7/16/14 RIT Arm Stringing, Handomatic

The RIT fingers finally printed!  We started off the day by sanding the fingers.  Then, we assembled the hand.  Turns out the thumb sticks because of the mess up with the knuckles.  We will probably reprint in.  In order to string the elastic bands, we mocked up and printed 10 small beads (printed in red) to anchor the strings.  Tying the knots was a pain because we didn't know how tight it needed to be, however, we learned it was fine.

Stringing of the elastic bands

Stringing the white strings was much more difficult.  Because the hand was designed for fishing line, the thicker string wouldn't easily go through the holes in the knuckles and palm.  First, we tried using a thin copper wire to pull the string through.  Even the copper wire was too thick for the holes, so we used a light weight fishing line to pull the string through.  This worked beautifully...until we reached the thumb.  As it turns out, the hole that feeds the string from the thumb to the palm has a sharp turn in it.  The string would get caught on the corner, then the line would snap trying to pull it through.  After quite a bit of work and jimmying of the string, it was finally pulled through.

The RIT hand after pulling all 5 strings through the fingers (the strings are white above)

The tensioners printed!

As a result of our struggles stringing the RIT hand, we reached several valuable conclusions about stuff we definitely need to change.

1.  Replace Chicago screws with 3D printed pins

2.  Use less material by making the pieces more "wireframed" (the tricep mount and elbow socket don't need to be solid pieces)

3.  Round the curve in the string tunnel from the thumb to the palm as discussed above

4.  Get rid of beads by adding holes in the palm to tie the elastic bands through (similar to Cyborg Beast design)

5.  Add silicone sleeve around elbow socket

6.  (I'm sure we'll find more problems)

We weren't able to complete assembly today but tomorrow we should be able to string up the tensioners and have a completed arm.

While talking to Frankie today I (Alex) found out that there is web based application created by the e-NABLE community known as Handomatic that aims to allow people to use a web interface to create hand models for printing. This application is still in development but I plan to investigate and possibly contribute code to this project.

Handomatic which is still in development

Hopefully tomorrow we will be able to finish the RIT arm and get back to working on more Cyborg Beast designs, but that's all for today!

Alex + Sam