Simple Stirling Engines

One-moving-part, test-tube Stirling engine.
Parts of the test-tube engine.
Simple Simon Stirling engine.
Parts of the Simple Simon engine.

TEST TUBE STIRLING:
  Our first Stirling was our redesign of the now-common test-tube version.
The parts are a Pyrex test tube, cloth tape, two jumbo paper clips, two #2
single-hole stoppers, glass or copper tubing, a piece of metal strap, a
corner brace, two bolts with wing nuts, three marbles, the end off of a
balloon, a base of any sort, copper-wire ball, balance-weight "washer" and
an alcohol burner.
  Cloth tape holds the paper-clip pivot axle to the top of the test tube.
The metal strap is bent and drilled 1/16" for the pivot bearings.  The
copper wire ball in the test tube acts as both heat exchanger and cushion.
The glass tubing needs to be bent using a torch, or use copper tubing.  The
big "washer" is a counterbalance.
  Adjusting: Balance it to tip counterclockwise. As the burner heats the
air, the balloon expands out, pushing on the corner brace.  This tips the
test tube clockwise. The marbles roll to the right.  The air is then forced
to the left, and gets cooled. The cool air shrinks. The balloon is now sucked
in. The test tube now tips counterclockwise. The marbles roll left. The air
is pushed right, to the hot side. The balloon expands. And so on.  It takes
a little time to adjust everything right.  The alcohol burner can be found
in hobby/craft shops (jewelry-making) or in chemistry sets.

SIMPLE SIMON:
  Simple Simon uses a displacer disk made of 5/16" foam 4" in dia. and a
balloon-and-cork piston.  The displacer cylinder is a piece of plexiglas tube
4 & 1/2" dia., 5/8" high with 3/16" wall. The piston and displacer have a 1/4"
stroke, so the crank offsets are 1/8".  They are 90 degrees apart, so when
the power piston is neutral, for instance, the displacer is all the way up
(or down).  This offset determines the direction of rotation.
  The power piston cylinder is the cap from a hairspray pump.  All the brass
wire is 3/64".  The small white bearings are Teflon 5/32" O.D., 3/64" I.D.,
1/4" long. The sheet aluminum is all .032".  The brass guide tubing for the
pushrod is 3/16" O.D., 5/32" I.D. x 1" long. The Plexiglas cylinder is caulked
to the base aluminum and caulked to the upper aluminum.  There is a tiny
roller on the end of the crank that rides in the displacer pushrod slot.
(The 1/8" offset of the crank is poorly visible.) The roller is a model-plane
wheel without the tire.
   It is important to blow up the balloon and let it deflate several times
before cutting the end off to make the power "piston" very flexible.  It is
also important to dust talcum powder (not cornstarch) on the balloon and
inside the cap and blow off excess. This engine runs faster, is more fun to
watch and more educational than the Test Tube Stirling.

The Simple Simon displacer and power piston.
The Simple Simon top aluminum pattern.

  A complete construction article about Simple Simon is in "Machinist's
Workshop" magazine, Oct./Nov. '03, published by Village Press.

SIMPLER SIMON:
SimpleR Simon Stirling engine.
  SimpleR Simon uses a flat rubber membrane instead of the balloon inside a
plastic cap, but is otherwise the same as Simple Simon. This design requires
less temperature differential.  The balloon-rubber power piston and steel
washers are rubber-cemented (not caulked) to the aluminum base.  The cork
piston is rubber-cemented to the balloon membrane.  The opening for the
balloon-rubber piston is 7/8", the wide end of the cork is 1/2".

NOTE: Common foamboard, used for signs and posters, makes a good displacer.

BEARINGS:
   There seems to be some difficulty obtaining the Teflon bearings for the
crankshaft. Another option is to use Hot Wheels type car wheels. It is
necessary to drill the rivets out and pop the car halves apart.  The axles
are 1/16" steel and the hole in the wheel is slightly larger.  Drill the
wheels out for the crankshaft that you use. The outside diameter of the
wheels is 7/16". You can make the holes in the aluminum frame that size, or
you can rubber-cement the wheels to the frame so that the holes align.
Typical Hot Wheels type car.