Here's a quick proof-of-concept for mechanical hand extensions with articulation. I built a 10' or so Optimus Prime suit a couple of years ago, and the proportions made my arms ENTIRELY too short to have my hands where I needed them to be. I could have stuck static hands (just fists or whatever) on the ends, but I thought that would look dumb and not very interactive. SO, here's pretty much how I put together the extensions. The pics that follow are a very quick and dirty mock-up hand (couple of hours) using cheap materials; Substitutions should be made for more durable/ better looking hands.
First off, draw the hand scale that I was looking for. Marked the joints as well, then cut templates out of 3/8 foamboard. Cardboard can be used, ABS, whatever, just keep in mind weight and strength.
Cut the finger joints, and then hot glued in 'hinges' at the joints. I used squares of fiberglass screen material. non-stretch fabric works, nylon hinges, once again whatever suits the job.
To keep the hand open when the fingers are not being bent, I've glued risers on the hand top at each side of the joints at 90 degrees. These pieces weep the fingers from bending back and also give me a place to attach the finger-returns.
The finger returns are rubber bands held under tension with bamboo skewer sections at each end. I used a metal compass to make the guide holes, then pushed the bands through with the end of skewer.
On the palm side of the hand, I had to install something to guide the actuation and also keep the fingers from over-bending. To keep the fingers from bending more than 90 degrees, I hot-glued risers as shown with 45 degree ends on each side of the fingers and at the hand.
To strengthen the risers and create a guide for the actuator lines, I inserted bamboo skewer lengths across each end of the riser sections. I used a metal compass tip to start the holes, then pushed the skewers through before cutting them off with snips.
On this, the fingers are only being actuated by lengths of cotton line. Fishing line, string, a lot of stuff can be used as long as it's strong enough to bend the fingers and it doesn't stretch (big deal). Anyways, I tied lengths of line to the cross-pieces in the end of the fingers and threaded them back through to the hand. I also marked guides and pre-made holes in the palm area for more bamboo guides. The actuator lines need to have a very direct route back from the fingers; the first pic below shows lines drawn in where I planned them to run. I then glued a palm bottom (foamboard) onto the hand, and pushed my bamboo guides through before cutting them down.
I also added the thumb finally, I wanted to glue this at an angle so that the hand would not be completely flat. I tied off the band in the thumb to give it a little more tension. I hot glued this in, then ran the line through the guides and out the wrist.
At this point, the hand could be attached to a costume and used as is. All of the lines can be attached to a T-bar or single ring, allowing all of the fingers and thumb to move together. I prefer individual articulation, so each line was run to an individual finger ring on a glove. Here's a short vid of an articulation test:
07212013010 - YouTube
So there's an articulated hand using stuff around my house. Not the prettiest thing here, but it functions and with stronger materials it can be made to do a bit more. This can of course be skinned in board, foam or fabric to finish. In my Prime arm, the extension section rotated in a tube through the end of the forearm, allowing me to 'twist the wrist' as well as articulate the fingers. That small addition added a lot to the effect.
First off, draw the hand scale that I was looking for. Marked the joints as well, then cut templates out of 3/8 foamboard. Cardboard can be used, ABS, whatever, just keep in mind weight and strength.
Cut the finger joints, and then hot glued in 'hinges' at the joints. I used squares of fiberglass screen material. non-stretch fabric works, nylon hinges, once again whatever suits the job.
To keep the hand open when the fingers are not being bent, I've glued risers on the hand top at each side of the joints at 90 degrees. These pieces weep the fingers from bending back and also give me a place to attach the finger-returns.
The finger returns are rubber bands held under tension with bamboo skewer sections at each end. I used a metal compass to make the guide holes, then pushed the bands through with the end of skewer.
On the palm side of the hand, I had to install something to guide the actuation and also keep the fingers from over-bending. To keep the fingers from bending more than 90 degrees, I hot-glued risers as shown with 45 degree ends on each side of the fingers and at the hand.
To strengthen the risers and create a guide for the actuator lines, I inserted bamboo skewer lengths across each end of the riser sections. I used a metal compass tip to start the holes, then pushed the skewers through before cutting them off with snips.
On this, the fingers are only being actuated by lengths of cotton line. Fishing line, string, a lot of stuff can be used as long as it's strong enough to bend the fingers and it doesn't stretch (big deal). Anyways, I tied lengths of line to the cross-pieces in the end of the fingers and threaded them back through to the hand. I also marked guides and pre-made holes in the palm area for more bamboo guides. The actuator lines need to have a very direct route back from the fingers; the first pic below shows lines drawn in where I planned them to run. I then glued a palm bottom (foamboard) onto the hand, and pushed my bamboo guides through before cutting them down.
I also added the thumb finally, I wanted to glue this at an angle so that the hand would not be completely flat. I tied off the band in the thumb to give it a little more tension. I hot glued this in, then ran the line through the guides and out the wrist.
At this point, the hand could be attached to a costume and used as is. All of the lines can be attached to a T-bar or single ring, allowing all of the fingers and thumb to move together. I prefer individual articulation, so each line was run to an individual finger ring on a glove. Here's a short vid of an articulation test:
07212013010 - YouTube
So there's an articulated hand using stuff around my house. Not the prettiest thing here, but it functions and with stronger materials it can be made to do a bit more. This can of course be skinned in board, foam or fabric to finish. In my Prime arm, the extension section rotated in a tube through the end of the forearm, allowing me to 'twist the wrist' as well as articulate the fingers. That small addition added a lot to the effect.
