August 2003

Saturday 2nd August 2003

Not much had happened to the Hog recently because I had spent nice couple of weeks holidaying in the sun on the south west coast of France. However, today I started to paint the Hog's polypropylene panels. Polypropylene normally has a nice shinny finish which paint doesn't stick to too well, so I roughened up the surface with a bit of 200 grade emery cloth before applying the paint. This made all the difference and the paint stuck fast, and even the kids lent a hand with the painting.

Friday 8th August 2003

I had been thinking hard about a safety flipper clamp during the week, which is a mandatory requirement if you enter Robot Wars competitions. My thoughts were to make some sort of bracket that would fit between the ram body and the flipper, and would hold the flipper in the fully "up" position. There was not much room to fit anything too large, so it took a little bit of thinking to decide how I could design a device that could be slid in place, and then clamped so that it wouldn't get pushed away should the flipper fire inadvertently. In the end I decided on a two part device that could be slid in place and then bolted solidly onto the ram shaft, thereby holding it open.

Saturday 9th August 2003

The hog was back in one peace after having painted the chassis, so I decided to give it a test to check all the pneumatics still worked okay.

Everything seemed to function okay so I took it for a little spin in the street since there were no cars around. Things were going well until all of a sudden the hog started to spin by itself, and then smoke came out from the motor controller. I quickly turned the transmitter off and the fail safe feature brought it to a halt with that horrible all too familiar smell of burning electronics. I dismantled the motor controller and found that two branches of the H bridge circuit driving the left wheel had self destructed.

It took five hours to dismantle, and then rebuild the controller, but by late afternoon it was back up and working. It was a bit worrying as to why the controller suddenly decided to blow up because it has been working fine for quite a few months, and I wasn't particularly pushing it today while running up and down the street. Let's hope this was just a one-off fluke after having been disturbed during the rebuild.

I also completed the flipper clamps that will hold the flipper firmly open. I made the clamps fairly strong, but with a potential force of 1200kg from the ram, I think the clamp might bend a bit should the pneumatics fire unexpectedly.

Sunday 10th August 2003

The family was away this weekend so I spent the vast majority of the day working on the Hog's paint job. Rob Englebright from the Killer Carrot team had kindly agreed to paint me a cartoon picture of the Hog for the back of my trailer in exchange for some robot spares.

I'm no artist, but copied the salient features of his cartoon onto the robot. If I do say so myself, I don't think I did a bad job of painting a face and fur. At the end of the day I had only to finish of the bottom panel, where I had painted a rather large pair of red "polka dot" pants. I had cut out the material for furry ears too, so by the end of the day it was looking quite good.

Saturday 16th August 2003

I finished off touching up all the panels and decided to take the Hog for a final test run in the local school playground before the qualifier's round next Friday. The Hog was performing well and there were a few passers-by who stopped to have a chat. I switched off the receiver while I chatted with one, but when I turned it on again after they had gone, NOTHING HAPPENED! The Hog just stayed were it was.

From the fact that I couldn't hear the gyro spinning any more, it made me suspect that there was a power supply problem. Several failure options ran through my mind, but the last thing I expected was a battery failure. The batteries I was using were less that two months old and hadn't seen much battle action, but when I prodded about the electrics with a voltmeter, I found one of them had no voltage at all. It was completely dead. The only option was to order another one quickly and hope it would arrive before I left for the qualifying round this Friday!

Wednesday 20th August 2003

The new batteries arrived so I put them in and checked that I hadn't disturbed anything else during the process. The pneumatics were working fine, as were the electronics. However, after a couple of minutes, the motors suddenly stopped working.

On further investigation I established that there was a crack on the motor controller circuit board that was preventing power getting through to the interface circuits. It was caused by a ferrite cored choke moving under it's own weight as the robot rattled along the road, and eventually this relatively heavy choke cracked the circuit board together with one of the copper tracks. When I had established exactly where the cracks were, I soldered links across the boards and got the controller working again. Superstition has it that things come in threes, so I'm hoping that this broken PCB track, together with the dead battery and blown MOSFETS completed my run of three breakdowns prior to the Robot Wars series 7 event. I can only keep my fingers firmly crossed over the next few days!

And here's a picture of the team with their new T shirts and battle headgear ready for the qualifyers round. Wish us good luck!