The Nextgen CS:R Arm Box

The Genesis of the Nextgen CS:R Utility Arm Box

My original Eggcrate Frame was different enough from Dave Everett's Styrene Droid Design that I had to design my own Arm Box so it would fit my frame

Click on the image for a 3D .pdf version of the original arm box.

Full details of the original on my design/assembly web pages at
r2d2.media-conversions.net/body.parts/R2.Arm.Box
This design has a few shortcomings. There was no way to support the sides of the Box - the only attachment point was at the bottom. Height had to be adjusted using layers of plastic as spacers. When I did the design, I assumed that anyone who would want to make the arms move would use mechanical linkages to servos mounted behind the box. I wasn't happy with that design because Jr. Jedi knights like to manhandle anything they can get a hold of on an R2 and a mechanical linkage would get bent.

In January 2014, after some correspondence with R2BC Member Reed Franklin, I worked on printing an InMoov Robotic Hand

While the printing project for Reed was an interesting exercise.
More infomation is at the project's main web site:
http://www.inmoov.fr/
The details of the Hand are at:
http://www.inmoov.fr/hand-and-forarm/
It also shows up on:
http://www.thingiverse.com/thing:17773

One of the things I found useful was the method used to move the fingers of the hand.

The servos for the fingers are located in the wrist. A pulley is fastened to each servo and a pair of kevlar fishing lines is run up to the tips of the fingers.

One thought I had was that I could use a similar mechanism to move the utility arms.

I actually purchased some Kevlar Fishing line. It's used in spear guns and has a 200lb test rating. However, maintaining tension on the kevlar so that it would stay wrapped around the pulleys would be difficult. I also thought about using rubber O rings as drive belts. However, there is nothing to keep the belt from slipping if the utility arm is held by a Jr. Jedi knight. Once registration is lost, getting the arm to into a closed position would require re-calibrating the servo's home position. Finally I settled on using a timing belt. I'd become acquainted with them from my 3D printer design project. r2-3d.media-conversions.net/nextgen/NextGenPrinter The Reprap community makes heavy use of timing belts in their printers. While I'm using GT2 (2mm) belt in my printer I've decided to use GT3 (3mm) belts on the utility arm since the coarser teeth should be easier to print. R2BC Builder ROTOPOD uses timing belts in his Utility Arm Mechanization System available on the R2BC parts forum and via his web site ia-parts.com. I'm hoping I'll need only one belt and that there's enough tension in the belt that a separate tensioning mechanism won't be necessary.

The design of the Nextgen Utility Arm Box follows that of the original one except that the box is now larger and the nextgen frame has been modified to allow it to slide in and out. Not shown are a pair of .040 styrene sheets that will cover tha back of the arm box.

Click on the image for a 3D .pdf version of the original arm box.

While it's not 'screen accurate' one of the things you can do to make your droid "different", without being obvious about it, is to add small features. Since I'm printing the Utility arms anyway (with the GT3 pulley attached) I can also bury a "tunnel" for a pair of wires to provide power to a small Led at the tip of the arm.

Click on the image for a 3D .pdf version of the original arm (hence no GT3) with a tunnel added as an example.
 

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