges with the same material but its too soft - I'm waiting for an order of Moldstar 30 (which is slightly harder) to test that out
Silicone works brilliantly for this application and its extremely durable, the only down side I found to this particular brand was that the color cant be changed, its a greenish cyan color - If anyone knows of better pourable silicone for this, I'll be happy to hear suggestions
The other experiment I have pending in this regard is using gelatin mixes to see how that comes out - I'm a little concerned about the low melting point however, if anyone knows of anything you can add to the mix to raise the temp, I'd love to hear about it
Assembly
The Gimbal is spread slightly and slid onto the palm till the pins on the palm pop into place
The Gauntlet is inserted into the gimbal and the printed pin goes in from the top
The Whippletree top (2 pieces) slide into the bottom and a pin is inserted to keep it in place (I sized the holes to dowel pins I had but you could change that and use a paper clip and snip off the excess)
The bottom of the whippletree is tied to a cable, the end of the cable has a crimp that goes through the hole at the base of the gauntlet and wraps around the anchor that you can use to adjust
Each tendon has a crimp at one end that sits in the groove in the fingertip - glue or melted PLA keeps it in place well
The tendon lines are routed through the fingers, palm, gimbal, go through the upper whippletree and terminate in another crimp
Source Files
I've included the Solidworks files used as well as the original Flexy hand SW models (only the left hand thumbless variant though)