Archives March 2014

So, finally got some time on a weekend with nice weather to get outside with the inner dome and my Dremel. Whilst the dome set I got had a laser cut outer dome, the inner one was totally uncut. The aluminium domes come as an inner and outer to allow you to have the indent around each of the panels, and also lets you have a nice lip if you have the panels opening, which is something I want. Of course, this means lots of holes to cut. Any panels that are going to open have to be cut out, as well as all the holes for the lights and holo projectors (HP).

To start off with, all the holes were marked using the laser cut outer dome as a template. HP and light holes were to be the same size as the outer ones, but the opening panels need more of a lip. A tip I learnt from reading other builder’s logs was to use a large washer, and to put the marker pen in the center, then roll it around the edge of the opening. This gives you pretty much a perfect size for the lip. Next comes the scary part.

Cutting the dome! These things aren’t exactly cheap, and even worse they’re quite hard to come by, having to wait for runs to be done of them by the guys in the states. But, its got to be done so I got the Dremel and a whole bunch of fibreglass reinforced cutting discs for it. I needed a lot as the wear down extremely quickly. I went through over two dozen of them just on the dome. Thankfully I got plenty.

I found the easiest way to do it neatly was to do the large part of the cutting with the dremel, at least enough to make a cut a few cm long so that I could get the hacksaw into the hole. The hacksaw made a much cleaner cut with more control. The Dremel had a habit of biting in and running off a bit, which made some of the fine cuts a bit difficult. By far the hardest bits to do were the circles for which I ended up making a load of straight cuts through the center to form a star pattern, then gradually cut each of the prongs off. Once I had the main parts cut I attached all the cuts with a large file to take it to the lines I had drawn.

It took a good few hours to get through everything, but it was worth it. The holes are still a little rough and still need some sanding down with wet and dry. Also the circular holes all need to be made a little bigger. They were originally marked up to be the same size as the outer dome holes, but ideally they need to be at least a few mm bigger, especially the HPs. Another tip that I’ve found on the net is using a glass wine bottle to help with the sanding of the circular holes. Wrapping some wet and dry around the neck, you can sand in a circular motion to get an even hole.

Still left to do are the rear PSI holes, in both the inner and outer domes. It is the one outer hole that wasn’t pre-cut, so I need to be extra careful with the outer part. The current run of laser cut domes are a lot nicer, with the inner and outer ones laser cut and all just about ready to just polish and paint. Also, I think I’ve been fairly lucky with this dome, as a lot of people report having to cut the inner dome in half to get the inner and outer to fit together properly.

Once the last PSI holes are cut I’ll be ready to bind the two domes together permanently, which is another scary one way step. I’m making sure I’ve as much done with them separate as possible to avoid damaging the outer dome with a slip of the Dremel. I still couldn’t resist having a test fit of the two domes and inserting some of the lighting. It looks pretty good.

Next main steps once its all bonded is to install the main radar eye which I’m hoping to bolt on to make it removable, and then I have to source a load of hinges which seem to be either very expensive, or hard to find.

All in all, a good weekend of work. I would’ve like to do more but due to losing an hour due to the clocks changing, an early morning call from work, and Mother’s Day, I didn’t have much time on the Sunday to do much. Fingers crossed for nice weather again next week to finish off the Dremel work outside. I might also make a start on the skins too.

So, I seem to be building R2 in the reverse of how most people build their versions. Whilst I started with the dome due to finding a good deal, I’ve spent most of my time working on his internals and very little on the actual physical droid. Since my last post back in August regarding R2’s brain, I’ve done a lot of work on how everything will tie together to do the control. My current working idea is to have an i2c bus running throughout as R2’s central nervous system both sending out commands, and receiving feedback.

The main control is still going to be a Raspberry Pi as this gives me much more range to do some interesting things later such as voice recognition, as well as letting me experiment with lots of different ways to actually control R2. I’m still thinking of using a PS3 controller as input, but also thinking of using a wii nunchuck is possible as a much smaller one to control simple operations.

The Pi will be linked via i2c to the various modules such as the servo controllers mentioned in my last post, with one in the dome and one in the body, and also to the lighting systems with Arduinos programmed to receive the signals to trigger various effects. I’m using BHD‘s Arduino code for the TeeCees lights in the dome at the moment, with just minor changes to accept the i2c signals. I may write something at a later date to do more dynamic light displays such as free form text messages to scroll across the RLD, but for now this is more than adequate.

Communication between the spinning dome and body will be through a 6 wire slip ring connector. 2 wires will be enough for the data signal, and then I will pair up the others to provide the power. I’ll probably have to go for two separate 5V supplies to the dome, one for electronics and one for servos as there will more than likely be a lot of noise coming over the servo power lines as they move.

Power for all the electronics will come from a simple USB battery pack, which in turn will be plugged into the power distribution board I have designed. The PDU will take in a raw input from the sealed lead acid battery (or batteries) and produce clean 5v and 12v outputs, as well as a raw output direct to the speed controllers. The PDU also incorporates a few other features such as connectors for volt/amp meters that will be behind a panel on the front of R2, a voltage divider to allow the charge bay lights to function as a crude charge display for the batteries, and also a relay cut off for recharging R2. The last means that I can safely plug R2 into the charger (via an XLR connector), which will pull power going to the rest of the circuits. Lastly, there is the main power switch to kill power from the battery. There is a diode across the switch however which should allow any charge coming from the speed controllers to go back into the battery. This is a feature of the speed controllers to allow regenerative breaking.

The clean 12v will be used to power the audio amplifier. What is R2 without a few beeps and whistles?

I’m just waiting on the PCBs to come back from OSHPark, so I can try them out. Hopefully I managed to get most of it right and I haven’t seriously miscalculated the current draw from the batteries. I don’t want any tracks melting off the board!

Code wise, I’ve done quite a drastic rewrite of the controlling software to make it much more object oriented. Each different module (servos, audio, lights, etc.) is a module with a command keyword associated with it. This means adding new modules (LCD screen, extra lighting, drinks dispenser…) should be easy and just a case of creating a config file and possibly a class file if its a new type of module. All the code is available at github, along with the schematics and board diagrams of the PDU. The PDU is also available to get direct from OSHPark.

Fingers crossed I may be getting a few parts to build the actual droid with soon, including the feet, which means I now have to figure out a drive system for him. Mechanics isn’t exactly my strong suit, so should be interesting. 🙂