Darren Poulson

Long term geek

Jun 042014
 

I recently got a nice parcel turn up at my door; my COM8B R2D2 frame. COM8 frames are one of the standard frames that are used by the R2 Builders club, with a number of different variations. I got the B, or budget, frame which is just a bare bones with nothing fancy to it.

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The frame is really easy to assemble, as it is well machined and comes with some easy to follow instructions. It took less than an hour to put it all together, and at the end of it I had a nice looking frame. It also comes with handy mounting points for electronics. Some of the other features include a nice bracket for the dome motor, spring loaded to ensure a decent connection between the drive wheel or cog, and the dome. I’m just waiting for the charge bay panel to come through.

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The next step was to work on the skins. I got these at the same time as I got the dome, and its been sitting gathering dust all this time. So far I’ve removed a few of the panels from the inner skins, but still have a lot more to cut out. Some of the seams are very thin, too thin for a hacksaw, so I have to be very careful with the cutting out. I may have to resort to the dremel to do these parts, but I’m loathe to do that as it could end up being very messy. There are some panels to remove from the front inner skin that aren’t pre-scored much like some of the inner dome was, so these need to be marked out and cut.

For now I have drilled some of the mounting holes to attach the inner skin to the frame to give it a test fit. There are small 2mm gaps where the skins don’t meet, but from looking at other photos this is fairly standard and once the legs are on they hopefully won’t be noticed. I may end up filling them in a bit.

Test fit of front skins, both layers. Lots to cut out on both layers.

Test fit of inner rear skin. Need to cut out the rear door.

I’m just waiting for a nice day one weekend to finish the dome and do some cutting on the skins. Just a couple of holes to cut in dome, and a whole load of filing and sanding to make things fit properly. I have the hinges now so can start glueing those in and making the flaps work.

Slow progress, but it is at least progress

Apr 052014
 

So, I’ve had my solar panels for a year now, and have just received my fourth cheque from British Gas for my Feed in Tariff and Export Tariff. So, in a year of having the panels, just those cheques alone have come to over £400, and that doesn’t take into account the money saved on my electric bills. British Gas have some nice tools for viewing usage, and from the following graph you can see just just how much my electric consumption went down compared to the previous year.

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Summer months of course were extra good, especially July where I actually consumed next to nothing off the grid. Even the winter months show a little improvement. Rough calculations show my electric bills were approximately £300 less than the previous years.

So, what does this mean? Well, with the FiT money, Export Tariff money, and savings on my electric bill, I’m definitely on track for paying off the solar panels within the predicted 8 years. As electric prices go up, that figure may well improve somewhat too. I’m definitely glad I got them installed, I think it was a fantastic investment and certainly is going to be a better way of saving money in the long run.

Mar 302014
 

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).

IMG_0182To 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 disc grave yard. They really don't last long, and some of the shattered. The larger ones broke in the center so were unusable.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.

All the pie panels done now, along with the top HP. The metal on the spun domes is a fair bit thicker at the top. Just needs a load of filing and sanding to make smooth and safe.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.

Finally got round to cutting some holes into R2's dome. He now has lights! :)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.

 

Mar 132014
 

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.R2D2_Electronics_Block_Diagram

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.

PDUPower 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. 🙂

Feb 202014
 

Ok, so along with my R2, a side project is something that will hopefully fit inside of R2 and make him even more popular. To reprise his role in Return of the Jedi he will be serving drinks, and not just glasses from a fancy tray bolted to his shoulders. He will be able to mix a drink for you and dispense it into your glass.

The idea is, to have a bunch of reservoirs in a caddy inside R2’s main body, with pipes to an automatic arm that will open a door and raise, allowing you to put your drink under it. My design so far allows for five bottles, with peristaltic pumps from adafruit (via a UK reseller, Phenoptix), some L293D motor drivers, a TLC5940 PWM driver, and an Arduino Pro mini. I still have a long way to go on the design, but I have managed to the main module constructed and the pumps installed. I’ve also got a first revision of the circuit schematic worked out, along with a PCB layout that I’ve ordered from OSHPark.

Pumps

A closeup of the pumps

The main unit is made from a series of laser cut acrylic sheets, with a central threaded rod as the main shaft. The bottle tops still need holes for the tubing to go into, and the lids will be glued to the acrylic. Refilling will be done by removing the bottom plate and unscrewing the bottles. I also need to figure out ideas to check for the fluid level so I get notified when a bottle is nearly empty.

The main control for selecting the drinks will be handled by a Raspberry Pi, talking over i2c to the arduino to control the motors. This will allow me to do an embedded web server for selecting the drinks, depending on what options are available. R2 will also have most of his communication done over i2c which will allow the drinks dispenser tie into that and control the door and dispensing arm. Other future ideas are also having a few spare bottles and QR codes as labels on them so that I can automatically scan them in so that the Pi knows what drinks are available rather than having to key the data in manually.

Main unit

The main unit.

This is my first attempt at doing an actual useful PCB. Probably many errors and will need another couple of revisions, but it is a start. The Schematics and other files can be found on github here:

https://github.com/dpoulson/drinks_dispenser

And if you’re really bored and have money burning a hole in your pocket, then the latest revision of the PCB can be bought at OSHPark:

http://oshpark.com/profiles/DarrenP