Electrical System Update

The last couple of weeks I’ve been busy getting Artoo back together for a couple of important events. I’ve totally overhauled the electrical system (again) and I’m hoping this will be it for a while.

At the hospital visit on Saturday I ran Artoo for about 4-5 hours on the new system and the 18Ah batteries without any sign of slow down, and I continued to run him again the next day for few more hours on the same charge. I must admit that I didn’t do lots of long sprints, but I’m confident that my earlier battery problems are fixed.

With that said, here’s a summary of the electrical work and the new electrical system design.

The following schematic outlines the 3 main areas of my setup. The red area is the front charging port, flashing LEDs and the battery select/on/off switch. Yellow is the wiring harness/relays that does all the magic of switch batteries between charing mode or running the droid, and finally the blue on the right is the rear electrical panel containing the speed controllers, fuse block, battery monitor, and power distribution board. It also contains an additional relay/power jack to run the drive from 120VAC/12VDC adapter.

There’s also a PDF version that maybe easier for printing.

Here’s a photo of the battery select relay/wiring harness (yellow section of the schematic). It uses 3 automotive relays to do the battery switching for charging and to turn Artoo on and off.

I attached the wiring harness to the battery holder using a small bracket

And here’s the new batteries in place

This is the front charing port (red section on the schematic) you’ve probably seen before. The attaced board to the right is the PICAXE controller that flashes the lights when the front door opens, and the smaller board to the left just contains a 7805 5VDC regular to power the PICAXE. The wiring harness above connects to to the charging socket.

In addition to adding the extra relays to switch two sets of batteries, I replaced the large MAXI fuse block/voltage display with a much smaller ATO fuse block and a separate LED voltage meter display.

I mounted the voltage meter on the rear electrical panel, and instead of using one for each of the batteries I decided to use just one with a switch to flip between batteries. The board requires a separate 5VDC supply to operate and I got this from the power distribution board.

Here’s the new rear panel. Going clockwise, top left is the battery monitor, then the Vex Micro-controller and receiver, below that is the power distribution board, and below that the fuse block, to the left the RoboteQ AX3500 speed controller for the drive motors, and above that the Syren10 speed controller which turn the dome.

I also worked on getting the slip ring soldered up and installed.

And I made up little boards for it to plug into. 12VDC power is connected to the blue terminal block, and the control/servo cables on the 3 pin connectors.

There a very similar board in the dome, but with an additional 5VDC input from a 7805 regulator IC to power the servos.

Posted by Chris on April 21st, 2008 in Electronics | 2 Comments

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Slip Ring Update

I started work on my test slip ring tonight and hope to get it installed in the next few days and report back on a new group order.

The sample slip ring has eighteen 2A circuits and I plan on grouping together 6 or 8 for the +/- 12VDC uplink to the dome, leaving ten circuits for PWM/servo signals. To save on circuits I’m not planning on routing the +/- 5VDC from each of the PWM pairs through the slip ring. As a result each RC channel will require just one wire allocated on the slip ring. I’ll just tap of the 12VDC in the dome and re-create a separate 5VDC supply for the servos.

Out of the box the slip ring wires are loose and really needed protecting.

I bought some braided expandable nylon wire wrap from a local surplus electronics store for less than a dollar.

I wrapped the ends in electrical tape to hold things in place.

Now that I have the wire wrap in place I can start soldering the wires to the connectors.

Here’s an overview video on how I plan to implement the wiring

Posted by Chris on April 14th, 2008 in Dome, Electronics | 4 Comments

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Charging Jack Photos

Here’s a couple of shots of my “finished” charging port and bracket and the associated wiring and electronics before I mounted it. I say “finished”, because I’m currently redesigning the circuit again to accommodate for charging two sets of batteries to work around the RoboteQ problem I experienced at WonderCon.

I ended up soldering the LED array to a small board. They were okay as standalone strings, but mounting them permanently to the bracket was easier this way. The ribbon cable on the left runs to the PICAXE board, and I braced it to make sure the wires wouldn’t pull out

Here it is installed in back of the port bracket

I added a length of acrylic to the original aluminum bracket to mount the additional electronics on it

Here’s the PICAXE board mounted. It drives the LED array

Almost done. I wired in the relay and switch that runs to the main fuse block and batteries.

The relay is hard to see, but click on the image to see the large image and the relay is on the top right of the photo

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Posted by Chris on March 9th, 2008 in Electronics | 1 Comment

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Charging Jack LEDs

I’ve been busy most evenings this month getting ready for WonderCon, but thought I’d stop and post this new addition which I’ve been working on and off for a while now.

I’ve expanded my battery charging port to include some LEDs. The flashing pattern is based on the scene in ESB where Luke and Artoo meet Yoda for the first time.

The whole thing is driven by a 18X Picaxe board with some custom code. I’d originally planned on using some simple timer IC’s, but thought this would be a good project to experiment with Picaxe.

I’ve tried to capture the LED sequence the best I could, but it’s only shown straight on for 10 seconds, and even then it’s obscured by the door some of the time.

