Just read this really cool blog post on decoding the VEX RC signal for use on Arduino or similarly cheap micro-controllers.

Check it out. Looks very straightforward and is probably very similar to what Scott is doing on the Jedi system to decode the signal.

But for those on a budget and want to try their own hand at connecting the VexTX/RX to a microcontroller without having to hope thru an intermediate RX this could be a good solution.

From the post:

The nice this about this, is that all of the channels are on a single line. This makes it very easy to interface with a microprocessor. A quick review of the PPM format:

• 20 ms total before repeat.
• Each channel is sent as a high signal followed by a 1 ms low. The width of the high signal determines the value sent. A zeroed channel has a width of 1ms. A full positive channel is 1.5ms and a full negative channel is 0.5 ms.
• On the Vex there are six channel (The six peaks that you see) for a total of about 12ms buffered by approximately 8 ms.

To interface with a microprocessor, simply plug the output of the receiver into your microprocessor. Send 5V to Vdd and Ground to Vss. Tie the output of the receiver to 5V over about a 10K resistor. Start measuring pulses on that channel. If you measure at least a 6ms low(The buffer) start recording pulses. (These are your data pulses.) Record all six channels and then decode the length of each pulse.

Update: I just got a message from fellow builder Jamie who has also worked on something similar. Here’s a thread over on the Arduino forum.

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

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.

For those of you following along from the start you’ll know that I’m using the Vex System to control my droid.

Vex was originally a joint venture between IFI Robotics and RadioShack, but they parted ways back in 2006 and IFI took full control of the Vex Labs company.

Recently Vex Labs introduced the second generation Vex system called Vexplorer. On the surface it’s a simpler (and cheaper) design, but does have some cool things in the starter kit like a 2.4 GHz remote camera. The remote transmitter is a lot smaller too, more like a game controller.

It maybe worth checking out if you’re shopping around for a programmable micro-controller to run your droid.

Looks like the micro-controller is NOT programmable. So I can’t see this being much use beyond using it as a standard RC setup.  VexLabs has dubbed the new controller Vex-Blue vs Vex-Red for the original system I use.

Another big step forward tonight and I’m not really sure where to start or if I can remember everything I did.

Maybe it’s easier to say where I’m at – I now have a lot of the electronics installed in the body, from fuse block and power distribution to the speed controllers and sound system. I can now control the dome and periscope from my Vex transmitter and trigger sounds with my RF remote.

There was a lot of stripping of wires, routing them, testing, and moving stuff around to make it all fit on the back panels. I also installed a second Vex in the dome to control the periscope, and eventually it’ll control some servos on the pie-panels.

From the photo it really doesn’t look like a lot but there’s a lot packed in there

I’m now realizing that it may not be a good idea to run R2 around naked / skin-less at C4. I could easily see someone pulling on the wires and frying something.

Here’s a quick demo video as well.

You’ll notice in the video that the periscope doesn’t run up and down smoothly and it chatters. Some of it is due to the speed the motors run at which I can limit in the Vex, but there’s also a lot of play in the lift mech screw system itself which I need to fix somehow.

I still need to wire in the RoboteQ speed controller which will drive the feet, but you can see it at the bottom of the frame.

One problem I noticed again is that the Vex in the dome has problems receiving a signal. This maybe a big show stopper unless I can route the antenna somewhere else.

The 12 channel RF Remote also has a “problem”. The new models have a little speaker/siren on them which makes this awful bleep every time you press a button on the remote – I’m sure for most applications this is fine, but for R2 it’s got to go. You’d think it could be disabled easily, but I can’t find anything. I’m going to have to fix it before it drives me nuts.

With all the dome work yesterday I had time to think about it’s electronics and how I’m going to lay things out.

I’ve seen some people bond the dome ring to the dome, but I don’t think it’s such a good idea for me. For one I’m using the dome base plate that supports the periscope, and I’m thinking I’ll attach other things to it as well. The base plate is also bigger than the ring and it restricts access from the underside, so there would be no way to get in and fix a lot of things.

So the dome will split in two and I know have the dilemma that I’ll need decide where to put some things, either in the base or up in the dome, and then worry about running wires. For example, only the lift mech needs to attach to the dome plate, and it makes sense to put the weighty batteries down there too.

Initially the dome will contain the following this that are powered

• Power Distribution Board – 12v in, 9v, 6v, 12v out
• Front Logic -9v
• Rear Logic – 24v
• PSI’s- 9v x 2
• Holo Projector Lights – 12v x 3
• Vex Controller for Periscope Lift Mech – 6v
• Batteries – 2 x 12v
• Lift Mech Speed Controller – 12v

Later on I’ll be adding a few servos attached to the panels.

I think I’m going mount most everything on the dome base plate and run 3 power lines up into the dome with quick release.

Here’s a rough idea on layout

Big milestone for me tonight. I finally got around to wiring up my dome periscope lift mech to a speed controller and my VexLabs RC setup.

This is my first time wiring up anything like this, so I was a bit apprehensive. The good news is I didn’t pop anything and it worked first time.

I was really surprised on how fast the little motor spun the mech up and down. So fast that the threaded rod squeals a bit. I may have to program in limits on the controller to cap the max speed.

Here’s a quick photo of the test setup and a video

For the test I used a SyRen10 Speed Controller.