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Hey, my name is Bryan Frobb, 15 and in grade 9. I have been working
hard on a sciencefail project with Stirling engines for many
months. I have the MM1 coffee cup engine and have read "Around the
World by Stirling Engine". I tried building a very difficult model,
but failed miserably, so I have decided that, with the few weeks
left before science fair, I will have to settle on a test tube
engine. I have very very limited materials, and have not been able
to build a working model. I have tried making several models, but
am lacking materials such as glass syringes. I am working on a
model that uses a balloon instead, but I don't think I quit
understand the concept on which it runs. Perhaps if I did I would
have a fighting chance at building a better model.

Here is a link to an mpeg of a working test tube engine. It seems
completely backwards to me, I am not sure I understand why the
marbles roll to the left. Any help you can offer me would be
greatly appreciated.

http://www.nmri.go.jp/eng/khirata/stirl ... sttube.mpg

Bryan

It is confusing, isn't it? Do you understand the operation of the Coffee Cup S.E.? The marbles act as the displacer. With the marbles near the top of the tube the bottom of the tube heats the air, which expands pushing the piston (balloon, syringe, or other actuator to push the top of t.t up, causing marbles to roll to bottom of tt and forcing the air to the cooler end or top of the tt where it cools and relaxes the actuator, tube tips back causing marbles to roll to top again so that the air is heated agian and cycl repeats. Two problems: 1. Usual design does not restrict the amount of tilt which must be limited by "stops" to limit movement. 2. The 'balance' point must be adjustable so that the right point can be located. A bit of steel wool or fiberglass in the bottom of the tube works as a stop.
A simple design in "Adobe" PDF file is located at URL: http://www.mech.canterbury.ac.nz/resear ... estube.pdf