Tips and Tricks

While building our engine thus far we have not followed the instructions exactly as they are written. We have come up with some helpful nuances that could aid others this year, as well as future students, in building their engines. I would like to open up this post as a sort of running dialogue for the new ideas we come up with.

So far we have made some adjustments:

- Instead of worrying about the exact center for the pressure vessel top and displacer top, guesstimate on one. What really matters, and why the instructions seem to call for "exact center" is so the two line up. But if you put a hole in one first and then use that hole to line up your next hole, you have the two lined up for a guaranteed match so as to avoid friction.

- The needles are hard to bend, so JB weld your needle inside the bottom of the displacer top with the eye of the needle underneath but with the whole needle vertical. The width of this is greater than the rest of the needle so it shouldn't puncture through all the way and the JB weld shouldn't break.

- Drilling and welding both the crankshaft support and the pressure vessel to the elbow joint increases the space for a leak and error. If you cut one of the crankshaft supports shorter you can mount it above the elbow joint and then you only have to worry about sealing it to one surface.

Feel free to point out any flaws with these adjustments. I just see this as a running list of ideas that we can bounce off of one another. Let me know your thoughts.

Third Entry: Final Preparations

Over the past few weeks Mike and I have worked diligently on our engine. We have spent every lunch period in the physics lab for the past week and a half finishing all the prep work for our engine and at last we are ready to assemble. This coming Monday we will begin assembling all the pieces of our engine so we can test it soon.

I have included some photos, as well as a short video clip of a basic test of our engine's pressure vessel construction.

Displacer:
We put a needle through the exact center of our displacer top and JB welded it in place. We then
JB welded the displacer top onto the displacer bottom. We attempted to weld it from the inside, but some of the epoxy was squeezed over the edge and ended up on the outside of our displacer. To eliminate this and thus minimize friction, we sanded
the edges of the bond until
the glue became flush with the surface of the can itself. We also checked for any tiny gaps, resealed them with JB Weld, and sanded again.




Pressure Vessel Top:

Our pressure vessel top will be what seals off the engine. We first put a whole in the center of our vessel top. We realized that more important than being the exact center, the pressure vessel top simply needs to be centered on the displacer to minimize friction. Thus, we used our displacer top to line up and punch the hole. Next, to make it air tight, we used a small washer and a small square of tin to create an air tight chamber around the whole in our pressure vessel top. Next we punched another whole through the tin part of the chamber. This creates a tighter seal that prevents air from escaping our engine. However, we also had to work the needle to slightly widen the hole so that there would be no friction when the displacer pin slid through the pressure vessel top. We attached all these parts using an RTV gasket sealant.


Crank shaft:

The crankshaft is what translates the lateral motion of the displacer into the angular motion of the flywheel. The width of it's bends are extremely important because they dictate the range of motion of the displacer. Therefore, it must be very precise if we want out engine to work. Note though: the angle of the individual bends is not extremely significant, what matters is that the widths of the bends are correct, and that the two bends are exactly 90 degrees out of phase.




Crank shaft supports:


These are simply attached to the pressure vessel to hold the crankshaft in place. Notice that instead of following the instructions and making two equal length supports, we cut one shorter so that we would not have to drill a whole and both attach our elbow joint to the support and the support to the pressure vessel. This decreases the odds of a leak.




Elbow Joint:

The PVC elbow joint with a balloon will inflate as hot air rises. The balloon is then attached to the crankshaft, causing it to rotate the flywheel.










A quick video of how it all works:

This video demonstrates simply the lateral motion of the displacer in our pressure vessel to test how well it will work. We saw that friction really is not much of an issue.

Second Entry: Parts

We are about a week into the project so far and we are just finishing up making our basic parts before we begin assembly. As of now we have a ring stand attached to the bottom of our pressure vessel. This will eventually be attached to a wooden block, because if it is not mounted we fear that the movement of the legs (i.e. the ring stand) would cause the system to loose too much energy. Next, we have a bottom and a top to our displacer. Finally, we have a top to our pressure vessel. Here are some pictures with brief explanations:

1) Ring Stand and Pressure Vessel Bottom:

The three legs of the ring stand support the pressure vessel. If they are bent and then nailed down, we can bring the engine closer to the flame (increase the heat in) and minimize any energy lost from the engine shaking. The pressure vessel bottom is essentially the case for the engine. It contains the air which will move to do work, as well as the displacer necessary to assist in that work.

2) Displacer Top and Bottom:


The displacer has two parts, a top and bottom, that will eventually seal together to create one hollow, airtight object. The displacer serves two functions. First, it controls the air flow from the hot and cold sources by narrowing the gap through which the air can pass and essentially dividing the engine into hot and cold compartments. Secondly, as the displacer moves up and down due to the motion of the hot and cold air, an attached needle (yet to be displayed) will be attached to the crankshaft.

Although we have not attached the top and bottom yet, here are some pictures of the top portion resting on the bottom portion. Notice how the diameters are nearly equal and the fit is very tight.









We want to be sure that the displacer creates minimal friction with surrounding components and moves properly (i.e. up and down at the right heights), so we cut the displacer's height as accurately as possible. Then once we attach the displacer top from the inside, we are going to sand all the edges down so that the rim of the displacer top is flush with the rim of the displacer bottom.

3) Pressure Vessel Top:














The pressure vessel top simply seals off the entire engine so that no air can get in or out of the chamber. It also will contain a hole through which the needle will pass and attach to the crankshaft. Mostly though, the top simply keeps the number of air molecules at a relatively constant level.

That is all we have for now. Stay tuned and we will have some more pictures up, including the final versions of the displacer top and pressure vessel top, as well as the crankshaft and crankshaft supports.

Thanks,

Keith Berquist
Mike Reher

First Entry

This blog has been created to track our progress in the process of building a working sterling engine from scratch using basic materials. It will be an interesting and difficult endeavor, and we hope you enjoy following us through the process. We will have another entry up in the next few days with pictures of all our unassembled components.

Thanks,

Keith Berquist and Mike Reher