Slip Ring Servo Test

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.

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Posted by Chris on April 25th, 2008 in Body, Dome, Electronics | 2 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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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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Periscope Port Detail

Here’s something else I’d forgotten I’d worked on before C4 and not posted.

The original dome periscope had a small raised lip around the side ports/windows. Neither my PVC or aluminum periscope kit has this so I improvised.

I used a 1″ Nylon gasket from the plumbing department at my local Ace Hardware store, and just superglued it in place. However, paint has a real hard time adhering to Nylon, so if I was to do this again I’d probably try and find an O ring made from something different. Also if you try and rough up it up you’ll get fine strands that will never go away.

I guess I’m posting this as an idea rather than a solution.

Posted by Chris on January 11th, 2008 in Dome | 1 Comment

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Video Tutorial – Cutting Dome Holes

Here’s my latest short video tutorial, this time it’s on cutting your inner dome holes.

This was one of the first things I worked on a year ago, and I’ve finally mastered video editing enough to put something like this together.


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Posted by Chris on January 4th, 2008 in Dome | 3 Comments

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New Pittman Dome Motor Ordered

Pittman GM9236I’ve continued to do research and testing on my dome drive system, and it does look like I need to change the motor out for something with a bit more humph.

It seem that a few people are happy with driving the recommended GM9413 Pittman motor at 24V instead of 12V with good results, but I really want to avoid introducing the complexity of 24V into my system just for one motor. It will complicate charging the batteries at best and the shorten the system run time between charges, and at worse reduce the overall battery life unnecessarily.

In the last day or so I’ve got a lot of great advice from fellow builders, including a lot of links that helped me decide which new motor to go with. I wanted to stay with a Pittman if I could to hopefully avoid redesigning the dome drive system, and it looks like one of the variations of the Pittman GM9236 would work. It comes in a few different gearings and voltage ratings.

There was one specific 12V version I was shopping around for, the GM2936S018, which delivers about 3 times the torque, and about twice the RPMs of my current motor, but it was around $130, and I’d rather find something a little cheaper if I could. Then Bob pointed me at another GM9236 model that was very similar, but only $23 at a surplus store. They’re used/surplus but probably worth the risk so I ordered one to try. It has very similar specs delivering a lot more torque and hopefully went it’s installed, spin the dome a little faster 🙂

So here’s the links I used for my research and where to find motors

Posted by Chris on December 7th, 2007 in Dome, Electronics | No Comments

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Dome Drive / Pittman Motor

Tonight I’ve started to work on some dome stuff, including the dome drive system which has been bugging me for months.

I’m using Darren’s dome drive kit (based on Atomic Pickle’s) and it uses the Pittman GM9413-2 geared motor. Spec’d at 12v, 19.7:1, 142RPM.

To me it seems sluggish and rotates slowly compared to a lot of other droids I’ve seen, especially when I change direction. It could be the weight of the dome, which is around 17lb with all the accessories. Including all alu parts, like HP’s, surrounds, radar eye, dome ring, and periscope, plus the batteries, smoke/fire-extinguisher etc. etc. But I’m sure I’m not the only one with a heavy dome.

I’m wondering if others are experiences sluggish domes who are using this Pittman either from Darren’s kit or from AP’s? Especially if your dome is heavy?

According to the GM9413-2 data sheet on the AP site, the motor is rated at 12v, which is what I’ve been running it at, but on the motor itself the label says 12/24v.

I’d rather not run it as 24v if I can help it – but if it would help I could re-configure some of my batteries as a last resort.

The only other thing I can think of is the slight sagging in the mounting, but the motor is making full contact with the rockler bearing. Maybe it’s not doing a great job of holding on or maybe pushing too hard against the rockler bearing?

I know many Sennaites are using the Saturn motors at 24v for the dome, but I’d rather not switch class of motors right now. I’ve posted to the Yahoo! Group to see if anyone has some suggestions specific to the Pittman motors.

Edited to add some videos. Here’s the Pittman running at 12v directly off a battery, no speed controller so startup is instant and it looks okay right now which I don’t understand. I’m wondering if it’s a speed controller issue, or maybe even a problem when he’s angled in 3 legged mode. mmm.

And here it is running at 24v – super fast I know, but I’d rather the top speed be fast and I can slow it down with the transmitter/speed controller commands.

Now to troubleshoot why the 12v spin seems okay.

I did some further testing tonight, and held the body at an angle while the dome spun. Man, is there a lot of force whipping around while it turns, even at the slower 12v. I can feel it struggle on the up swing as the two heavier side of the dome comes around. 24v helped a lot but I need to go back and put the speed controller back in the loop to confirm my test and see how snappy it is looking left and right.

Posted by Chris on December 4th, 2007 in Dome, Electronics | 3 Comments

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Dome Switches

I’ve come to the conclusion that external dome bump switches are a bad idea, for events at least.

Dome Bump Switches

I like the convenience of being able to quickly turn off the dome lights to save the battery, but kids quickly work out what they do and are constantly playing with them. They can’t do much damage but i’s very annoying, and I’m leaning toward replacing them with an internal switch even though it’ll be a pain to get at. I’m not sure if I’d leave the dead switches in place or replace them with simple bumps.

If you’re about to go down this route I’d personally recommend against having external switches of any kind.

Posted by Chris on November 14th, 2007 in Dome, Electronics | No Comments

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