RoboGames 2008 Report

I’m really not sure where to start with my RoboGames coverage – the weekend was jammed packed full of interesting people and cool things – like talking with the machinist who worked on the NPC motors many of us use in our droids, to hanging out with the Orb Swarm folks or Grant Imahara from Mythbusters, or getting some inside info from the engineer who maintains the machines that spin our aluminum domes. Artoo even got in on some battle bot action in the arena and lived to tell the tail.

The event is held at Fort Mason in San Francisco each year and attracts thousands of people from all over the world. I was in attendance all 3 days with support from my friend Richard, and Gerard was there on Saturday with his R2.

The games themselves cover everything from the traditional battle bot arena tournaments, to robot soccer and sumo fighting. There are also special categories for art and bar tending robots. Maybe next year I’ll enter Artoo into the latter. In total there were 70 different competitive categories.

Artoo was a big crowd pleaser as usual, and many photos were taken with his admiring fans. My favorite was this one I found on Flickr by inkyhack.

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Posted by Chris on June 19th, 2008 in Events | 2 Comments

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Attaching Battery Boxes

Here’s a quick run down on how I attached the battery boxes to the feet.

I have the steel feet from JAG which include pre-cut key mounting holes for the battery boxes. I’d already fixed screws to the boxes when I cut out the holes for the motors.

But one of the problems with using the screws/key holes is that’s it’s almost impossible to set them correctly to get the boxes to fit (and hold) the boxes tight to the feet. I think if I didn’t have the NPC motors sticking well into the boxes, then the setup would work, but with the motors in place just getting the boxes on is challenge enough – without worrying about the key holes.

The other problem I had was the boxes were not even close to being straight/true, so when the front was tight to the foot the back had a gap, and vis versa. I’d tried tweaking them without much luck.

Originally I’d tried using some large beefy magnets to help fix the boxes to the feet. They kind of worked, but were easily pulled apart and had a problem getting the front and back to sit flat due to the warped boxes.

Gerard gave me a great tip to just screw the box from the back inside to the bottom of the foot – and it worked a treat.

I just held the box in place, marked and drill a hole in the box and thru to the foot

I tapped the hole from the underside of the foot

I’m still using the side key holes as well, but the new screw holds everything in place and stops the boxes from springing away from the feet.

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Posted by Chris on March 27th, 2008 in Feet | No Comments

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Battery Power Issue Resolved

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.

RoboteQ AX3500

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.

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Posted by Chris on March 1st, 2008 in Electronics, RC | 2 Comments

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Relays for Charging System

I’m using simple 12V SPDT automotive relays in my droid to control switching of power between normal operation and the charging system.

Typically automotive relays are 30A/40A, but I felt I needed something a little bit more substantial. I found these 60/80A relays at SkyCraft for less than $5, which is very reasonable. I’d tried to find something local but came up blank.

The only catch is the terminals are 3/8″, instead of the more normal 1/4″, luckily I found some at Pep Boys for a couple of bucks. I’m hoping to work on getting my electronics re-installed this week and i’ll swap these into my setup at the same time.

Posted by Chris on January 23rd, 2008 in Electronics | 1 Comment

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Dome Drive – Possible 24V Solution

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 🙂

Posted by Chris on December 5th, 2007 in Electronics | No Comments

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NPC Battery Box Cut Out Template

Here’s a quick template I created to help mark out the hole in the battery boxes necessary to accommodate the NPC-2212 motors and the JAG/Dave Painter Foot Drive System.

Download and print the file at full size on 8.5″x11″ paper without scaling. I can’t stress enough not to scale or alter the margins.

JAG NPC Battery Box Template

I used a Dremel to cut out the hole and if I had this template to start with I’d probably saved myself a few hours work and a bunch of cutting wheels.

[PDF Template]

Note: Your mileage will most likely vary. This is not an official builders club document but based on my experience in cutting my JAG Battery Boxes. Everyone has a slightly different way of building a droid, so best check then double check all measurement before cutting.

Posted by Chris on November 13th, 2007 in Feet | 2 Comments

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From Feet to Painting

Weather has turned a little cold and we’ve had some rain, so I got to work in the garage this last weekend.

It was a mix bag, from cleaning up space to work to jumping between painting some parts, cutting the skins and fitting the battery boxes and hoses. I also tried to troubleshoot some issues I’m having, like the dome speed rotation, but more of that later.

