Update 4/21/08: Click here for the latest wiring schematic.

Here’s another revised version of my 12V battery and charging system. I’m now using additional relays to isolate two sets of batteries which can be charged independently.

I’ve also added a little bit more detail to the schematic to show additional connected sub-systems.

There’s also a PDF version available for you to download and print.

Related Posts:

• Updated Charging Circuit

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

Related Posts:

• Battery Power Issues Resolved
• Charging Jack LEDs
• Updated Charging Circuit
• Relays for Charging System

Here’s something small I added right before WonderCon. It’s nothing fancy, but comes in handy when trying to work inside Artoo in the field.

It’s just a row of 3 square LEDs with a small momentary on/off switch.

It’s just duct taped to the underside of the middle shelf for easy removal and runs off of Artoo’s 12VDC supply.

If you’re going to put any sort of electronics in your droid and new to it, then it’s hard to know where to start. Often you’ll be assembling from a kit.

This is a great primer on circuit building, it cover the basics from recommended tools, how to correctly solder and what order you should do things in.

Instructable.com has a lot of great articles that most droid builders could use.

Link

WonderCon was last weekend, and it was my first real test of Artoo since the rebuild. I’d mentioned that both Gerard and I had problems with our batteries. We’d figured it much be the carpet, but I hadn’t had the problem at Celebration 4 – and in the back of my mine I had a niggling theory what was causing it.

For Celebration 4 I’d used 3 7Ah 12V batteries, two dedicated to powering the NPC-2212 drive motors, and one for the body electronics like the sound system, dome drive and speed controllers. But during the rebuild before WonderCon I’d decided to consolidate all 3 batteries into one block to make charging easier. I’d had issues with power before, but thought the problem was resolved and I could consolidate my battery sub-system. Runtime at WonderCon was approx. 60 minutes vs 180+ minutes at C4 – which is a huge difference.

Unfortunately, while I was redesigning my electronics and adding the charging system, I’d forgotten that the RoboteQ speed controller really likes a solid 12V supply, so last weekend as my batteries ran down and when the NPC motors first start-up they were eventually pulling the supply well below the minimum 10.5V required by the controller. It’s “intelligent” and shuts down if it thinks it doesn’t have enough power to control the MOSFET drivers. It’s only for an instant, and starts back up almost immediately as power is cut to the motors – which resulted in the very slow and slightly jerky movement.

So today to prove my theory, I reinstalled the the “dead” batteries from last week without recharging them, and added a separate 12V battery to the Power Control lines on the RoboteQ – Bingo! Worked first time. The issue was totally gone.

I’m kinda embarrassed that I went through this, because I should have remember that there’s a know “design feature” with low batteries and high current draw on this type of speed controller.

I’m now confident that I can pretty much run Artoo for multiple hours on a single charge – but I will have to reconfigure my electronics system again – making it harder to charge batteries in place.

Related Posts:

• WonderCon 2008 Show Report
• Updated Charging System Circuit
• RoboteQ 3500 code 8 fixed
• Artoo’s First Steps

I really like this photo I found of Gerard and I at WonderCon

WC2008-088, originally uploaded by Barry Brown.

Related Posts:

• WonderCon 2008 Show Report

Summary of posts for February 2008

• Rear Door Magnets – after a few different tests this is how i installed my rear panel
• R2 Meets The Doctor
• WonderCon 2008 Show Report
• Some more weight stats
• Back Together – finally got R2 re-assembled and running around.
• Mostly Armless – Artoo’s almost done – we’ll enough for WonderCon at least. Lots more things to work on, but at least he’s now looking like the real deal.
• Charging Jack LEDs – Added some lights to the charging port to simulate what’s seen in ESB.
• Meet R2 Builders at WonderCon – Schedule Posted
• Droid Caller – cheap 75Mhz RC frequency scanner/checker.
• Gary Weaver’s Speeding Bullet
• Fitting Casters for R2’s Center Foot – great video by Mike Senna on how to pick castors for your center foot
• Re-assemble Update

Now that WonderCon is over I’m hoping to go back and post details on the final few steps of my build – I’m probably going to post some things out of order, so you may see some things in the photos that I’ve not covered yet.

First up is the the rear panel/back door. I’d deliberated this for a while and tests a few different methods before finally settling on using the rare earth magnets.

I’d bought a bunch of different sizes, with the intent of using them on various spots on the droid.

One of my fears was the smaller magnets wouldn’t hold, and if I’d went with the larger magnets they’d get in the way of my movable electronics panel, or the door would be impossible to remove.

Frank Cerney had posted a few months ago about using 1/2 inch cylindrical magnets (NSN0818) from Magcraft successfully to hold the door on a wooden frame, so I decided to do something similar. Here’s Frank’s original implementation –

I don’t have the luxury of being able to drill holes in a wooden frame, so I needed to come up with something to hold the magnets to the skin. On hindsight maybe I should have gone with square or block magnets instead, but I was stuck with what I had on hand.

After a few experiments I ended up cutting some aluminum U channel into 1 inch chunks and bent them to clamp the magnets.

The gap is slightly narrower than the magnet, and I simply tapped the magnet in making sure they matched the opposite one.

I then took my CA glue and excellerant and glued them to the skins

I could have used epoxy, but I really wanted this to setup quick without worrying about clamps, movement etc. It seems to hold okay, but I still may still go back and re-enforce them with some epoxy at some point.

Here’s the skins/frame assembled showing the final location of the magnets

One of the issue of using the magnets to hold the door on from the sides is that the force pulls outward, instead of pulling or holding the door tight toward the frame/skin, like if I’d used screws to hold it in place.

You probably can’t tell from the photo, but this results in the door,which naturally curves a little tighter than frame, to bow out at the top.

To combat this I added a tab which will pull everything together and hopefully add a little more hold and reduce the strain on the magnets.

Again I used CA glue to hold it in place

I topped everything off by added some white tape to the inside line of the skins.

Remember I’d had a problem closing the gap at the bottom of the door once I’d cut it from the skins, so rather than fight with it – I simply masked the problem by covering the raw aluminum which blended the door into the skin. I have to thank my wife for this suggestion.

Due to the electronics panel having to swing out I had to either attach the rear power coupler to the door or make it removable from the frame. I opted for the latter as I didn’t want additional weight on the door.

I simply cut a chunk of metal (not aluminum) and secured it to the back of the power coupler. I then used a large magnet on a bracket on the frame to secure the power coupler and allow me to pull it off when needed

The good news is the door holds on great and I had zero problems with it at WonderCon – it even held on even when I did the R2 death spin 🙂