LTD Stirling engine

The 1 hour LTD Stirling engine project! One problem with most Stirling engines is that they take quite a long time to build, the 1 hour Stirling engine project aims be a quick and easy LTD Stirling engine that will run off a cup of hot water. Inspired by the plans published by Soeren Scharf.

Here's the first run of my first version of this. It's not quite right yet, so I'll be building a few more to try and improve performance a little, as it only runs for about 3 minutes on a small cup of water.

The plans don't cover this design yet, but here's an alternative design that uses fishing line to connect the displacer instead of the brass rod :

YouTube Video

  • 2 Litre plastic bottle.
  • 1/16" Brass rod
  • 3/32" Brass tube
  • 1mm steel wire
  • Epoxy
  • M5 Bolt  & nut, M4 & M6 will work too
  • M5 Washers
  • Polystyrene sheet 10mm thick
  • 3 tin cans, tuna or cat food ?
  • Ball point pen
  • 3 Bottle lids
  • Thick cardboard 4-6mm thick.

  • Drill
  • Drill bit 2mm, 3mm and 5mm 
  • Tin Snips
  • Scissors
  • Vernier Caliper
  • Dremel with sanding drum
  • Spanners for bolts
  • Pliers
  • Needle nose pliers
  • Knife

[Instructions in progress!]

 Step 1: Mark, drill and cut the cat food cans

Around the side of the ins I used, there is already a line , but I've shown how to mark them in-case
your tins don't have a line. The line should be 5 - 10mm from the bottom of the can, the exact size
isn't important.:

   Fig 1a, scribe the line if needed    Fig 1b, scribe the line if needed

Now, mark the centre of the tin using a caliper or compass. Measure the diameter (Fig 2a), the caliper is set to half of this, then scribe three arcs that should meet at the centre (Fig 2b).

Fig 2a: Measure the diameter
   Fig 2b: Measure the diameter

Now you can cut the tin down to the line that you marked earlier using tin snips(Fig 3a and 3b):

  Fig 3a: Cutting the tin
  Fig 3b: Finished tins

Sand around the edges using a Dremel, this is so that it doesn't catch on the plastic cylinder (Fig 4).

Fig 4: Sanding the edges

Drill the centre hole out (Fig 5b), I used a 2mm bit, but you'll have to widen it to fit the 2.38mm (3/32) tube. It's a good idea to punch a starter hole (Fig 5a), to stop the drill slipping.

   Fig 5a: Pierce a starter hole

   Fig 5b: Drilling the bushing hole

Step 2: Cut the bushing

The bushing is made from 2.38(3/32")cut to about 15mm long using a knife. Roll the knife over the tube to cut (Fig 6a). When you've done that, slide some 1/16" rod into the bushing (Fig 6b)

   Fig 6a: Cut the bushing

  Fig 6b: Slide it onto the 1/16" rod

Grip the bushing very gently with pliers and use a 3mm drill bit into the end of the tube to remove the burrs. You might need to run the tip of the knife around the inside of the tube to remove any stubborn burrs. When the bushing is finished, slide it onto some 1/16" tubing, it must fall down the tube under it's own weight, if it doesn't, there must still be burrs.

   Fig 7a: Grip the bushing
   Fig 7b: Finished bushing

Step 3: Make the bushing jig and flywheel.

To glue the displacer bushing in place straight and true, you need a jig to hold the tube in place, in this engine, it doubles as a flywheel later, to save time.

Take some thick cardboard and draw 4 squares 7 cm square each(Fig 8a and 8b). Adjust the size to suit your tin can. Mark diagonally to find the centres (Fig 8b).

   Fig 8a: Draw the squares
   Fig 8b: Draw diagonally

Cut the squares out (Fig 9a), and pierce holes in the centres using a pin(Fig 9b).

  Fig 9a: Cut out the squares.
   Fig 9b: Pierce holes in he cardboard.

Cut a piece of 1.59mm (1/16") rod to about 80mm, and push it through the cardboard pieces.

Look at the jig from the side, if the rod looks square to the cardboard, then tape the cardboard pieces
together. You can adjust the angle of the rod by sliding the cardboard pieces sideways.

