Monday, 17 February 2020

Nice Butt

This weekend I had to learn all about rainwater collection systems. You might have seen big green water butts standing innocently next to guttering downpipes. What I didn't know is that they're evil, and that they're biding their time until they try to knock your house down. I assumed that the guttering downpipe fed into the butt, and that it then had an overflow that fed into a second butt, or back into the guttering. I was wrong. The "diverter" that you let into the downpipe has a weir in it, and an airtight pipe to the water butt. Water can either flow into the butt, or over the weir and down the rest of the downpipe. There are a couple of reasons why this system is better than mine. The pipe to the downpipe can be small and flexible, if the flow down the downpipe overwhelms the capacity of the flexible hose, then the rest of the water just goes over the weir and down the rest of the downpipe.

It's a great system when everything is new. Now imagine that this water butt (which weighs 160kg when it's full) has been out in the garden for a few years and has been subject to hundreds of hour of UV degradation and dozens of frosts. Either the crappy plastic stand breaks and you don't replace it with something exactly the right height, or the flexible hose perishes. If the butt has been lowered by more than a few mm then the top of the butt is below the weir and all the rainwater flows down the side of the butt. If the flexible hose has perished the same thing happens. You are now collecting all the rain off your whole roof and funnelling it into one corner of your patio to try to undermine the foundations of your house.

I suspect that there's a better system where all the rainfall for an entire town is gathered together. It could be filtered and treated on an industrial scale until it's drinkable and doesn't bread lava and bacteria and then it could be piped back to individual households who use as much or little as they see fit - no matter how much or little rainwater their roof collects... Oh wait...

Richard "mains water" B

Tuesday, 11 February 2020

MOT

Last week my sports car failed its MOT. The fault was "Excessive play in rear suspension linkage. Look I can move this with my hand. This one isn't even done up Richard." I was told to take it home and re-torque all the fasteners in the rear suspension before I re-presented it. The rear suspension on a Caterham like mine is quite interesting and quite simple. There's a strong horizontal tube that has the wheels on it. It doesn't have the differential in it to save weight. The tube is kept in the middle of the car by a triangular A frame that is bolted to the middle of the tube and to the chassis well in front of the wheels. To stop the tube from moving forwards and backwards there are a pair of "radius arms" that are bolted to the ends of the tube, and to the chassis well in front of the wheels (like the swing arm on a motorbike). If I was richer the for/aft position of the tube would be maintained by 3 part Watts linkages giving almost perfect vertical travel.

What was interesting is that only the radius arms had loose fasteners, and it's only the radius arms that you have to take the seats out and get inside the car to work on them. Coincidence? Or something less? I wonder whether Caterham forgot to nip them up when they changed the differential.

Richard "anti-sabotage lacquer" B

Wednesday, 5 February 2020

Verb

Last week I witnessed the birth of a wonderful new verb. One of my colleagues had borrowed his girlfriend's car to get to work. When he bought a new car he had to drive his girlfriend's car home and then get his dad to pick him up and take him to his new car so that he could then use that to give his girlfriend a lift home so that eventually she would be re-united with her car and he would be in the same place as his new car. He said "I'm off to towers of Hanoi my new car".  Most of my readers are computer programmers so you're probably already thinking how perfect it is. If you're not familiar with it, the Towers of Hanoi is a little puzzle with three pegs and a stack of different sized disks. You have to move the stack of disks from one peg to another. The rules are that you move one disk at a time, and that you can never put a bigger disk on top of a smaller one.

Computer programmers have almost always studied it because it's a beautiful example of recursion. The recursive solution is:
1) Move all but the biggest disk onto the spare peg. 2) Move the biggest disk to the destination peg. 3) Put the rest of the stack on top of it.
In step 1 and 3 How do you move the "rest of the stack" – you're only allowed to move one disk at a time? Just follow steps 1) 2) and 3)

Yesterday a friend drove from his house to an MOT station so that he could pick ne up there and take me home, leaving my boring car at the MOT station. This morning, after pushing my scooter out of its way I drove my sports car to the MOT station so that I could leave it there and get in my boring car to get to work.

Richard "Bring on the self-driving cars" B