Wednesday, September 8, 2010

Part 2: Building a computer interface arm for R2-D2

The next piece of the puzzle was a strong enough motor to manipulate the cpu arm.  While the resin arm isn't nearly as heavy as the aluminum one, it still requires a strong motor to move it.

My first thought was to use a 12 volt motor, such as my old dome motor.  However after examining the location, I quickly ruled that out.

I tried a LynxMotion pan/tilt system with a standard servo (55 oz of torque).  The servo couldn't lift and move the arm around.  I tried stronger ones in the same size servo, but still no luck.

My local R/C store suggested a large scale servo.  The servos he had experience with were the ones the r/c car races use.  The gears are all metal and the device has a whopping 18 kg of torque.  I'll save you the math, that's over 630 ounces of torque....39 pounds!

Mounting the servo wasn't too bad, I used some scrap aluminum to make a bracket to the frame.  Positioning was the big thing....we need to make sure we clear the door yet not interfere with the hinges.  As you can see below...we found a good fit...

One problem I had to stay on top of was making sure the arm was perfectly straight.  My resin arm base isn't perfectly flat.  Having one of those miniature levels comes in very handy!

So we have the arm, power antenna and large scale servo.  The next piece I needed was a means to remotely turn the device off and on.

For this I purchased a Dimension Engineering BattleSwitch.

This device receive a signal via the radio receiver to turn power off or on to a device.  I'm currently still working on this part!

So with all the pieces available, it was time to get back to modifying the power antenna to extend the data probe.

The nylon cord reels into the device much like a fishing rod reel.  The end that connects to the antenna has a metal, threaded screw.  Or, they usually do.  Mine...was broken.

What I came up with was using a small anchor screw.  The sides are tapered and the tip has a 6-32 threading on it.

I cut the head off of a 6-32 screw and would use that to thread into the shaft of the data probe.

The power part of the anchor screw would be used to crimp onto the nylon cord.

The next part was to make a mount for the power antenna assembly to fit into the frame.  I used an L-bracket for this.

Here's how it looks mounted up inside the frame.

Next time....I'll detail the next challenge...the tubing and fittings to route the nylon cord through.