Jackrabbit On It's Way                                                                                                    

Insides of a piston.

Good news: I have pistons that work well. After several variations, I found that  the inside of PVC pipe is smoother than ABS pipe. The finished cylinders are about 16 inches long with an 11” stroke and a 4” inside diameter. The lubricated o-ring slides easily in the PVC cylinder. I can rapidly stop the flywheel from turning by putting a finger over the air inlet tube during both the compression or the vacuum phase of the stroke. I do not feel any air leaks.

Dual pistons 90 degrees out of phase.

The flywheel is also finished. I scavenged a discarded bicycle from Isla Vista after the students moved out for the summer. I mounted the cut-off back half of the bike, upside-down on a board so the crank can turn the tire freely. I removed the gear shifters, shortened the chain, welded the rear sprocket to the rear wheel (crank and wheel always move together now) and welded one of the crank pedals at a 90 degree angle (instead of the normal 180 pedal configuration). The pistons pivot on a 3/8” steel rod welded across where the seat post would have gone.

I gave up on making PVC over-pressure and under-pressure relief valves. I just could not make a ball valve that would not leak a little air. I tried plastic balls and stainless steel balls to no avail. Instead I will use small electric air valves. If the controller senses pressures that are too high or too low, then it will open a valve to vent to the outside.

Jackrabbit layout of components.

Next, I have to locate containers to make into displacer vessels. There are definitely going to be two Stirling engines connected to one flywheel. My calculations predict the finished engine should produce about five foot-pounds of torque for a 60C temperature gradient. I will be happy if the engine can just sustain the turning of the flywheel. The Jackrabbit is off to a good start.