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.

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.

Related Posts:

• WonderCon 2008 Show Report
• Updated Charging System Circuit
• RoboteQ 3500 code 8 fixed
• Artoo’s First Steps

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.

Drive system jerkiness is all fixed. The problem was the AX3500 and not a Vex compatibility issue. The board had a dry joint on the main power control tab which was causing a short. The speed controller thought the battery was low which cause the fail safes to kick in and turn everything off to avoid damaging the Mosfetts.

I’d gone back and forth on the phone with RoboteQ for a few days, and finally they just overnighted me a new board which fixed the problem instantly. While I was removing the cables to send the old board back the tab connector popped off the board totally.

In the process of troubleshooting the problem, they also convinced me to reconfigure my batteries to have a dedicated 12V supply to the board rather than using a single shared 12V supply for everything. They explained that the symptoms I was seeing were very similar to a low battery problem due to the motors drawing too much current.

I’m probably going to keep the batteries separate for now, but will have to rethink the wiring and my fuse block as I was hoping to just get away with one battery feed which also made charging easier.

The real worrisome thing is he’s way too fast and really dangerous. He can zip around at lightning speeds and can plow through most obstacles because of his weight. I may need to have a fast/slow switch.

He’s also shacking himself to pieces and has already dropped several screws.

I received my center foot on Friday and it was the last structural part that I needed to get R2 on all 3 feet. So, my goal for Saturday was to get him running around under his own steam by the end of the day. I still needed to wire in the RoboteQ AX3500 speed controller which controls the drive system.

I added a power strip to the inside of the back mounting plate to connect all the grounds to and set about wiring things up.

I then did some basic tests of the 3500 and noticed something strange. The motor would run for a second then stop for a split second then start again, like it had a slight tremor. Message code on the 3500 status panel flickered from motor direction information to an ‘8′ - which means under or over voltage. I suspect it’s a low battery. I hope it’s not a Vex/RoboteQ incompatibility problem. I suspect I may need to add a second battery dedicated to just controlling the 3500.

I then worked on trying to get the center foot assembled and attached to the frame. But there was a problem, I was missing the pack of hardware. A quick trip to Ace fixed it, but I couldn’t get the exact parts and had to improvise on the standoffs.

Like the outer legs and feet the new foot was a snug and it took some cajoling to get the pivot point to fit.

Now that the center foot/leg was attached I was excited to think I was close to getting him mobile.

However I really shouldn’t have rushed as much as I did. What followed was a bunch of silly mistakes which cost me a lot of time. Luckily no harm was done and I learned a lot in the process.

Even in my haste to get the legs on and the motors hooked up, I’d remembered that I needed to lock the legs somehow. I’m not going to be using the satellite motors to do 2-3-2 at this points, and one of they’re jobs in the design was to lock/hold the legs in place. So I knew I needed to figure something out, but I thought it wouldn’t hurt to skip this step just for now. Boy was I wrong!

At the same time I also had the drive wheels in the back of the feet, and they weren’t always touching the floor. I’d also forgotten to reverse the drive wires on one motor.

As you can imagine his first steps were not pretty to say the least and he jerked around because of the RoboteQ battery problem, and his legs went in opposite directions. It was a total shambles. Luckily I didn’t have the camera handy for a photo.

I also needed to tension the drive belts more which meant that I had to partially disassemble the feet again. I’m beginning to realize it’s a major pain to unscrew so many bits just to fix one thing.

After stripping him back down and fixing the problems and locking his legs back in 3 legged mode I gave him another spin and here he is. He’s super fast, but I really do need to figure out the battery/undervoltage problem that makes him stop/start/jerk.

Once I get the RoboteQ speed controller working correctly this thing is going to scream.

On a tip off from a fellow builder I bought a few of these cheap motors for $45 vs $150 for the NPC-2212’s.

I already had my NPC-2212, but thought these would make for good spares, and apart from the extra holes and a longer drive shaft they’re a perfect match.

The NPC-2212 is on the right with the long leads and the cheap OEM motor on the left. Click on the image for more photos.

They can be found here.

Your mileage may vary!

A couple of people have written and asked how I configured the SyRen10 Speed Controller and how I connected it to Vex Micro controller, so I thought it best to document it here for future reference.

Setup and wiring was very easy, and I simply went through the online SyRen setup wizard and picked logical answers.

As you can see all but dip switch one are set to ON.

And here’s how the controller is connected to the Vex

There’s only 4 other wires needed, 2 to the battery (V+/-) and 2 to the motor (M+/M-)

I did some further testing of the periscope lift mech tonite. Got it partially installed in the dome. Just placed inside on the dome plate to see how much room I had to play with all around.

I was hoping I’d have enough space in there to add a small servo to rotate the periscope as the mech only raises and lowers - But it really doesn’t look like I’ll have the room.
I also need to widen the hole in the dome as the periscope housing touches in several spots.

I think things will improve once I get the housing glued together and more square, but this was a good test to make sure I’m on the right track.

I’m going to sleep on it tonite and try and figure how I can get the thing to rotate - even if it’s just 90 degrees.

As it lowers you can see that it touches the dome.

I’m a total newbie to Radio Control (RC) stuff, and I’ve been searching the net for good articles that focus on robots.

For basic information there’s a lot of good sites out there explaining things like the transmitter, receiver, servos, batteries and frequencies etc. but they focus on RC Car, Planes or Boats, as opposed to Robotics which has it’s own set of issues.

I went to a local hobby shop yesterday hoping to find an expert who could help but didn’t get very far. They specialize in RC planes/cars and I had high hopes, but they were overwhelmed when I tried to explain how many motors and gizmo’s I needed to control in my R2. They did have some good pricing on 6 and 9 channel equipment, but couldn’t help when I started to ask about how to multiplex channels etc. and had no clue when I asked them how noisy the speed controllers they had for sale.

So last night I stumbled upon this great robotic website for newbies. It’s not fancy but it has a LOT of good information I’m trying to read through right now and it’s helped me to start to understand some of the cryptic posts to the R2 Builders Group when people talk about their RC setup. The site even has a great section on 12V vs 24V motors. One note though, the site sells stuff too and I’m not recommending anything they have for sale, just the great FAQs they have.

I also finally opened up my Vex Robotics kit last night, which is a cross between a RC kit and a micro-controller which can be programmed to do functions. It has 6 channels so will cover basic control of an R2, i.e. wwo channels for the drive motors, one for the dome, and three spare for things like Utility Arms, Periscope etc.

I’m still hoping to get into programming it to give R2 some autonomy or ‘life’ e.g. If I ask him to raise the Periscope he’s go through a sequence to raise, it play specific sounds while the thing rotates - as opposed to me having to do all that manually via a remote.

I’ll try and keep this entry current with any good sites I find on Robotic RC info I find.