Bonnie Burton shot this video of my Artoo at WonderCon this morning. Enjoy.

Link to the original youtube video.

At the recent Clone Wars events it became clear that the little Power Distribution Board that was supplying power to the dome servos wasn’t going to cut it. It would work for a while, but the onboard 7806 regulator would soon overheated and shut down to protect itself.

I’m not surprised, I currently have 8 servos in the dome, 4 for the pie panels, one for the front Holoprojector, one for a side panel, and two for the periscope – with more to be added. Idle, each requires around 8-10mA, but when active they can easily require an Amp or more under heavy load, which can add up fast when you have a few things going at once.

Space is tight on the power board so it’s hard to add decent heat sinks, and even if I could I wasn’t convinced that the single 7805/ 7806 (which can deliver a maximum of 1Amp) was up to powering all the servos from one IC.

One of the problems with servos is that they can sometimes stick and not return to neutral fully, and will continue to draw more power than necessary. Anyone who’s played with servos will know that if they’re even slightly misaligned or put under stress in the neutral position will cause them to hum (which means they’re drawing more than the normal 8-10mA). I’m pretty sure that’s what happens on some of my dome servos, but not all the time. It’s virtually impossible to adjust them all to be perfect, especially as things can move or shake in a fast spinning dome.

The dome is fed by a 12VDC supply coming up thru the slip ring, and servo/signals are connected to a custom board at each end of the slip ring. The 12VDC routes to the power distribution board in the dome that then re-creates the various voltages I need, from 5VDC all the way to 24VDC.

The solution to the servo power/overheating problem is to use a better DC regulator to replace the 7806, but I had a bunch of events coming up fast, was short on time and resource, and basically needed to fix the problem overnight.

So I create a simple power board with parts I had on hand, including three 7805 regulators which would power only 4 servos each, plus I added a big heat sinks on each one and a fan to help keep them cool.

Here’s the board coupled with the original servo board. It’s somewhat clunky and I will replace it at some point with a more streamlined solution and a single better regulator, but for now it worked fine to get me thru the events.

If you’re interested in makng your own servo power supply or even a fully blown Power Distrubution Board, it can be done for not much money. 7805 regulators are easy to find, most surplus stores carry them for around 50c, or at a pinch you can pick them up at RadioShack for under $2. Versions that can deliver higher loads are also available, but can be harder to find or sometimes a lot more expensive.

Google on “7805 circuit” or “7805 power supply” you will find dozens of examples of simple circuits to make your own boards. Here’s a good example.

The regulators also come in 6, 8, 9 and 12V varieties. So as I said you could make a distribution board for not much money if you’re up to the challenge.

I also have to stress again that I’m not an electronics expert. Please double check anything before trying to copy me. In this case there are definitely better was to ‘fix’ this problem.

Related:

• Electrical System Update
• Slip Ring Spin Test
• Slip Ring – Cutting the Frame
• Slip Ring Update
• Slip Rings
• Variable 12-24V Converter

Here’s my latest short video tutorial, this time it’s on cutting your inner dome holes.

This was one of the first things I worked on a year ago, and I’ve finally mastered video editing enough to put something like this together.

Enjoy.

Related Posts:

• First Dome Hole Cut

I got a lot done this weekend. All the major/required holes are now drilled out and test fitting of all the bits that poke through.

Took my time on the last hole, the back PSI, as there wasn’t any room for error. I used the same hole cutter method as before but went extra slow and double checked all my measurements.

I also installed all the holoprojectors with some screws that go through the inner dome.

I still need to JB weld the screws in and I’m not sure if I’m happy with the result. I’m worried that the screws may eventually give out or pull through the dome.

I got to work on some of the electronics and made up some quick housing for the PSI circuits. Nothing fancy just some 1 1/4″ PVC pipe couplers and end stops/plugs. I cut down/sanded the plug make it easier to remove, and added a slot to feed the wires in. I also stuffed the tube with some bubble wrap to help diffuse the light. Eventually I’ll change the wire and hotglue the circuit board into the cap/plug.

I was anxious to do a full test fit of all the dome parts installed, so here’s a quick photo of th rear logic and a holoprojector installed

Here’s a test video of the rear logic and psi in action (ignore the wrong color on the PSI 🙂 )

Now I need to cut out the final outer dome panels and start thinking about painting.

I guess I also need to decide if I’m going to cut the remaining pie panels to make them open.

After a lot of thinking and consulting with Victor and Calvin I decide I’m pretty much done with the dome sanding/fitting. There’s some minor gaps but I can tweak them later and some may work themselves out for various reasons and decisions later.

I think I’ve been procrastinating and using the gaps as an excuse not to starting cutting some holes, so tonight was the night.

I started off with an easy one – the front holoprojector. It went a lot quicker and easier than I’d thought and the result was excellent if I do say so myself.

Basic Steps

• Overlay outer dome and mark circle.
• Find center of circle using some quick math.
• Decide on diameter of hole to cut and first mark with a compass then set the drill hole cutting tool the same.
• Double check slightly larger marked hole with outer dome again.
• Center punch hole.
• Drill pilot hole.
• Drill hole the same size as drill cutting tool bit.
• Start cutting.
• At some point I broke thru on some spots so stopped.
• Dremeled pie wedges using a reinforced cut-off wheel and snapped off the pieces when done.
• File off burrs, hold breath and test fit.

That’s it, and to be honest it was pretty easy really. I’d decide to make the hole exactly the same diameter as the outer hole. If I screwed up I figured I could always sand/file it bigger, but making it too big might be a problem. The holoprojector fit perfectly and a quick test fit of the dome looked really good.

Check out this video of my wobbling/bobbing drill bit.

I was about to drill another when the battery died on my cordless drill, so I’ll have to wait till tomorrow now.