Flexy-Hand 2

Author: Gyrobot, published on 2014-07-03

Click this button to get the 3D model

Summary

2nd iteration of the Flexy-Hand. It is now wearable so it can eat at the same table alongside Robohand and the Cyborg Beast

Extra features include :

  • Gauntlet attachment via Filaflex hinges.
  • Two length/widths of gauntlet available.
  • Sculpted palm socket.
  • Discrete internal tendon channels.
  • Adjustable tensioners.
  • Discrete glove attachment channels (or alternative “Chicago Fastener” method).
  • Left and right hand versions.
  • Scaleable.

Let’s get this out there and e-NABLE the future to be better for some people. Bring on the improvements, re-mixes and modifications.
Please read the following article about it too : http://3dprint.com/8122/flexy-hand-2-3d-printed-hand/

This hand was printed on a new Witbox printer kindly donated by Recreus.
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EDIT 20/03/2014 : Added an “Opposable Thumb” version of the body.
EDIT 24/01/2015: Added a Thermoform Gauntlet that can be printed flat in PLA and gently heated to be bent into shape.
EDIT 15/12/2014: Added wide and standard thermoform mesh for the palm area. Very useful for the “Thumbless” versions where velcro attachments becomes more difficult trying to route a thumb through the palm pocket too. This is an excellent example of thermoform PLA : http://www.thingiverse.com/thing:403001
EDIT 18/09/2014 : Added a “Wider Wrist Thumbless” version of the Hand Body.
EDIT 08/09/2014 : Added a “Thumbless” version of the Hand Body, for those that still have a usable thumb.
EDIT 19/08/2014 : Uploaded a Hand Body and Gauntlets (short and long) with a 10mm wider across wrist dimension.
EDIT 12/08/2014 : Added “feet” to the flexible wrist hinge, to help increase the glue surface area.
EDIT 29/07/2014 : Increased the tendon hole diameters from 2mm to 3mm when printed at full scale. To help printing at smaller scales.
EDIT 16/07/2014 : Put hole in base of finger hinge (7.stl) so that it can be inserted into hand body easier.
EDIT 08/07/2014 : Sculpted out the socket more to make it larger.
EDIT 07/07/2014 : Updated the profile of the base hinges for the fingers (7.stl). This new profile, requires less force to close the fingers, yet it is shaped to better aid finger return.
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Video : http://youtu.be/yVvdXgVuwGw
Video : http://youtu.be/-Gsy2TgO08w
Video – Mini Flexy-Hand 2 : http://youtu.be/cFUlxXKbJ0I
Video – Fitting a Palm Glove : http://youtu.be/B0VZqIPkkWY
Video review here : http://youtu.be/ceyZsKzNNpY Thanks to 3DUniverse and Jeremy Simon
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http://www.gyrobot.co.uk
http://www.facebook.com/gyrobotuk

Instructions

Printing :

Please see dimension drawing of the palm socket and scale all the stls to suit your particular size requirements. There are two hand models each with their own wrist measurements, one is 10mm wider wrist than the other.
Print hand body with support, unless you can print overhangs successfully. It may be possible to print this hand body without support by leaning backwards at 45deg. I would like to try this one day soon.
Print finger segments either vertically (as modelled) or horizontally, again, I used support. Fingers and hinges from original Flexy-Hand are exactly the same as this one.
Print Hinge segments without support.
Assemble according to PDF

Hinges :

I modelled for Filaflex which is more elastic than Ninjaflex and other flexible PLA atm. However Ninjaflex does work but it maybe a little harder to assemble hence the hinges that fit into the hand body may need a little extra persuading with a screwdriver etc, maybe with some lubrication that can be washed away, e.g. liquid soap. I printed hinges with no infill and 2 or 3 perimeters (depends on scale) using Slic3r, this makes them nice and “spongy” adjust this if you want stiffer or more flexible hinges. The hinges at the base of the fingers are assembled a certain way round to aid finger return, please see section image to show this. Any issues getting the base hinges in can also be helped by using a craft knife and trimming a little off either the hinge or the body of the hand, YMMV. I find with the thumb base hinges a 45deg angle of attack is best to try and get one corner in first.
You can also cast your own with silicon sealant using the Hinge Mould which I also include here for completeness.

Gauntlet.

This is printable without support.

Thermoform version :

Print in PLA. Once printed in flat mode, gently heat either in boiling water or with lighter/blowtorch, hot air gun etc. to soften, then bend over the gauntlet’s arms to 90 deg. A good idea is to place a towel/cloth over the recipients arm before forming the gauntlet to suit. In this case, I printed off a scan of the recipients arm first. Match the hinge pitch to the printed hand width. Obviously be careful when using heat.

Standard version :

There are two lengths and two widths to suit the different width wrists. The short version uses 1 velcro strap for attachment to the arm, but the longer version has slots for 2.
Connect the gauntlet to the hand by 2 off the “FFX – Flexy-Hinge Wrist.stl”, again in Filaflex. Glue these hinges in place with a strong glue.

Tendons :

Choose either a non stretch tendon cord for a stronger grip, or something more elastic for an adaptive grip (think holding eggs)
Feed each end through the two filament holes in the end of the finger tip. Both ends of the filament should come out of the same hole in the base of the finger tip part (see section image plus photo). Tie off in a none slip knot (left over right then right over left) and snip off one of the excess strand. If tensioned correctly the knot should hide itself in the base hole of the finger tip. Thread the tendon down through the finger segments out of the base of the hand. Tie off at roughly the correct tension onto the gauntlet tensioners, then further adjust with the screws. I suggest M2.5mm machine screws, but it depends on your print quality.

Glove :

I guess a “Velcro” style glove attachment (see Cyborg Beast) is your best bet. Print off the “FFX – Bat_Connection.stl” in Filaflex and snip two parallel slits in the Velcro glove. The slits should be sized and positioned so that the Bat Connection just pushes through the slits and slides into the two channels in the inside of the sculpted out palm. This connects the glove to the hand, see video link in main description. Alternatively, you will notice 4 dimples in the inside of the palm, these dimples are positioned so you can safely drill through the hand avoiding the tendon lines for “Chicago Faster” connection of the glove.

Thermoform Mesh :

I bent the fastener tabs at 90deg first and then screwed the mesh into the palm area. This is tricky but with some small sharp self tapping screws you should be able to screw it the the palm area. I then heated up the mesh gently and evenly with a gas lighter until it becomes soft and pliable but not too hot to burn (emphasis). Once soft I then expanded the mesh upwards with the back of a metal spoon to create room for the user to slip their hands into once cool. A few re-heats later you should have something that would fit the recipient nicely. Don’t heat up the mesh whilst the hand is in the gauntlet, wait for it to become soft but cool enough to be touched before forming it around the recipient. Allow for foam padding.

License: Attribution – Non-Commercial – Share Alike

Tags: amputee, cyborg_beast, e-NABLE, Flexy-Hand, Hand_Amputee, prosthetic, Prosthetic_hand, robohand