May 2003

Saturday 3rd May 2003

With the gas bottle now secured in place, I test drove the Hog around the school playground flipping and shoving a variety of tyres. My main CO2 gas bottle was getting a bit low so I couldn't fully charge the robots bottle, but nevertheless I managed to do quite a few flips and one self-right before it finally gave up.

After a good half hours driving the batteries just started to get low, and the performance dropped of, but by this time I had had a good practice session steering the hog. Hog 2 was certainly a lot nippier that Hog 1 because of the over-driven Bosch motors, which actually made it easier to drive as well.

When I got the Hog back home I checked the drive sprocket grub screws and was glad to see that the loctite had kept them in place. However, the sprockets were rattling a fraction on the motor shaft, implying that the dimple the grub screws located into were getting a bit worn.
By coincidence I was speaking with Karl from the Alien team, and he suggested that that the only way to stop the dimples enlarging and finally scoring a grove all around the shaft was to lock the sprocket onto the shaft with a stainless steel pin drilled right though them. I think I will give this a go as I can see this situation getting worse rather than better.

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Wednesday 7th May 2003

I tried to find a source of suitable 3mm stainless steel rod with which to lock the sprockets onto the motor shafts, but was not having much success. Many of the suppliers would happily sell me a bundle of 3mm rod, but I only needed about 50mm worth of rod, not 5 metres!

While wandering around a DIY shop I noticed some masonry nails. These happened to be 3mm in diameter, and I thought they must be strong enough for the job, so bought a small packet of them. When I got them home, I did a few tests by trying to bend them and cut them with a hacksaw, and happily came to the conclusion that they would do the job admirably.

I removed the two motors from the hog and dismantled them so that I could hold the shaft and sprocket in a bench vice ready to be drilled. I was very grateful for the new bench drill that allowed me to drill a perfectly straight hole in both shafts. I then cut a couple of nails down to size and put a small bend in each. This would create enough friction for the pins to remain in place without any further restrain, so after tapping them into position with a hammer, I reassembled the motors.


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Sunday 18th May 2003

I went of test run in the local Infant's school playground, which turned out to be quite a useful exercise today. Several times during the session, the chains jumped off. I came to the conclusion that it was because the axle assemblies skewed around a bit because I was getting more confident at driving, and was pushing the motors harder and faster. It took a little while to realise what was happening, but I think it was because I am only securing the axles in place in one direction. When I am driving in one direction, this is fine. But when I go the other way, the tie rod is no longer working in same direction and there is nothing more than the clamping friction of a bolt and washer holding the bearing in place, hence it tends to move.

I also noticed that the gas bottle ran out fairly quickly. I am using a 1.1kg bottle, but haven't been able to fill it fully despite having just had my main gas supply bottle refilled. This may tempt me into using a 2.2kg bottle if I can squeeze it into the body somehow.
The other thing I noticed was that the nylon wheels at the front of the robot were starting to get a bit worn. Since they have spent most of their life running on tarmac, they take quite a pasting, especially while turning because they are fixed in one direction. Maybe on a nice hardboard floor they would last longer, but in the playground they are wearing very quickly, and the front flipper is starting to drag on the floor. I think I will buy a few more wheels since they are quite cheap, and keep them as spares.
A few of the nuts securing the motor controller box to the chassis had worked themselves loose and fallen off during the drive. I think I'll use locknuts in future to stop then falling off!

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Saturday 24th May 2003

I decided to have a go at securing the axles a bit better by modifying the chain tensioners. This should stop the axles skewing round and causing the chains to just off.

Instead of the chain tensioner just pulling the axle in one direction, I would lock it in both directions, therefore holding the axle no matter whether the Hog was going forward or backwards. The photo shows the additional support and locknuts on both sides.

There were two other major concerns I had about the Hog. The first was to do with that old chestnut weight, and how I was going to reclaim some of it back so that I could use thicker armour. The second was about how long my 1.1kg gas bottle lasted and whether I could afford the extra weight and size of a 2.2kg bottle.

On the weight front, it dawned on me that my batteries were giving me something in the region of 30 minutes of action before showing signs of going flat. Maybe if I used smaller ones I could save a few kgs, so I looked through a few catalogues, and found that a couple of 12ah batteries would save me about 4kg. The size was not too dissimilar, so hopefully I wouldn't have too many changes to make to the battery tray. I bit the bullet and ordered two Yuasa 12ah batteries from CPC.

On the gas bottle front, I thought that all the weight saving I would make using the smaller batteries would be swallowed up if I used a 2.2kg instead of my 1.1kg bottle. To see what the damage would be, I weighed both a 1.1kg bottle and a 2.2kg bottle (the weight referring to the weight of gas contained within the bottles, rather than the weight of the bottles themselves) and was astounded to find the that there was only a fraction of a kg between them. The smaller 1.1kg bottle is obviously made a bit tougher than the 2.2kg fire extinguisher bottle, so as long as I can physically squeeze the 2.2kg bottle within the Hog, I will start work on getting my fire extinguisher bottle pressure tested!

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Saturday 31st May 2003

I received the new smaller batteries during the week, and as the photo shows, there is quite a difference in size. I set about looking at how to fit them into the cradle of their larger predecessor. Luckily it wasn't too much of a task, and I only needed a few changes to the clamps.

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Last updated 2nd june 2003