Coffee Cup Engine

Uncle Tom’s Coffee Cup Engine

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This is a set of plans for the construction of a low temperature differential Stirling cycle engine that requires approximately 50 °F temperature difference between the top and bottom to run. A well constructed engine placed on top of an insulated cup of boiled water should run for about an hour at speeds from 300 to 50 rpm. When ambient temperature is above 80 °F, the engine will run backwards on top of a cup of ice! The engine was designed with the novice metal worker in mind, but should be a nice project for metal workers of all skill levels. It’s a good project for the home or school shop. Plans include detailed explanation of all parts and materials. Devise some simple experiments such as how the speed varies with temperature, and it’s a sure Science Fair WINNER!

cc1l_small   An engine optimized to run on ice. The top is painted black so when set in the sun while on top of a cup of ice, a greater temperature differential is achieved.

cc3l_small   Finally a use for those junk mail CD’s!!! Use them as Coffee Cup Engine flywheels!

What is a Stirling Cycle Engine?

How the engine works:

The engine operates on the very simple principle of the expansion and contraction of a gas (in this case, air) as it is heated and cooled. The displacer cylinder is a closed volume and contains the displacer (blue in the below animation) and air. When the displacer is at the top of the cylinder, the air is displaced to the bottom of the cylinder where it is in contact with the hot bottom plate. This causes the air to heat and expand. The expanding air pushes out on the diaphragm (yellow), and forces the crank pin up in the direction of rotation. When the displacer is at the bottom of the cylinder, the air is displaced to the top where it is in contact with the cooler top plate. This causes the air to cool and contract. The contracting air causes the diaphragm to be sucked in, and forces the crank pin down in the direction of rotation. This engine can be considered double acting because force is being applied to the flywheel when the diaphragm moves both in and out.

Who thought up this contraption?

The Stirling Cycle Engine was invented by Reverend Robert Stirling in 1816. It wasn’t until the early 1980’s when the first Low Temperature Differential Stirling Cycle Engines started showing up. Low temperature is considered below the boiling point of water.

To build one of these engines, you will need the following tools:

  • Sheet metal cutting tool
  • Hack saw
  • Drill press
  • Lathe (3/4″ dia. is the largest piece to turn)   If you’re creative you can do without the lathe.
  • Small hand tools like pliers, file, sand paper