Hi Gang! A few of you have been asking about Stirling
engines so I thought I'd build a single cylinder Stirling
engine and take you step-by-step through the construction.
At the end I'll show you some of the problems I ran into
and how I solved them.
To help you follow the construction, here's a little bit about this single cylinder
design. It's called a single cylinder design
because there's just one outer cylinder that contains the working fluid,
which is air in this case.
The air inside it gets heated down here.
This other cylinder is a solid mass that moves up and down.
When it moves down, it displaces the hot air at the bottom,
forcing it to move to the top. So this cylinder is called a displacer cylinder,
or just a displacer.
The displacer moves up and down under the driving force of this flywheel.
As the flywheel turns it repeatedly lifts and lowers the displacer.
In this case the connection between the flywheel and the displacer is this crankshaft
and this thread. Since it is a thread, gravity does some of
the lowering too.
The other main part is this flexible diaphragm, which in some designs is a piston.
In this case it's just a balloon that's connected to the crankshaft using
these two connecting rods.
It looks like the flywheel lifts up the diaphragm but it's just the opposite.
Hot air expands, and even though most of the hot air is at
the bottom at this time, the overall volume occupied by the air is
increasing. It's that increasing volume of air that inflates
the diaphragm and pushes up on the connecting rods.
That turns the crankshaft and adds energy to the flywheel.
That's what keeps the flywheel turning and makes this whole thing work.
When does the air cool down again? It cools down while it's in the top part of
the cylinder. When the displacer comes back up,
it forces the cool air back to the bottom so that the whole cycle can repeat again.
Now let's go step-by-step through the construction.
I'll start with the single cylinder, which in this case is a can.
The can is a tomato paste can and it is about 5 centimeters wide by 8 1/2
centimeters high.
Next is the wooden frame that holds it all together.
And it works like this. The can goes in here,
and then this piece of wood right here is a tight fit,
wedged in there like that, and that holds the can in place.
The only really important dimension here is the distance from the bottom of the can
to this hole here. There's one hole right there, drilled,
and another one on the other side and they're lined up.
And that distance from the bottom of the can to that hole is 16 centimeters.
The displacer cylinder needs to fit inside this can,
but air needs to flow all around it. So the can is 5 centimeters in diameter.
I'll make the displacer cylinder 4.5 centimeters in diameter.
The height should be about 6 centimeters. I have this piece of balsa wood here,
and I'm just going to create enough layers of this
to build up as close to 6 centimeters as I can get.
This is the coat hanger wire I used for the crankshaft.
And it's a fairly flimsy one. I usually hate them as coat hangers.
This is another coat hanger wire and it's much stiffer,
so I'm not going to use that. That's probably going to be hard to shape.
The actual cranking part is only about 11 centimeters,
and I could have about 10 centimeters sticking out each side,
so that's around 31 centimeters. Around a foot basically, or 30 centimeters.
And this central portion of the coat hanger is actually around 30 centimeters.
As you'll see, these aren't the crankshaft dimensions I started
out with, but they are what worked in the end.
And there's the finished crankshaft.
For the connecting rods, I'll use this piece of 5 millimeter square
balsa wood. And I'll cut two pieces 8 centimeters long,
each. And 1 centimeter from the end of each one,
I'll put a small hole for the crankshaft. I picked a drill bit what was a fair bit larger
than the crankshaft. That's so that this can easily be put on at
any time, or taken off at any time.
Next, I need to take this paperclip and make a little loop that can hang down
from this middle piece right here, and that can swing around it freely.
And the displacer cylinder will hang from that.
Here's the end result. Hopefully that'll work.
Okay, I've taken it apart so I can assemble it, with the shaft.
It seems to work fairly well.
I'll use this balloon for the diaphragm. I just need to cut it.
I can always trim it more later so I'll cut it fairly long.
Next I want to attach a thread to the displacer cylinder.
So I'm going to push this nail into the displacer cylinder.
And I'll make the thread for now... about a foot long should do.
Next I'll mark where I think the very top center of the balloon is.
I've threaded a needle onto the thread, from the displacer cylinder.
I'm just going to push that needle up through that mark.
The connecting rods also have to be attached to the top of the diaphragm,
because it's the expanding diaphragm that pushes the rods up.
So I'm going to take 2 thumb tacks, and just from inside the balloon,
I'll push them up through, about a centimeter or so away from
the thread that I just pushed through, on either side of the thread.
I'm not quite ready to put on the connecting rods yet.
The next thing I need to do is stiffen the diaphragm a bit.
And to do that I've cut these 4 little pieces of cardboard
each one about 1/2 a centimeter wide by 1 1/2 centimeters tall.
And I'm going to glue them in a cross pattern on top of the diaphragm, just to give it some
stiffness.
Next, to connect what I have so far. First to attach the connecting rods,
using the thumb tacks. I'm going to put on the rubber band at this
point, to give it a good air seal there,
although it looks pretty good anyway.
Okay, so next to tie the thread in place. And it goes through the paper clip that's
hanging down here. The way you want it is when the paper clip
is at its lowest, the displacer cylinder is at its lowest.
That way, as the paper clip rises, the displacer also rises.
And when the paper clip's at the top, then the displacer's at the top.
Here's the flywheel. It's just an old piece of wood that I had.
I made a hole in the middle that was the right size for the shaft,
stuck the shaft through, bent the shaft,
and then put 2 staples, just to hold it in place.
And that works fine.
And lastly, some tips.
This wasn't the first crankshaft I made. In fact, it was the 4th.
I started out with this big one right here, and gradually shrank and shrank and shrank,
until I was satisfied with this piece. But these two pieces still had to shrink.
And the reason is, because of the lengths of the connecting rods,
the balloon was having too much trouble moving them through the
distance that they have to travel.
As you saw, I initially just push the thumb tacks up
into the connecting rods, but I later went back and added hot glue to
make them hold on better.
Well, thanks for watching!
Check out my youtube channel, rimstarorg for more videos like this.
As well as other Stirling engine videos, there's one on how to make a van de graaff
generator. One on how a crystal radio works.
And another about a fresnel lens taken from a rear projection TV.
And don't forget to subscribe if you like these videos,
or give a thumbs up or leave a question or comment below.
See you soon!