Tuesday, September 7, 2010

Part 1: Building a computer interface arm for R2-D2

This project has been quite the process so I am spanning it out over several posts.  I don't want to trim any details or photos that may come in handy in the future.  (Or if someone else wants to see the steps I took and improve upon it!)

First, kudos where appropriate....I wanted to copy what Cory Pacione has in use for his droid.  He made two great YouTube videos that give a broad overview of how the system works.  

The way the computer interface arm works is  R2 would drive up to where the computer plug in would be, open his right (tall) panel, unfold the cpu arm (from vertical to horizontal) then extend the probe to connect to the interface.  Here's a screen shot of how it looked in "The Empire Strikes Back"...

The way Cory made his work was to use a 12 volt motor to pivot the cpu arm out then an automotive power antenna (retractable) to push the tip out, then back.  

One thing I had noticed with how other people had made their setups was they had the cpu arm pointing downward in the body.  In the movie clip, it unfolds with the cpu arm aiming upwards.  It may be that way in the other films but I based mine on the clip from "The Empire Strikes Back".

I had already made a prototype using a servo and a U-shaped pushrod to push and retract the probe.  However, with that setup, a good 6 inches of pushrod was extending from the back of the cpu arm.  This wouldn't fit in the frame as it would make contact with the battery or frame structure.

I was really bummed that this setup wouldn't work.  However, the thin, 4-40 size pushrod was too small for the arm, to look like the movie one, it should be a larger diameter rod.

The next step was to figure out the pieces I would need.  12 volt power antenna, a means to control it  and a motor to pivot the arm up and down.

The power antenna search lead me to eBay.  I found a $9 power antenna assembly from a '99 Mazda Miata.  My thinking was a small car MUST have a small antenna, right?  A week later, I had the antenna and began researching how to power it and use it.

Low and behold, I found a gem of a video tutorial from a Miata guru.  Mike's video demonstrates very nicely how to remove and replace a power antenna.  He was also kind enough to respond to my email inquiry for a schematic of the electrical layout, since my antenna did not include the wiring harness.

After playing the videos, I had a very good working knowledge of how to take apart the assembly, so I did so.  I was hoping to find some wires attached to the plug but instead, found they were soldered directly to the PCB.

I knew which contact went where and the writing on the PCB matched that information.  Lacking the wiring to plug in, I decided to go into McGyver-mode.  I clipped the top of the plastic connector off, bent away the pins that were in the way and carefully soldered wire leads to the contacts.  

Heeding some really good advice from fellow builder Nic Williams, who does know electronics, I re-assembled the power antenna and used a lot of hot glue from a hot glue gun to fill the connector in, re-enforcing the structure.

Next time...I'll go over the motor I decided to use to pivot the assembly and continue the saga!