Tuesday, April 5, 2011

Building a Gripper Claw Assembly for R2-D2

A year ago, one of the R2 Builders was offering a replica of the gripper claw assembly.  It was a really nicely done piece but I just didn't have the resources at the time to purchase one.  

If you are not familiar with what that device is, this is a screenshot from The Empire Strikes Back, in a scene where R2-D2 is trying to grab a small lamp from Yoda...

Like most things with R2-D2...what a movie prop can do for a scene is very different for a real R2-D2.  What's that mean?  Well, finding the parts and pieces that can extend out that far, motorized and work as seen on the movie is a big challenge.

Several months ago, I stumbled upon an aluminum gripper arm & wrist combination.  It strongly resembled the gripper R2-D2 has.

I found this Dagu Gripper Arm at RobotShop.com  It has the servos pre installed and has one in the open/close mechanism and another for the wrist motion.  Due to the fact the tall doors in R2 are 12 inches tall, to fit with an actuator, the wrist portion would have to go.

I found a Hub Adapter made my Lynx Motion (also from RobotShop) that would fit on the end of the gripper.  The key to all of this working is the Firgelli L16 140mm actuator.  With just under 5 inches of stroke, in the closed position it completely fits in the door way.  Needed to make everything work together was something to go from the actuator to the claw. 

 The opening is a bit too large to thread with a 10-24 tap.  The L16 actuator comes with a thread-on piece for fitting into 10-24 threads.  Too get a snug fit, I had to drill this out with an #7 drill bit (13/64) and tap it with a 1/4-20 tap.

It was a real challenge to secure a round piece into a vice....but using a lot of WD40 and patient work, it eventually worked out.

The coupler I bough from McMaster-Carr.  The female end is 10-24 and the male end is 1/4-20.  I shortened the female side by 4 threads to shorten the distance up for a better fit.

With the coupler installed into the hub, the L16 actuator can thread in now...

Here is how it fits in the door-breadpan that mounts behind the front door...

Total cost is less than $200 and all you have to do is drill and tap one pre-existing hole!

Dagu Gripper Arm ($57)
Firgelli L16 140mm Linear Actuator ($80)
Lynxmotion Aluminum Hub  ($8)
McMaster-Carr M-F Coupler Part # 92499A127 ($9.82)
$155 + shipping/handling/taxes