To get to this point I had to create a new acrylic mounting plate. I still need to wire in the new charging circuit Bob helped me redesign, but this was the first step in the process.

I went through several iterations and prototypes to get it to fit and work around the Robart hinges. Hence the slots on the left hand side.

I’m hoping to fix it to the 12V charging socket and use it to mount to the metal bracket I made a few weeks ago as part of the original charging circuit.

It’s also been a steep learning curve the as I’ve not really done any major thinking about complicated electronics in a very long time.

I’ll try and post more details in a few weeks, but here’s the completed circuit after a few late nights. I may switch to a smaller Picaxe, like the 08M, as the 18X is a little bit of an overkill for this project. But the price is negotiable in the grand scheme of building a droid. I’d have to guess the whole circuit costs less $35, but in the process I had to buy a bunch of stuff to figure out how to get it to work.

Here’s a a close up of the LED matrix connected to the PICAXE board.

I also had to create a voltage regulator circuit to power everything directly from the batteries as the main power distribution board will be isolated/turned off when the batteries are charging – and the whole point is for R2 to show some bling while he’s charging right?

I ended up using a LM7805 which will step down the 12V supply to the require 5V.

When I get a chance, the plan is to eventually make the LED’s display the current battery voltage when I press a button as the Picaxe 18X has a built in voltage reader.

Posted by Chris on February 13th, 2008 in Electronics | 9 Comments

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Variable 12-24V Converter

Back when I was thinking about stepping up my Pittman dome motor to 24V, and not wanting to have the extra complication of tying two batteries together to make 24V, I’d ordered some small Voltage Converters from ebay to experiment with.

I’m probably not going to install it for the new Dome motor as it’s working fine at 12V, but I do have a 24V supply in the dome for the rear logic lights. This will allow me to have a single 12V battery and save some weight. There is a loss of energy and battery life due to the conversion, but it’s supposed to be in the 90% range.

Update 5/1/08: Andy tipped me off that these board can also be found here.

Posted by Chris on January 3rd, 2008 in Dome, Electronics | No Comments

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R2 Charging Jack/Socket

I feel like I’m on the home stretch getting R2 back together. Tonight I worked on the electronics a bit more.

I plan on re-install the same three 12V 7Ah batteries. However, when the skins go on it’s going to be hard to charge them. So I’ve devised a simple circuit using some automotive relays to allow me to isolate them from the main electronics with a single switch, and charge from an external plug that will run to my Vector Charger.

I wanted to mimic something similar to how Luke charges R2 on Dagobah. The original plug used is some sort of stereo audio jack, but in real life it would almost certainly short when inserted, so I needed to find an alternative.

ESB R2 - Charging Port

After a lot of browsing various electronic and automotive stores I’ve decided to use a 12V car accessory plug and socket for bunch of reasons –

  • They can easily handle the 10-15A the batteries will pull when charging,
  • It’s hard to short the system when inserting it, even if everything is live,
  • If someone was to accidentally plug him into something unexpected – I’d rather it be a 12V device which is almost guaranteed with this type of plug. I couldn’t say the same if I’d gone with some other type of high-voltage plug,
  • Replacement parts are easy to find if I ever need to make up a new charging cable,
  • Theoretically I could plug-in and charge or run other 12V devices off of R2.

I’m going to install the charging port in the same spot as seen in ESB, and I need to make a shelf to hold everything as there’s no frame behind the hole. I cut a curved piece of aluminum that would become the shelf.

I then bent an angle in it to secure it to the new speaker bracket I made a few days ago.

Everything is held in place with just two 8-32 screws

Originally I was going to use a heavy duty DPDT toggle switch to isolate the batteries

But I had problems finding a suitable switch that would work. The one shown above was to really clunky, hard to toggle and not quite heavy duty enough to handle the potential load the drive motors would pull from the battery. So I opted to use a much smaller switch that would toggle the high load through a few standard 30/40A automotive relays. I’ll probably end up replacing these with 60A relays when I get a chance.

To mount the smaller switch I cut a small piece of acrylic and drilled a few holes that would attach it to the 12V socket plug.

I then heated it up for a few seconds to bend it into shape

I also added a status LED so that I’d know for sure when R2 is switch on

Here’s a shot of the back of the automotive relays that will do the switching. I could have probably just used one and just isolated the positive line, but I decided to play it safe and use a second to switch/isolate the ground line as well.

I’ve just bolted them below the support bracket using the same screws that holds the 12V car socket in place.

This is the setup with all the wiring in place.

When the light is green R2 is on, and the charging port is disabled/isolated from the batteries

When the light is off the charging port is live and connected to the batteries. All electronics in R2 are off and I can safely plug in the charging cable which will glow red to show it’s connected to the batteries.

At some point I may also add some red LEDs inside R2 to mimic what’s seen in the movie.

All that remains is the wiring diagram. This is the hand-draw one I worked from, but I’ll try and come back later and clean it up and verify that it matches my final configuration.

Again note – I’m not an electrical engineer so please double check everything if you’re going to try and implement what I’ve done.

Posted by Chris on December 27th, 2007 in Electronics | 2 Comments

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