First up I really needed to make space to totally disassembled R2. I’d been dreading it and a few events throughout the summer kinda gave me an excuse to avoid it. Even though he’s not finished it’s still been fun driving him around and people love him.

So I started off by breaking him down and inspected parts for wear, missing screws etc.

I never did get a coat of undercoat on the center foot before C4, and some surface rust had set in. I was also surprised how well the omniball castor’s have held up given the terrain I’ve run him over.

Center Foot

Center Foot omni ball

A once over with some sandpaper removed the rust from all the center foot parts and I was able to give them a coat paint.

I also inspected my center ankle for any problems. George Luck broke a JAG center ankle right after C4 and I was a little worried about mine, but all the joints looked fine. I’ve heard of two ankles breaking now, and both times the droids had done a long cross country trek for C4. I’m wondering if that’s the problem rather than every day wear and tear. To be on the safe side I had ordered a spare center ankle from Jerry just in case, but hopefully I’ll not need to use it anytime soon 🙂

JAG Ankle - Weld Inspection

Next up, I finally drilled the holes in the outer feet for the Knurled Hose Fittings (KHF). I had a bit of trouble securing the the foot on my drill press, so had to use my cordless hand drill instead, problem was the drill bit would not fit. I had to use my stepping bit instead. I don’t think it like it much as the steel feet are pretty tough – but it got the job done.

The Kurled Hose Fittings only just arrived last week from Doug and they have a nice feature where the hose is easily secured with a screw-in plug.

Knurled Hose Fittings

With the KFL I also got some new braided hoses, but I wasn’t too keen on how gold they were. I much prefer the original copper one’s I got some time ago.

I had to insert some tubing into the braided hoses to make sure they held their shape and secure the hose in place inside the KHF.

Now comes the kicker with the KHF – there’s always a kicker right? They hit the main drive wheel once I got things back together

I even switched out to using regular nuts, but it looks like I’ll need to trim the KHF’s down by half

I decided to move on to cutting the back of the battery boxes to accommodated the big NPC motors. I couldn’t find a template anywhere, so it was a bit of trial and error. I started off with cutting the smallest hole I could, traced from the matching hole in the foot. It wasn’t big enough to slide down and over the motor so I gradually made things bigger until thinks worked. Once the box is in place you’ll not be able to notice the hole.

I’ll try and create a PDF template later tonight to share [update – here’s the template]

Cut Battery Boxes

I also had to grind down the motor in three spots. In the Dave Painter tutorial it looks like you only need to grind the top sides of the motor, but I also had to grind the bottom outside edge too

So here’s the first foot assembled with the motor encased in the battery box ready for painting. Next step battery harnesses.

As I said at the start of this blog entry, I did a lot more on R2 over the weekend, but I’ll stop here for now.

As always more photos in the gallery section.

Posted by Chris on November 13th, 2007 in Feet, Finish/Paint | 6 Comments

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Hiding Drive Wires

Here’s another retroactive post about something I worked on a few months ago.

One of the challenges is passing the drive wires that goes from the ankle into the foot shell. Some people use the totally hidden/invisible method where slots are cut in the side of the ankle and foot shell very close to the bolt. Here’s an example of Wayne O’s setup using this method.

Space is tight and things have to be perfectly aligned or you run the risk of chopping the wires when the ankle pivots. It’s also virtually impossible to add grommets so over time my worry is that the wire may wear. edit 9/7/07 – Wayne just informed me that his setup above has been working fine for over a year and half without any problems or wear and tear.

I was on a time crunch and not sure if I was up to marking and cutting such precise slots, so I opted for the more conventional method of drilling holes in the foot shell just behind the ankle and corresponding hole in bottom of the ankle.

My wires are pretty think and by my calculation I needed a chunky grommet, but I couldn’t find anything suitable so had to improvise. Instead I used a short length of opaque tubing which passes through from the ankle into the leg. Not only does it protecting the wires it also hide them.

This is the inside of the Ankle

And the Foot Shell

Tube passing from the ankle into the foot shell

I also used the same hose in the top of the legs/shoulder to protect the wire as it passes into the body.

Posted by Chris on August 6th, 2007 in Electronics, Feet, Legs | 2 Comments

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