Summary August 2008

Summary of work and events for August 2008

Posted by Chris on August 31st, 2008 in Update | No Comments


My Artoo in Bantha Tracks

I almost forgot to post this, my Artoo is in the September 2008 edition of Star Wars Insider / Bantha Tracks.

The photo was taken at the Maker Faire back in May.

Posted by Chris on August 29th, 2008 in Events | 1 Comment

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Maker Faire : Intel Developer Forum

Last Thursday Steve and I where at a the Mini Maker Faire at the Intel Developer Forum in San Francisco.  There were probably close to 30 makers in attendance, ranging from robots and electronics projects to Steampunk musicians.

It was the last night of the show and the party was packed. We got to mingle with some cool people and show off Artoo and a bunch of parts and explain what goes into making your very own droid.

I’m in the computer industry so it was strange to be there as an outsider providing entertainment for the evening. It did allow me to make some obscure jokes about Intel chips that nobody would normally get.

This guy was upset because I didn’t have my transmitter in a bag to hide it from onlookers :)

We did a couple of interviews and TV spots, including this one with Wil Harris from ChannelFlip. I’ve been listening to him for years on Twit and it was fun to finally meet him.

Big thanks to the Make team for inviting us to this event – they really do know how to organize a great show.

More photos in the gallery.

Posted by Chris on August 28th, 2008 in Events | No Comments

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Dome Servo Power Upgrade

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.

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Posted by Chris on August 26th, 2008 in Dome, Electronics | 4 Comments

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VEX RC Controller Decoded

Just read this really cool blog post on decoding the VEX RC signal for use on Arduino or similarly cheap micro-controllers.

Check it out. Looks very straightforward and is probably very similar to what Scott is doing on the Jedi system to decode the signal.

But for those on a budget and want to try their own hand at connecting the VexTX/RX to a microcontroller without having to hope thru an intermediate RX this could be a good solution.

From the post:

The nice this about this, is that all of the channels are on a single line. This makes it very easy to interface with a microprocessor. A quick review of the PPM format:

  • 20 ms total before repeat.
  • Each channel is sent as a high signal followed by a 1 ms low. The width of the high signal determines the value sent. A zeroed channel has a width of 1ms. A full positive channel is 1.5ms and a full negative channel is 0.5 ms.
  • On the Vex there are six channel (The six peaks that you see) for a total of about 12ms buffered by approximately 8 ms.

To interface with a microprocessor, simply plug the output of the receiver into your microprocessor. Send 5V to Vdd and Ground to Vss. Tie the output of the receiver to 5V over about a 10K resistor. Start measuring pulses on that channel. If you measure at least a 6ms low(The buffer) start recording pulses. (These are your data pulses.) Record all six channels and then decode the length of each pulse.

Update: I just got a message from fellow builder Jamie who has also worked on something similar. Here’s a thread over on the Arduino forum.

Posted by Chris on August 26th, 2008 in Electronics | No Comments

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Clone Wars Weekend

I’ve had a busy couple of weeks getting Artoo ready for Clone Wars and attending 3 screening events. Started off with the pre-screening in San Francisco on Monday which was great, followed by the midnight opening on Thursday at the local Theater in San Bruno, then an all day event with the Rebel Legion and 501st down in San Jose for Saturday.

Thursday night was fun, but very quiet with not many people turning out for the midnight showing. Maybe 40 or 50 people tops. I guess the days of blockbusters are long gone :)

I did get to see the movie again, and enjoyed it just as much the second time around. The lip syncing still bugged the hell of of me though.

Saturday was a little busier, but not by much. The Rebel Legion were there in force and throughout the day one or two 501st members popped in and out.

The Rebel Legion did a great job organizing a raffle for each performance giving away t-shirts, figures and other prices to those in attendance.

More photos in the gallery

My 5 second review of the movie:

  • Lots of action.
  • Replacement voice actors did a great job.
  • To me, it’s clearly 3 TV episodes bolted together.
  • Considering it’s TV roots and budget the animation wasn’t bad – but not in the same league as Wall-E or even the much older Toy Story.
  • Somewhat weak plot – why they had to pick a Hutt story for the movie is beyond me.
  • The lip sync issue drove me nut.
  • Inconsistent style for the characters, e.g. Obi-Wan is blocky and jerky where as Asajj Ventress is almost life-like with smooth flowing animation.
  • What’s with the Ziro the Hutt speaking English?
  • Hated the new nicknames banded around, from “Stinky” to “Artoo-ee”. I guess little kids will love it.

Having said all that, I enjoyed it, really looking forward to the weekly TV show. Overall rating a B-.

Couple of technical highlights from the weekend:

  • When I switched to the Futaba, I replaced the original 600 mHa NiCad battery pack with a 2,100 mHa NiMH. Runtime went from just a few hours to over 11 hours. More than enough for a days outing.
  • Periscope worked great with a few minor problems.
  • With so many servos in the dome (8 at the last count), the little 7805 5VDC regulator IC on the power distribution board wasn’t up for the job (it can only deliver 1A at most). It would quickly overheat and shutdown stopping all servos in their tracks, so I had to quickly make a new beefed up power supply on Friday night.
  • The new CTEC keycoder worked out great. I can’t see how I used Artoo without it.

Posted by Chris on August 21st, 2008 in Events | No Comments

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SF Clone Wars Screening

Here’s a couple of photos from the Clone Wars pre-release screening in San Francisco on Monday.

It was a pretty low key event compared to some SW charity premiers we’ve been to in the passed, but we all had a lot of fun hanging out.

I didn’t get many photos as security was tight and we had to hand in our phones and camera.

More photos in the gallery.

Posted by Chris on August 13th, 2008 in Events | No Comments

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Periscope Installed

I’ve been tardy posting updates this last week – been busy trying to get stuff back together for the new Clone Wars movie.

I finally got my periscope installed and functioning. Here’s a short video of it in action

There’s still some small quirks I need to iron out, but I’m pretty close to being done with it (for now). One of the big issues is that everything has to be align perfectly, and taking the dome on and off isn’t as simple as it used to be. What I’ve quickly realized is that with every gadget I add maintenance goes up exponentially.

I repainted the periscope housing after tweaking the curve at the top to match my dome. While I was at it I clean up some spot that I wasn’t happy with

Right now the dome pie panel velcro’s on top of the periscope, but it’s hard to get it to sit flush with so much spring in the velcro. It also very hard to align things perfectly and to get it to stay put. I’m probably going to use magnets instead or even use the small side screws I added. Right now they’re just for show to mimic the ROTJ periscope.

I’m not convinced that the clear lenses look correct either, it’s hard to tell but I suspect the original had a slight frosting to it.

I really need to document the wiring and micro-controller setup for this, but here’s a few overview shots of the periscope installed and there are more in the gallery.

Right now, up/down is manually controlled by the Futaba transmitter, at some point I’ll probably automate this. I also have a small 08M Picaxe micro-controller dedicated to automatically rotating the periscope when it’s fully extended. In addition I have to route 12VDC from the main dome power board back down to the periscope light circuit. The Picaxe and the small mini-servo that rotates everything runs on 5VDC and just taps off of the power for the lift servo.

There are two small micro switches, the first trigger the micro-controller to start randomly turning the periscope when it reaches the top

The second turns on/off the lights when the periscope is raised/lowered

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Posted by Chris on August 12th, 2008 in Dome, Electronics | 2 Comments

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