Battery Terminals

This is a minor update, but thought it maybe worth posting.

When I swapped out the batteries for the larger 18Ah variety, they had screw down terminals. I knew I’d most likely be removing batteries frequently for charging and really didn’t want to use the screws to secure my cables, so I opted to use spring clips/clamps.

The problem is the spring clamps don’t work all that well, first they don’t hold because they loose their springiness, and then there’s the constant fear of shorting something with such a big plug. I’ve also needed to swap back to my smaller batteries a few times and the clamps just don’t work well on the small terminals.

So, I decided to add small extensions to the battery terminals to go back to using regular crimp connectors.

I may go one step further and shield the exposed terminals – just in case 🙂

Posted by Chris on June 6th, 2008 in Electronics | No Comments

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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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New Battery Holder

I really am building honest and Artoo is back on the workbench.

I’ve revised my battery charging system and in the process of making a new harness for the larger batteries. I’m also reworking my fuse system, so basically everything had to come out. This may look like a mess, but I know where everything goes back honest!

The new battery harness is designed it in such a way that I can mix my old 7ah batteries  and the newer 18ah. I added a little arm that folds out and holds the smaller battery when needed.

Here it is with mixed 18ah and 7ah batteries in place

Arm out of the way and two 18ah batteries this time

Tonite I’m hoping to finish up the re-wiring.

Posted by Chris on April 16th, 2008 in Electronics | No Comments

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Slip Rings

A slip ring, in electrical engineering terms, is a method of making an electrical connection through a rotating assembly.

In our case it could be used to route power and other signals into the dome, but still allow it to rotate continuously without tangling wires.

I’ve been toying with the idea of putting a slip ring in my droid for a couple of reason

  • Remove the needs for extra batteries in the dome and save weight at the same time
  • Easier charging of the batteries
  • I’m upgrading my RC setup to 2.4Ghz in the next month, and this would allow me to eliminate an expensive second receiver in the dome.

Here’s a quick picture of a sample I picked up today.

Slip Ring

It’s pretty small, but offers 18 circuits, each capable of 2A. The company that sells them is close to where I work and they also sell a much smaller 6 circuit design as well as 12 and 24 in the same size package as above.

I plan on testing it out in the next couple of weeks and will report back on my findings.

Posted by Chris on March 27th, 2008 in Electronics | 7 Comments

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Easter Get Together

I can’t believe it’s been a month since WonderCon — I’ve done very little on Artoo since, which as been a nice break, but I feel guilty that I still need to go back and post on work I’d done last month.

The good news is, as a result of us being at WonderCon there’s at least one new builder who’s jumped head first into building. What’s even better he only lives a few miles away from me – Welcome to the club Steve!

Today I did get together with Gerard to talk droid and strip my Artoo back down ready to implement my revised battery system. I was hoping to get a few more local builders over, but being easter it was hard to arrange at such short notice.

The easter bunny also brought me newer bigger batteries. I’m going to replace the smaller 7Ah batteries with a single 12V 18Ah battery. Thanks Gerard!

Now to try and get the battery to fit and still be easily removed.

I’m probably going to position the new battery just off-center with a second smaller standby battery for the RoboteQ to the right. Based on the height of the battery and the clearance needed to get it in and out, the new holder/harness will probably much shorter than my original.

I’m also even more convinced that I should loose the fuse block, which works well and even has a battery voltage read-out, but it’s somewhat overkill and gets in the way of battery removal. I could try putting it deeper into the droid, but that then defeats the purpose of keeping for the voltage display.

In closing here’s shot of my frame minus the skins

Posted by Chris on March 24th, 2008 in Electronics, Events | No 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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Battery Power Issue Resolved

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.

RoboteQ AX3500

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.

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Posted by Chris on March 1st, 2008 in Electronics, RC | 2 Comments

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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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