Fig 10a: Cut the brass rod to around 80 - 90mm
  Fig 10b: Fit the rod through the cardboard.
Take a ball point pen and dismantle it (Fig 11a, Fig 11b):

   Fig 11a: Dismantle a pen
   Fig 11b: Ink cartridge to be cut

Cut a piece of the ink free tube to about 2mm less than the height of the tin cans you cut earlier.
This is to hold the displacer bushing in place. Place the tube on the brass rod (Fig 12a), then put the tin can with the holes drilled in it on top of that (Fig 12b). Put the bushing on there too, making sure that it goes through the tin can:

   Fig 12a: Plastic spacer from the pen
   Fig12b: Tin can fitted to the jig

Step 4: Make the template

[Diagram for the template will be here soon]

Use the tin can to draw the curves of the template (Fig 13a). When it's done, cut it out (Fig 13b).

   Fig 13a: Marking the curves

   Fig 13b: Template cut out

Step 5: Cut the displacer cylinder plastic to size.

Take a 2 litre plastic bottle (Fig 14a), cut the top and bottom off and then cut it straight down it's length (Fig 14b). There's usually lines left from the manufacturing process that you can follow.

   Fig 14a: A 2 litre plastic bottle

   Fig 14b: Cut the ends off

Now tape your template to the cut plastic (Fig 15a), and cut around it(Fig 15b).

   Fig 15a: Tape the template down

   Fig 15b: Cut around the template

It should look like this when it's cut out (Fig 16a). You also need a small piece about 15x50mm for the seam(Fig 16b).

   Fig 16a: Cut plastic

   Fig 16b: Spacer piece

Tape the seam of the plastic together on the inside of the cylinder (Fig 17a, 17b):

When it's done, is should be a snug fit around the third tin (Fig 18):
Leave it on there for the next step.

Fig 18: Plastic cylinder fitted to the tin can

Step 6: Epoxy time!

Gather all of your parts together, here's what you need (Fig 19) :
  1. Top tin on the jig, with bushing fitted 
  2. A bottle lid
  3. Sellotape
  4. The plastic displacer cylinder
  5. The small piece of plastic for the seam

Fig 19: Parts ready for gluing

Epoxy around the displacer bushing first (Fig 20a). From this point onwards, whenever you get the epoxy out, add a bit extra to around the displacer bushing to strengthen it.

Epoxy the bottle lid next to the bushing(Fig 20b), there isn't much room, but there should be a few mm either side. Keep an eye on it as the epoxy is setting as it might  slide out of position

  Fig 20a: Epoxy around the bushing

   Fig 20b: epoxy the lid down

Epoxy the extra piece for the seam in place(Fig 20c). Tape over it to keep it in place whilst the epoxy  sets(Fig 20d)

   Fig 20c: Apply epoxy to the seam

Fig 20d: Fit the seam piece and tape over it

Step 7:  Make the diaphragm

Take two bottle caps and drill holes in the centre of each one (Fig 21a) to match the bolt size you have (M4 , 5 or 6). Then cut around the sides (Fig 21b):

   Fig 21a: Drill two bottle caps
   Fig 21b: Cut around the sides

Until you have two plastic washers that look like Fig 21c. Place one of the washers on the bolt (Fig 21d).

   Fig 21c: Finished washers
   Fig 21d: Fit one of the washers to the bolt

Take a balloon and cut the neck off (Fig 22a). Then pierce a hole through the approximate centre (Fig 22b).

   Fig 22a: Cut the neck off a balloon
   Fig 22b : Pierce a hole in the balloon

Thread the bolt and plastic washer though (Fig 22c), and stretch the balloon over a bottle cap (Fig 22d). Add the next washer and tighten it up as much as possible (Fig 22d).

   Fig 22c: Thread the bolt through the balloon

Fig 22d : Stretch the balloon out and tighten the bolt

Remove the balloon and tighten the bolt properly (Fig 22e).

   Fig 22e: Fully tighten the bolt

Continued on page 2 
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