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Bored At Work - The Good Stuff

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Walky thing

Materials:
Eraser, staples, paperclips, elastic band.

Does it work:
Mostly, yes. It'll take a few controlled steps then run out of steam. It's a fine line between over-stressing it and not winding it up enough. The front legs fall off the crank a bit easily too.

Hardest bits:
Bending the crank. It has to be done in place, because it can't be put through the eraser once it's bent. The eraser isn't very strong, and there's a good chance of ruining the axle hole.

How long to make:
Several days. I've learnt much better techniques since building this, and could make it much better now. In fact, I might just do that.

Special bits
Using a rubber as an axle housing damps the motion of the legs to a nice slow pace. They'd just spin out of control in other materials.
 
Simple compressed air engine

Materials:
Pen barrel (cylinder), pen push-button (piston), plastic sheet, paperclips, silicon tube (lucky find), company coasters (base, flywheel), balloon (cheating a little, but it's feasable you could find one after a Christmas bash), ring-bound notepad wire (valvetrain spring)

Does it work:
Nearly. If you spin the engine, it'll turn over a few times. If you spin it whilst it has an inflated balloon attached it turns over a load more times, taking sucks from the balloon each cycle. It makes power, but doesn't quite make enough to overcome its own friction. Better valve and valvetrain required!

Hardest bits:
The crank was tricky and never really ballenced. The valve leaks too much and is tricky to link up. It could have done with an air exhaust valve too, though it's so leaky it doesn't matter that much. Wasn't easy mounting the cylinder in the frame either.

How long to make:
Weeks!

Special bits
Without the valvetrain connected, the crank motion works really smoothly and sounds a lot like an engine should. By blowing into the cylinder at the right moments, you could make it run properly too.
 
4 cylinder scotch yoke engine

Materials:
Marketing material shiny cardboard, thick notepad backing card, paperclips, drinking straw (cylinders), blu-tac (filling the pistons), pen refill tube (pistons), selotape (making pistons fit better)

Does it work:
It's not really finished yet. It has no valvetrain, so won't run as such. If you prod each cylinder in turn it runs nicely though. The scotch yoke crank works a treat, and there's always a piston on its power stroke so one day it should run fine. I'm considering making a 4-way rotating valve that does both intake and exhaust in one fell swoop. Need to find the appropriate fitting parts to make it though.

Hardest bits:
The crank was a bugger to make, but came out well.

How long to make:
A few days.

Special bits
Surprisingly little friction for such a crude lump of cardboard.
 
Stirling heat engine

Materials:
Tea tin (bottom heat plate), drawing pin tin (main air chamber), pen barrel (cylinder), pen tip (piston), silicon tube (adjustable piston ring), aquarium silicon glue, Oracle demo CD (flywheel), mousemat (flywheel mounts), polystyrene packing material (displacer piston), paperclips, marketing material shiny cardboard, selotape, hot water (from vending machine), chilled water (also from vending machine)

Does it work:
No. I've come to the conclusion that air doesn't in fact expand when it gets hotter. This engine is beautifully engineered with low friction and very little leakage, and it still won't work. If you don't know how a Stirling engine is meant to work, look it up. It's fascinating. Don't try and make one though. You'll only be dissapointed when it fails.

Hardest bits:
All of it really. Gudgeon pin for the piston was especially tricky, as was sealing all the leaks and getting the piston to fit perfectly. The displacer is hand carved from polystyrene. If you've ever tried that with a good knife, you'll know it's damn hard. Now try it with a thick, blunt, crap penknife. Took ages.

How long to make:
Over a month.

Special bits
This is the first engine where I decided adjustable stuff was good. The piston is a stretchy tube forced over a cut off pen top, so it can be splayed out to the precise diameter of the cylinder. No more trying to find two pen parts that fit perfectly together. I have a primitave piston ring technology! Also, there are several folds in the linkage to the displacer. That's so it can be length adjusted so nothing binds up. Yay!
 

The early stuff | The good stuff | The latest stuff




Underwood's Axioms 1a: I don't get paid enough for this (ns)