10/20/19 Revised palms and whipples for improved action. RECOMMENDED UPGRADE.
10/8/19 Resized elastic holes in digits for better fit.
10/6/19: Fixed Palm D to proper bolt head size. Sorry about the error...
These designs are for a terminal device that can be adapted in a large variety of ways. As a standalone, the fingers can be closed by either wrist, electric or elbow actuated systems. If the maker wants a pure Gripper style hand (elastic pivot thumb to rigid fingers), or active fingers to a rigid thumb (Snap Talon style), the rigid parts desired can merely be glued in place with CA (superglue).
For elbow and electric actuation, the connector at this time is a standard 1/2" Fine thread 1" bolt that will screw into the same size nut on the arm end. An o-ring or other flexible gasket should placed between the two fittings for a bit of shock absorption and a firm grip between the two when fully tightened. This may change if/when better connections systems appear.
For wrist activation, you can print flexible hinges that fit Hybrid Gripper Wrist Talon files between palm and thermoform gauntlet. TPU is good for hinges, O Ring and thumb loop. See post-processing for more information.
There are four basic sizes included: A, child size, B: small adult, C: adult, D: Larger adult. Each one is 10% larger than the one below it.
Thumb = 50%; Fingers and Palm = 25%;
Use a minimum of 3 perimeters and 35% for good strength. For flexible items, use 50 -100% infill with 2 perimeters. When printing the wrist activated device, you will need to use brim to secure it to the build platform.
All of the palm designs are for the Right Hand. If you need a Left Hand, just mirror the .stl in Netfabb or your slicer.
The wrist gauntlet and palm cover files will fit both A and B sizes when thermoformed. C and D sizes have been added.
All of the designs have been "repaired" or made manifold and should print without further work. Each of the various parts should print cleanly without support. Beyond making sure that tendon channels are clear, there is normally very little post-processing.
As the four sizes have been scaled up, all of the various channels become larger. The bolt and thumb hinge mounts remain the same size for all four versions. More files will be added to enhance the system as it evolves.
The holes at the pivot point for the fingers to palm connection will fit a 1.75 mm filament "hinge". This addition greatly enhances finger pull strength. I use some old nylon filament for strength/decreased friction and use a soldering iron to flare the ends. The holes in the 1-2 finger positions are aligned so that a single piece of filament can be used for both if you choose.
Assembly order: First, it is helpful to thermoform the palm cover before mounting the fingers. Then, once everything has been assembled, the palm cover easily fits to protect the internals. Next, mount the thumb to the palm with a length of 1/8" brass tube cut to size. This will be locked in place by the addition of a 3mm cap head bolt and nut, or flared filament or CA (superglue). The thumb should pivot freely.
I use paracord (1/4") for the thumb and it is screwed in place with #6 x 3/8" stainless sheet metal screws. There is a guide hole for the screw on the thumb end. I find using a power driver makes this process Much Easier. Run the paracord through the thumb, attach to the palm. Use the length of the paracord to add tautness, then attach to the thumb. Snip the end close and, if you wish, use a flame to seal the paracord ends.
Essential assembly order: Finger pairs and whipple; elastic bands; filament hinges last.Each finger can be attached as a pair (1 and 2, 3 and 4) through the tendon channels to the center of the palm for elbow or electric mounting. Each pair uses a single tendon that goes from the finger end down to the palm, around the whipple side mounts and back up through the palm into the adjacent finger end. The ends can be secured to the fingers by an aluminum crimp or knot as you choose. Each pair will move as far the individual fingers can when gripping an object. The middle portion of the whipple attaches through the wrist to the elbow tendon or to the motor drive. You will need non-stretch wire for motor drive tendon.
The 1/2" x 1" Fine Thread mounting bolt can be inserted from inside the palm and held in place by the tightening process. If you wish extra build integrity, the bolt can also be epoxied in place. I use JB Weld Quick Set.
For wrist driven devices, the individual finger tendon channels run inside the palm and exit
on top of the hand at the wrist. You will need to use the Hybrid Gripper Wrist Talon palms, flexible palm hinge and thermoform gauntlet combo. TPU works fine for the both the hinges and the flexible loop on the thumb. I secure them with CA (superglue) after they are inserted into place. You can use either a single tendon for each finger or run a tendon loop for each pair of fingers to minimize adjusting hardware at the gauntlet (2 adjusters or 4 for individual).
For the elastic return of the fingers, most standard elastic cord will work. I like 1.2mm "crystal string" (craft supply) but with either you can use a large knot to secure to fingers/palm. It helps to have a bit of tension on the elastic for a crisp return. This isn't that easy, especially with crystal string, and may require a frustrating amount of practice, However, know that it is possible and works great once you grasp the technique. The larger size devices may need a thicker cord to fit larger channels.
After complete assembly, add some friction to the fingers and palm so they can better grip hard objects. I use "Shoe Goo" but you might have a favorite such as silicone or "Tippies" or even a nitrile glove. The holes in the finger tips are designed to give a better hold to whatever friction enhancer you choose, so fill those up and leave a goodly portion on the fingertips for better grip.