How to make a big Stirling engine for concentrated solar

I'm often asked for details on how to make parts of the big Stirling engine that I made for powering using concentrated sunlight. So here are as many details as I could think of. This isn't intended as a blueprint, but as a guide containing lots of good Stirling engine making tips and tricks.

Big Stirling engine.
Big Stirling engine.
Powering with concentrated sunlight.
Powering the big Stirling engine with concentrated sunlight,
      specifically a big Fresnel lens.

One basic design idea was to have a big enough big cylinder, the one containing the displacer, for the solar system to focus light onto. The other was to have a big metal plate as a heat sink at the top of that cylinder for cooling purposes, one that the outdoor air could flow over for cooling purposes.

The big metal plate

As you can see below, for the big metal plate I cut up and drilled the steel cover from a microwave oven. Others have used a PC case. Ideally would be to use aluminum since it's an excellent heat conductor but you'd have to find a sheet that's thick enough to be stiff enough since everything is mounted onto it.

Top plate started as microwave oven cover.
The Stirling engine's top plates started life as the cover
      taken from a microwave oven.
Drilling holes in the plate.
Drilling holes in the Stirling engine's steel plate.

The displacer

As shown below, a big diameter can was used for housing the displacer, an apple juice can. The diameter of the displacer itself was taken from this.

The displacer is an aluminum flashing metal disk with a clylinder of steel wool wrapped and sewn onto one side.

First a metal disk is cut from aluminum flashing. In the 2nd photo below the disk is held against the bottom of the big cylinder so you can see that it's cut smaller than the cylinder, to leave a gap around it for air to flow.

Then a shaft made from a length of clothes hanger wire is bolted to the disk such that the shaft is centered on the disk.

Finally, holes are drilled all around the circumference of the disk. These holes are for sewing the steel wool on, as shown further below.

Can for the big cylinder.
The can that was used for the Stirling engine's big cylinder.
Showing the gap size.
The metal displacer held against the cylinder to show the gap size.
The attached shaft - top view.
The clothes hanger shaft attached to the displacer's disk.
The attached shaft - bottom view.
The clothes hanger shaft attached to the displacer's disk.
Drilling holes.
Drilling holes in the displacer's metal disk for sewing on
      the steel wool.

The steel wool can be found in hardware stores. If you can find stainless steel wool then that would be best since it would last longest. Below you can see it being cut with scissors and then being wrapped around the metal disk's shaft.

The steel wool.
The steel wool for the stirling engine's displacer.
Cutting the steel wool.
Cutting the steel wool for the stirling engine's displacer.
Wrapping the steel wool.
Wrapping the steel wool around the shaft for the stirling engine's

Finally, as shown below, the steel wool is fixed in place to the metal disk by sewing it on. To withstand the heat and last a long time, thin copper wire is used as the thread. The wire is tied to a hole in the circumference of the metal plate on one side, then pulled over and around the steel wool and tied to a hole on the other side.

Tying the copper wire to one side.
Tying the copper wire to one side of the metal disk for the
Pulling the wire over the steel wool.
Pulling the wire over the steel wool to the other side of the
The finished steel wool displacer.
The Stirling engine's displacer made out of steel wool.

Before the displacer can be put in place, the big can previously mentioned above that houses it has to be prepared as shown below. It's cut to a height that is taller than the displacer with around 1 centimeter or 1/2 extra height inside. This is a rough number, guessed at, using the logic that when the cylinder is in the up position the externally supplied heat will be enough to heat up the volume of air that'll be between the bottom of the displacer and the bottom of the can.

In the photos below, note the tabs cut and drilled at the open end. Matching holes are marked on the bottom of the metal plate and drilled.

The prepared displacer housing.
The prepared displacer housing for the Stirling engine.
Marking holes in the plate.
Marking displacer housing holes in the plate for the Stirling engine.
Drilling the holes.
Drilling the holes in the metal plate for the Stirling engine.

The photo below shows the top plate upside down and the displacer being inserted into the hole in the middle. The plate is sitting on books so that there's room underneath for the displacer's shaft.

Inserting the displacer.
Inserting the displacer for the Stirling engine.

A generous amount of silicone chaulking, normally used for bathtubs and sinks and found in hardware stores, is put on the open edge of the cylinder. This chaulking is rated for 300F/150C. It's then lowered down over the displacer, making sure that the displacer is not touching the interior sides, and bolted in place. Extra chaulking is then put all around.

Chaulking the edges.
Chaulking the edges of the displacer cylinder housing
      for the Stirling engine.
Bolting it in place.
Bolting the displacer housing in place for the Stirling engine.
Adding more chaulking.
Adding more chaulking around the displacer housing and metal
      plate for the Stirling engine.

Linking the rods and crankshaft together for the Stirling engine - the linkage

I linked the various rods and crankshaft together using the parts shown below. Normally they're used for the axles of model or RC aircraft and can be found in hobby stores. The rods and crankshaft are made of metal clothes hanger wire. The top has a hole through it horizontally big enough for a shaft to go and to turn freely. The bottom has a hole going up it vertically for a rod. The rod is fixed in place using a set screw. The set screw is screwed in through a hole in the side using an Allen key and presses the rod against the inside of the parts, holding the rod firmly in place.

Packaging it comes in.
The packaging the linkage parts come in for the Stirling engine.
How the holes work.
How to holes work for the linkage parts for the Stirling engine.
How the rods and shafts are connected together.
How the Stirling engine rods and shafts are connected together.
Tightening the set screw using the Allen key.
Tightening the set screw using the Allen key for connect the
      Stirling engine shaft to the rod.

The diaphragm (cold side)

A flexible diaphragm was used for the cold side. Both a rubber balloon (blue) and the material from dishwashing gloves (yellow, shown in some parts of the videos) were used and both worked. Also as shown below, the diaphragm casing was made using ABS plumbing parts from a hardware store. This could of course be made using any cylinder but the nice thing about these plumbing parts is that the rubber diaphragm is glued to a rubber o-ring that is removable and changable should it wear down, or just not work well.

Plumbing parts for diaphragm casing.
Plumbing parts were used for the casing for the Stirling engine's
Diaphragm parts - a balloon.
Parts for the Stirling engine's diaphragm.
JB-Weld to attach parts to top plate.
Using JB-Weld to attach the part to the Stirling engine's top
The parts on the top plate.
The finished parts on the top plate of the Stirling engine.

The finished big Stirling engine

The photo below shows all the finished parts in place. To see the Stirling engine in action, see the videos on the demonstration page.

Closeup of the finished parts.
Closeup of the finished parts for the Stirling_engine.
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