The Terrapin: Linkages, Regenerator Cam and Timing.                        

Vector sum of force (red) applied to a linkage.

I am at the end of the construction phase; I have finished making the linkages between the active components of the engine.  A linkage is a straight rod of metal or of wood that has pivot points at it's ends. For a linkage that is free to rotate about pivot points, force is transmitted longitudinally along the  the major axis; hence the rod does not need to be very thick. Some are made from ¼” square aluminum bar and some are made out of ½” wooden dowels.

For pivot points that rock back-and-forth, I pressed brass bushings into holes drilled in the active component with ¼ inch steal bolts as pivots. On the end of the rotating power crank shaft, I pressed a skate ball bearing into a 7/8” hole drilled into some 1/4'” aluminum stock that I had.

Regenerator cam and power piston crank.

The regenerator cam is an offset 8” aluminum disk that rotates inside a box made out of sandwiched sheets of acrylic and plywood. There are four screen-door rollers in the box that hold the disk at the edges. The net effect is that the box moves back-and-forth six inches, each time the flywheel rotates once.

Regenerator linkage.

The passive cable linkage to the regenerator did not work out. One edge of the regenerator would occasionally hang on it’s gravity fall on the way down. I changed the linkage system back to the original active push/pull rod system. The regenerator cam now rocks two wheel segments back and forth. The wheel segments drive vertical dowels that actively lift-up and actively push-down the regenerator. A 374 gram counter-weight is attached to the flywheel at 13 inches from the hub, for regenerator balance.

Timing pointer on flywheel.

I welded some steel stock to a 1” long nut to make a timing pointer that can be very firmly attached to the inner threaded axel that emerges from the flywheel face (the power piston output). The other end of the pointer has a peg that fits into a hole in the face of the flywheel for the desired timing position. A ninety degree phase angle between the power piston and the regenerator positions is nominal, but I will be playing with that. The pointer also acts as a flywheel counter-weight for the power piston system.

As I turn the, now finished, engine’s flywheel by hand, I can hear the hissing of many air leaks coming from the vessel. Indeed, if I blow liters of air in though the vessel’s vent tube, it leaks out before the piston has a chance to move. I have almost total loss of compression. I will have to disassemble the vessel and patch air leaks before trying out the engine.