Popcan engines

So my Dad emailed me a link to a video showing a stirling engine made out of popcans. Stirling engines are pretty slick- basically operates on a temperature difference. Warm air expands, cold air contracts. One side of the engine is warm(er than the other side) and the other side is cold(er than the other side). I say it like that because theoretically, you could run one of these on ice instead of fire!

Heres a link to the instructable I followed: http://www.instructables.com/id/Build-a-Coke-Can-Stirling-Engine

Basically, you take two popcans, cut the lid off both of them and the bottom off of one of them. The one that still has the bottom on it becomes the "cylinder". It has a displacer inside made out of steel wool. Its only job is to circulate air from the top to the bottom. When the displacer is UP, there is a pocket of air at the bottom, or hot end of the engine. The air in this pocket get hot, expands, and causes the crank to spin, which drops the displacer and pushes all the hot air in the pocket up to the top or cold side of the engine. Now the pocket of air at the bottom is gone, because the displacer is in it, but it created a pocket of air at the top. That air cools, which means it shrinks, spinning the crank and moving the displacer UP, pushing the cold air back down and starting the process over.

Gads... Thats about as clear as mud. Dont take my word for it- look here: http://www.animatedengines.com/stirling.html

Pics of mine:

First attempt amid the rubble:

It didnt work. I think it was because the steel wool displacer was too loose and it didnt move the air around enough. That or my crankshaft throws were to big. Either way, I got it too hot trying to get it to work and ended up melting the bottom can.

Whoops...

Second attempt worked GREAT!

Next step was to build a base for it so I didnt have to hold it up. Even built a cooling jacket for the cold side out of a tuna fish can.

For heat, I'm using one of my popcan stoves...

Which, as it turns out, also puts out too much heat, cause I melted the bottom popcan AGAIN...

I got a lot better at makin these things... First one took me about 4 hours. Second one took about an hour, but I re-used a few parts. The "third" one took about 15 minutes to cut out a new can and transfer all the parts over.

Even have a video clip of it running! Sorry that its the wrong way and really poor quality... Gotta work with the tools I have.

Keepin busy.

Well, I made it through the first Trimester. Sure flew by- adapting my courses from a semester to a trimester was tough- we didnt get to cover nearly as much as I had hoped, but we did turn out some pretty nifty projects. New tri starts on Monday, so I will be going in tomorrow to get things ready and digest a little more turkey.

Here are a few of the projects my metals classes turned out. Keep in mind, these are 7th and 8th graders.

Lock boxes. Turned out several of these- really simple (well, relatively compared to some of the other projects) and most of them turned out great. A few "useable" and 2 or 3 "DNF'S".

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A fin for a go cart. He was quite proud of this, with good reason. It turned out great. Easily the biggest thing we've made yet with my little 24" brake and shears.

Shields. Several different designs, pretty simple project.

I even had one student make SHEET METAL HIGH HEELS. Yes, you read that right! Under construction:

And her finished product:

She designed them completely by herself.


Monday I get to start all over again from scratch with a mostly fresh batch of kids. I've been talking to a few people about the possibility of changing my schedule and doing all of the Tech classes one tri, the metals in another, and including a "new" Metals & Engines 2 class in the last tri. Thinkin it would be fun to try and build a high-mileage go cart. Dont think they do this on the High school level anymore, let alone a middle school, but it would be fun to give them the rules / regulations and see what they come up with. Anyways, hope y'all enjoyed your Thanksgiving!