R2-D2: Automating the Pie Panels

This update is going to be all about the R2-D2 dome build, specifically the mechanical and electronics portion for automating the pie panels. This was actually one of the most frustrating parts so far. Not because the work was all that hard, but because much of the componentry that is sold flat out does not work as advertised. But more on that in a bit.

As I mentioned in my previous update, I’m using a Raspberry Pi as the centralized brain of the robot, with several Arduinos being the end device in charge of operating most of the servos and motors. Keep in mind though if you go this route that the Arduinos do not carry enough current to operate the servos and motors. You’ll need to wire them directly to power, and only wire the control pin to the Arduino.  I have a tutorial on connecting servos to an Arduino.

Automating the Pie Panels on R2-D2

I’ve purchased some really nice gadgetry (geeky gadgets!) to put inside my R2-D2 robot. I think you’re really going to like what we’ve got going on. I’ve decided to automate four the the five pie panels. The 5th and 6th are a holo projector and the periscope.  I’ll be adding the periscope at some point in the future, and so for today that pie panel will just be attached with industrial two sided tape.

I purchased the ultimate hinges that Kevin Holme makes. These hinges are nice, and I think Kevin does good work.  However, in hindsight I would have just cut my own on the X-Carve CNC I have. The parts are quite expensive, and honestly I think I could have made higher quality ones. Again, no digs against the great product Kevin makes. They’re great. I really like the setup he’s come up with for the linkage.

The pie panel hinges and the dome hinges are all controlled by Hitec 33065S HS-65HB Mighty Karbonite micro servos. These servos are super nice, but they’re not cheap. All metal gears and a lot of torque. I originally tried some cheap SG90 servos and they were just far too clunky and slow. I moved those over to the holo projectors and they work fine in that use case.

So What About My Frustrations?

Ok.  So automating the pie panels is not without frustration. Let me be clear. Some of the components spec’ed at the R2 builder’s club just don’t work right. I don’t know if this is because things change over time or if people are just to lazy to update things after they finish their build. That’s why I decided to do my own build log on R2-D2, so that those of you who follow me can learn from my mistakes, and my findings.

Captive Studs… Grrr.

The first frustration I found is that the captive studs are basically impossible to install with the recommended nylon lock nuts. I just gave up on that idea and ordered split lock washers and standard nuts. The main problem is that as soon as the nylon engages (after about two turns) the captive nut will spin.  There’s no way to hold in place since it is counter sunk on the outside.

I did try using regular nuts to seat the captive studs, but as soon as the nylon engaged they’d just break free after a turn or two.  If you’re really concerned about this you could also use some blue Loctite threadlocker.

The studs and sanding marks are on the inner dome. These will be covered by the polished outer dome and not visible.  Captive studs are incredibly strong and will never fail like might happen with adhesives.

Stuff Not Lining Up

It’s obvious this stuff is made by 20 to 30 different people. Things just don’t go together exactly as advertised and I found my self working on workarounds for design errors. This of course isn’t so much a problem if you make all of the parts yourself.

An example of this is that the ultimate hinges and the cutouts on the dome are just slightly different in shape. This required some minor filing on the dome and the hinges to get things to line up before I could mount them and drill the captive studs.

Another hinge issue is that one of the pie panel hinges and one of the dome panel hinges hit each other in intersect. This is of course no big deal if you’re only automating one or the other. But when you do both, its a mess you have to sort out.

You can see how I had to bend and overlap the hinges here.  And there are still some issues with the linkage hitting each other so they are currently disconnected.  This is why I say I’d just rather have made my own. I could design around this type of issue for a perfect fit.

RELATED: Parts List for Building R2-D2

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