If you’ve been following along with the blog you’ll know that the electronics inside the dome have evolved a bit over the last 12 months. I’ve added more stuff, moved to a slip ring system rather than separate batteries, and in general created a wiring setup in the dome that’s not perfect and hard to maintain.

Over the weekend I spent a couple of hours trying to simplify and reworking the dome electronics and thought I’d post something on the path I took to get where I am right now.

I’d originally had the various components like batteries, RF Receiver, RC Receiver, Power Board all laid out on the dome base plate – and routed power up into the actual dome with a detachable “umbilical” cord containing the 9V, 12V and 24V. Inside the dome was a terminal block that the various LED boards attached to.

To regain the space for adding the periscope, fire-extinguisher and other gadgets I then moved to stacking the electronic boards in a carrier – also located on the dome base plate.

But over the last few months I’ve been having problems with loose wires In the dome. I’m using the European style terminals blocks and no matter what I do the wires eventually work loose. Not enough to cause the lights to fail totally, but enough be annoying and make them blink or reset when driving around.

I was going to replace the blocks with the more traditional screw down versions (as shown on the right below) and add crimp terminals to all my wires, but there’s still many points of failure so I decided to try and eliminate the “umbilical” cord all together.

With everything in pieces on my work bench it became obvious I could just move the stacked board assemble up into the dome and just use the slip ring wire to connect directly into the dome.

I added a small acrylic mounting plate to the side of the domes existing mounting system.

Then the stacked board assembly just slips in and holds snug, with some velcro to make sure it doesn’t move, but still allow for easy removal and servicing.

It’s a much cleaner solution, but I’m sure it’ll evolve again as I add more stuff to the dome

Related:

• Mounting Dome Electronics
• Mist / Fire Extinguisher Test
• Dome Internal Mounting Plates

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 🙂

I’m definitely getting into the fun part of the project. I spent part of the evening trying to add a servo to the front holo projector. It was a little more tricky than I thought it was going to be. I’d seen photos and vaguely remember a setup on one of the tables at C4, but until tonight I didn’t understood the nuances of the angles and forces need to move something with a servo, so it was frustrating and fun at the same time.

Most people seem to use the same basic method to move pie panels, doors, holo projectors etc. And that’s to convert servo rotation into a linear movement using a push rod attached to the servo horn.

I’d bought some random mini servos from Tower Hobbies a while ago (Hi-Tec HS-55), and a push rod/linkage assembly from ebay. Problem was the servo was too small to fit the rod attachments. I managed to improvise and this is what I finally came up with

Please ignore the kinks in the rod, it really should be straight, but I’d tried to copy what I’d seen at C4 and got it totally wrong 😀

If I was to do this again I’d probably skip the pre-made assemble and make something in acrylic and parts from the local hardware store.

I also created a short video to summaries and demo the new setup.

As I explain in the video it’s not perfect, and I need to affix the servo more permantely to the dome rather than using velcro and I’m not entirely confident the linkage to the back of the HP will last very long.

The good news the Hi-Tec servo is definitely powerful enough to move the HP and will probably work for the pie panels as well.

I also need to decide if I’m going to add some code to my micro-controller to automate random movement.

See Also:

• Slip Ring Servo Test

I was getting tired of my disorganized electronics in the dome, so I made this little holder that mounts everything cleanly and is easily removed.

It’s just a piece of acrylic bent into a U-shape with an extra L-shaped shelf glued in the middle.

The various electronic boards are velcro’d into place for easy removal and the whole thing attaches to one of the dome ring supports.

Top: Syren10 Speed Controller (Dome Periscope), 12V/24V DC/DC Power Converter
Middle: Power Distribution Board
Bottom: 12 Channel RF Receiver

I secure the wires that run up to the dome to make sure I don’t accidentally pull everything off when the dome is removed

Please ignore the 16 gauge wire as well, I was running short of something lighter but didn’t want to make a special trip to the store.

See also:

• Variable 12-24V Converter

I replaced the failed Pittman dome motor last night, and thought I’d post some pictures of the failed gearbox.

The pen tip is pointing to the failed gear in the center of the picture. The teeth are almost stripped flat.

And this is the new motor opened up and how the gearbox should look. Again the gear in question is in the center of the shot. Notice the teeth!

I’m not confident that it will not fail again, and I may need to look at an alternative. I’m hoping the issue was my failed attempt to use batting tape to line the dome bearing to help with traction, but the gear may have been slowly failing with the constant harsh stop/starts on such a small gear. I know of at least one other builder that had a Pittman dome motor fail in the exact same spot.

I finally got a chance to fully test out my slip ring last night with some servos.

I first had to finish soldering up my little boards that would handle signal routing and power.

Rather than try and explain in words and pictures how the setup works I made this short video to try and give a good overview and show the slip ring in action.

I still need to make little brackets to secure the D sockets to the boards, and decide the best place to locate them in Artoo.

See Also:

• Electrical System Update
• Slip Ring Spin Test
• Slip Ring – Cutting the Frame
• Slip Ring Update
• Slip Rings
• Variable 12-24V Converter

I stripped my first set of gears in a motor this weekend. I was goofing around on the driveway showing Artoo to some neighbors across the street when suddenly the dome stopped working. I heard this really bad crunching noise then a very quiet motor spinning.

I quickly pulled him into the workshop and the dome off to see what was up.

A couple of months ago I had lined the inside track of my dome bearing with some batting tape to help the dome wheel grip. It had been slipping and the resulting noise was very annoying. The tape seemed to be the perfect solution …… until the gearbox failed.

I think what had happened was I’d left R2 sitting in the van all day and when I finally unloaded him the glue on the tape had heated up and when I started to spin the dome it balled up – jamming the wheel and breaking the gearbox.

Gerard had a similar failure trying to fix the squeaky slipping wheel. He’d over tightened the tension spring which stopped the dome the moment the motor stopped – but again this put extra pressure on the gears in the Pittman motor causing them to fail.

So for now I’m back to having a squeaky dome.

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.