The Terrapin: Frame, Power Beam, Cranks, Flywheel and Timing
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| Balsa-wood 1/10th scale model |
I have simplified the stirling engine design somewhat after making a 1/10th scale model to see if any of the moving parts were going to bump into each other. They don’t, but I decided to lift the regenerator with cables and let gravity take it back down rather than the earlier and more active push-rod-connected-to-wheel design. I’m hoping the regenerator will not jam on it’s way down.
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| Engine frame. |
I built the frame for the engine out of five 2x4s and a quarter sheet of ¼ inch pressed wood. It has a 2’ x 3’ footprint and stands 4’ 3” tall.
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| Power beam |
I welded several pieces of ¼” steel bar to make the power beam. Force from the power piston is transferred to the power beam along an 11 inch curved brass track that allows the piston stroke length to be adjusted from 0.1 inch to 1.5 inches in 13 increments. There is a locking handle that holds each notched increment in place. The beam space between the brass track and the surrounding welded steel is filled in with epoxy resin. The reason the track is curved is so that each power beam position remains centered with respect to the flywheel and the power piston. If the power beam is held in it’s horizontal position (Crank 90° from TDC) then the piston is at it’s mid position regardless of the power increment setting.
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| Welded parts |
I welded some 5/8” all-thread, ¼” iron pipe and some 1/8” steel bar to make the dual concentric crankshaft. There is a internal threaded crankshaft (offset 1.125”) that harvests energy from the power beam and an externally concentric crankshaft (offset 3.125”) that will drive the regenerator motion. The external shaft is fixed to the 3’ flywheel and the internal shaft passes out of the front of the flywheel where it can be attached to the flywheel at chosen angles, thus determining the timing between the two cranks. For any chosen timing angle, both shafts are fixed together and rotate at the same speed.
