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 🙂

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.

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.

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

Then new dome motor (a surplus Pittman GM9236) arrived today and I thought I’d share a short video to compare it to the original underpowered GM9413 motor I had been using.

It’s still runs at 12V, so no need to upgrade my electrical system to 24V. It spins a lot faster and definitely has a lot more torque.

Here’s the original GM9413 for comparison.

And finally, here’s a quick side by side shot of the two motors, the GM9236 is on the left. It’s a little bit longer and has a small shaft at the bottom which I think is to connect an encoding wheel to.

It does look like I may end up trying running the Pittman Dome Motor at 24 volts as a test going forward. I can’t see adding a gear at this point in time.

This leads me to my next problem, my battery sub-system is all 12 volts. I’ve had no need for 24 volts in the body as my main drive motors the NPC-2212’s can only run at 12 volts, and everything else is stepped down from 12 volts using Dan’s distribution board.

I know how easy it is to create 24 volts from two 12 volt batteries, which I have and can do with what I have on hand, but configuring in series and then tapping off for 12 volts adds a level of complexity for charging the batteries w/o removing or rewiring each time. There’s also the problem of one battery draining faster.

For those unfamiliar with creating 24 volt from 12 volt batteries, this is a really good site explaining how and some of the problems.

One of the problems he talks about is charging unbalanced batteries in parallel and something called a “Battery Equalizers / Balancers” which can fix this problem. The unbalance comes from the 12 volt tap on a 24 volt system, and the two batteries discharging at different rates.

I’m hoping someone has tried an equalizer in their droid before. I’ve found a lot of information on equalizers, mostly large clunky boxes for RV’s and buses, but there are smaller version out the like this one.

What I’m hoping is to use the 3 12 volt 7amp batteries I’m using right now in parallel, and then combine two of these in series for 24 volts. For charging have a switch/circuit to disconnect/isolate them from anything in the droid and reconfigure just in the parallel state to charge all 3 batteries together.

Tall order I know without causing a short circuit or fire 🙂