Friday, February 28, 2014

Setting up the random HP movement for R2

This is going to be a long, detailed blog post.  

Hope that coffee cup is full!

Back in 2012, I start doodling some ideas on how to articulate the holographic projector (HP).  A few builders had a few clever ways to move the HP around but I wasn't sure that was the right solution for my setup.  

At the time, my HP had an Optoma PK-301 PICO Projector installed behind it.  For that to work, the projector had to be mounted perfectly flush or the projection would be obscured or offset since the HP cone narrows at the end.  R2 showed this off for our Dinner With The Smiley's surprise

The choice boiled down to this:  If I wanted to have random HP movement, I was going to use a lot of space since the entire projector and assembly would have to move around.  However the the HPs weren't made to handle that sort of load and the deeper I thought, the more complicated the solutions became.  (Which is what any R2 Builder can tell you what building a droid is like!)

I decided that the $399 projector could be pulled out of the dome, where it was going to stop being a big target for wary fingers!  Now it was time to come up with a way to get some servos to pivot the HP around.  As the first link shows, I sat down with an aluminum HP, the shroud piece and doodled up some ideas using micro servos.

Which lead to this piece being made on the CNC machine from 0.25 inch thick material.  Recall that the HP is installed into the dome already.  The only thing I have access to are the four 4-40 thread screws that were bonded into dome with JB Weld.  The piece made would use some spacers and couplers to adjust for the best fit on the back of the HP.

Everything looked very promising for fit but I noticed the center hole had to be a little bit wider, by about 0.25".  The edge of the HP was "notching" into the HP Servo mount.  I could've used a slightly longer spacer but it was such a close fit.  I also filed the edge down so even if they did make contact, the right-angle that was causing some friction would be gone.  The cut outs are so that the servo linkage crossed over the exact center of the HP.  In my setup, I'm using one machine screw in the back piece which with me maneuvered around by the two servos.

Initially I used micro-servos and I have to tell you, I really have a love/hate relationship with them.  I've had a lot of failures with them, brand name and no-name types.  I also knew the HP is going to be push/pulled along and I preferred a stronger, standard sized servo to handle this task.

Once the cut outs for the servos were made a bit larger, the servos were installed.  The back of the HP had a hole drilled in (3/32) and I tapped that for a 4-40 machine screw to thread inside and a nylon insert lock nut on the back.  I found a 3 inch screw worked best since I could eventually trim that down as needed.  The servos are using standard R/C linkages from Du-Bro.  From the horn we have the EZ Connector for the push rod.  The push rod is trimmed (4-40 thread) and I used a heavy duty ball link

Its very, very important that you have the servo's neutral position set properly, so the EZ Connector set screw allows you to slide the push rod along until you have it right.  Be sure to use an inexpensive servo tester to help in this process too.  Make sure you have a receiver battery to provide power to the tester and servos!

So this covers the mechanical side of things.  We have the servos attached, the motors centers so that when both are aligned, the HP is straight and level.  If the screws from the dome to HPs are on the short side, there are RC threaded couplers that will thread on and help give a better fit

To attach the HP servo mount to the HP, I slide it over the four screws and opted to use a couple of regular 4-40 nuts.  I just kept twisting I each one until it was snug.  Granted, this is a temporary setup and until you test it out, I wouldn't do anything permanent with lock nuts or Loctite.

In my next entry, we'll cover the software side.  How do we figure out how to move these around?  How do we setup how far the servos can move on each side?  That's next!