Tuesday, September 14, 2010

Part 3: Building a computer interface arm for R2-D2

Last time we covered the pieces we needed but how to make them all work and function together was proving to me....well....quite the unique challenge!

 The Resin Arm

The cpu interface arm I bought from resinparts.com was a nice part.  However not being aluminum would have some pros and cons.  The pro was it was lighter.  The con was that painting it would be a more difficult challenge since all my paints are for metals.

Also, I did a poor job if drilling a hole directly down the center for a push rod to go into.  I bought an extra long drill bit but installed in my drill press, I had no room for the piece!  I would up using a hand drill and drilled very carefully with the cpu secured in a vice.  3/4th of the way down, the drill bit wandered and exited the base about a half inch off center.

What I wound up doing was boring the hole out to slightly larger than 1/4 inch.  I used the drill press as far as I could go on both ends, using regular drill bits on the drill press.  I then did the remaining section with the hand drill and the long drill bit.

With that done, I used some plumbing tubing that had an outer diameter of 1/4 inch (inner of 5/16).  I essentially used this as a liner of sorts to correct for the original bad drilling.

On the end, I connected the end to a 5/16th to 1/4 inch connector.

Just to do a test fit, I lined up the resin arm on the frame...

Hmmm, so the servo and servo mount will need to be re-located.  Not to mention a cut out made into the frame ring.

My first try at using a large-sized tubing to route from the motor to the resin arm, while impressive looking, didn't work out...

The problem?  Too thick, so it really fought be bent into any shape other than its initial curve.  Also, the nylon cord would curl up inside the tubing.  Something more narrow would be needed to better guide the nylon cord.

What I wound up using was the 5/16 inner/1/4 outer diameter tubing with a an outer layer of addition outer tubing just at the connection points...the antenna and base of resin arm.  Each are secured with a clamp. 

Another thing I wanted to do and nearly forgot...was to paint the silly thing!

I also attempted some detail and trim work....


This was a tough spot to sort out.  The Mazda Miata (1999 model) has a power antenna that has a antenna sensor wire and a pressure switch cutoff.    It took a while to figure out, especially how to get the BattleSwitch to work with it.

It took a few tries to get this right but here is how it went...

On SC goes the positive lead, but you also have to splice in a second wire that goes to the battery positive terminal.

On SC2 goes the antenna sensor wire.  The motor ground wire goes to the battery negative terminal.

With this setup, by default, SC goes to S1.  In this setup, it is essentially "Off", so the power antenna will not move as this is the antenna down position.

When the switched is turned on, SC goes to S1.  This applies power to the antenna sensor, which turns it on.  The antenna then lifts until triggered by a stopper I put inside the arm.  This is detected by the pressure switch and kills power to the antenna.

Turn switch off and the antenna moves into the down position until it hits the bottom stopper, again setting off the pressure switch and powering off.

AND NOW....when all said and done, it works a lot like this YouTube video