Stomp - March 1999

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Although we're rushing ahead with the body - amazing aluminium boxes joined together - similar idea for the feet, we're racking our brains about reducing the RPM of any motor so we can step about once a second - maybe a motorbike gearbox.

We're hunting for (cheap!) electric motors Bosch Motors are 24V 800W and only cost £100 each + VAT New! Also, the bigger wheelchair motors that go into shopping scooters and golf caddies could do nicely. Some of the golf caddies have very complex regenerative braking systems. Could save some battery time.

Electric motors seem expensive (or un-reversible). How about petrol? The crucial question is "How long will it run on 6oz (or whatever the limit is) of fuel?". It certainly seems more likely that we'll get a petrol motor with the grunt rather than an electric one. I guess we only need 5 mins of running time. We read the rules and the limits on fuel the lesser of 8 oz. or 6 minutes running time. A few back-of-the-envelope calculations suggest that a 4-hp motor should get through approx. 1 fl. oz. of petrol per minute, so that should be OK. We will have to test this out, of course.

It seems we may be able to get hold of an old petrol mower. It's a suffolk punch. It may be about £30 (actually was free). The new versions of these mowers range in power from 2-5Hp. Some strimmers are 2Hp. The 'typical' new petrol mower is about 3.5Hp. So, hopefully this old one will do.

There are probably many ways of 'maximising' 8oz of fuel. Perhaps we could have very long pipes to and from the tank that are difficult to empty! Yeah, we could have one of those spirally pipes that they always seem to use when building illegal stills! Actually... I seem to recall reading that any internal combustion engine can also burn alcohol, and that it's a cleaner, more efficient fuel; something we should think about.

Perhaps we should check how they measure it. We could hold fuel in the pipes, but they may want to see them empty. They may even insist that we run the engine until it's dry, this would exhaust even the fuel in the float chamber of the carb. How about giving your contact at Robot Wars a call?

Simon built a model of STOMP in Lego Mindstorm. It works! Proof.

After reviewing the materials available, We concluded that the best way to strengthen the feet is to rivet aluminium 'angle' around the open edge. I only have a couple of short pieces of this. We need to find some more.

22nd March:
John collected the mower at the weekend. He got it for nothing in the end, except that, if we get some spectators tickets, he would like two of them. It looks fairly well cared for, except the starting string needs some attention. I got as far as cleaning it up and buying a jerry can of petrol. I'll try to get it going one evening this week. It has two controls: throttle and clutch. The clutch is disengaged when you pull the lever. It has two drives: one to the roller and one to the cutting blades. It's quite heavy, the whole mower probably weighs about 40Kg.

The other thing that John tried to do was to make up some angles out of aluminium sheet. Bad idea. It was impossible to bend the stuff, even with a large hammer. John's mate Pete, the welder from Rolls Royce, told me that Aluminium is very strange stuff to work with. You can Mig weld it, using special rods, but you don't get a pool of metal as you do with iron. It just goes a bit white. If you get it too hot then it just disintergrates completey. If you try to bend it without first anealing it (heating it up), then it will fracture. To get the anealing temperature just right, rub some soap onto the metal. When the soap turns black, the metal is ready for bashing. When trying to cut it with a jig-saw, you need to use some form of coolant, otherwise the metal melts and cloggs-up the blade. I found this out the hard way. Just a few drops of engine oil stops it happening, parafin is apparently what is used in industrial processes.

John saw some nice pieces of aluminium door frames at the tip on Sunday. The bloke wanted £3 for them, but John did not have any change. Something like that could be cut up and used to strengthen the boxes. We really do need to get the metal soon.

Nick (Old Nick - John's brother) has been on business in the middle east. He will check out the crank situation this week. He felt that we should be using bearings for the cranks and that it would be false economy not to. He will look into getting us a good price for some suitable bearings.

Simon had some (weird?!) thoughts on making the robot more efficient and less power hungry. If the heavier bits could be arranged so they move down when the body moves up, the power required would be a fraction of our 3kW.

Is it actually possible to do this?

John thinks that the best we can do on that score is to keep the heavy bits as near to the 'bottom' of the boxes as possible.

John checked out the motor last night and got it running. It sounds like a dumper truck. He might try to cut the lawn with it tonight. He had to rebuild the starter cassette. The spring had come unravelled. It's quite badly worn and tends to stick open, leaving the string hanging out. We might need to consider a trip to the local lawn-mower repair shop for a new one? The other problem is that the only apparent way to stop it, is to whip off the spark plug lead. John's always been too poor to own a petrol mower, does anyone else know how they should be stopped?

The engine is 30cm high and 48cm wide (starter to drive cog). We will probably have to reduce this width by reducing the length of the drive shafts which go in and out of the centrifugal clutch. It's a four stroke side-valve engine. There are no marking to indicate the size or power output of the engine. John's mate David reckoned that on one tank (about 1ltr), he could cut his lawn (40 feet square) 5 times, which sounds amazing.

The basic arangement is that the motor drives one side of the clutch. When the thottle is opened the engine speed picks up and the clutch drives the primary drive sprocket (7 teeth). This sprocket then drives another sprocket (19 teeth) via a spring tensioned chain (bicycle size). The second sprocket drives the shaft with the blades on it. At the other end of the blade shaft is a belt and pulley arrangement which drives the roller. A pulley belt tensioning device is operated by a cable from the handle bars. This allows the power to the rollers to be varied.

31/03:

Email from John to his brother, Nick:
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From: jlilley
Sent: 29 March 1999 13:02
To: nlilley
Subject: Cranks


Nick,
Any news about the cranks?

John
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From: nlilley
Sent: 29 March 1999 13:02
To: jlilley
Subject: Cranks


John.

Checked on progress - the discs (for turning - see plans) were still not ready but will be shortly.

It looks like we dont't have shaft steel as small as required - we have
plenty at 30,50,90mm,etc. but I guess that's too big. Sorry to have got your
hopes up.

Nick
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Looks like we will have to look elsewhere, 30mm is going to be way too big and heavy...