For the mathematically inclined, I have included 3 pages on the design of the TTR. Click here to take a look.

Our first public exposure was at the PRIME exhibition in September. We can't truthfully say that TTR was the hit of the show (a low temperature differential engine took the best of show award in the Stirling category) but we did generate a lot of interest, particularly from the more knowledgable model engineers at the show. We show below some photos and commentary regarding the building of this engine. Click on the thumbnails below for a larger view:

Here is the gear/rhombus link assembly in the test mode - the displacer shaft is a dummy one used to get the setup correct for timing and fit. In the large view you can see the ball bearings in the links. the gear shafts are also running in ball bearings for minimizing friction, the number one enemy of small scale Stirling Engines.

Here are the component parts of the rhombus before assembly: .

Here is the cylinder in the process of being lapped to size and parallelism, another critical factor in making a successful Stirling model. Any binding of the piston because of out of roundness in either the piston or cylinder is fatal. Dr. Senft, in Live Steam magazine (October, 1979,pp. 26-29) wrote on cylinder lapping. The lap you see here was made in my shop, and is used with "Timesaver" non-embedding lapping compounds.
 

Here you see the parts that will go together to make TTR. The upper unit, including gears and rhombus, the finned cylinder, the test tube (which will be shortened to match the length of the cigar tube), and the cigar tube displacer. The displacer is closed with a turned aluminum plug that is a snug fit in the tube. It will be Loctite'd together with the displacer rod when the engine is assembled.

The test tube is fitted to the cylinder with an o-ring seal, backed up by an aluminum spacer ring. On final assembly, I found that a single o-ring was not enough to hold the test tube accurately aligned, so a second o-ring was put in place to make that alignment. In the design phase of this project, we questioned whether or not the o-ring would overheat in operation. At PRIME the engine ran for more than 30 minutes at a time, and repeatedly during the day. At no time did the test tube get too hot to touch near the power cylinder, so O-ring failure should not be a problem. I estimate the total running time on the engine is now (Oct. 9)over 30 hours, and it just keeps getting better!

The power piston assembly is shown here in two views. It was turned from graphite, with a central hole reamed to a close fit on the displacer rod. The two piston rods coupling the piston to the lower rhombus link are 1/16" drill rod, threaded 0-80 on both ends. The top end screws into the rhombus link, and two 1/8" brass "nuts" are screwed on the bottom ends, and recessed into the piston. This was done because the clearance between the power cylinder and the displacer is very small in a rhombic engine (about .050"). If you look closely in the larger view, you will see 1/8" brass collars at the top end of the piston. These were Loctite'd in place at assembly.
 
 







This view is our first trial assembly, where we establish the length of the displacer piston rod to provide proper clearance between the power piston and the displacer.














Here, we have the Plexiglas base fabricated, and are beginning final assembly:
 
 

More progress here. 

Final assembly was completed the evening of August 17, 1998. A successful run of about 5 minutes was completed that evening, and another the next morning. Wednesday, August 19, we had at least 6 runs of over 15 minutes each, and one af over 30 minutes, so TTR has proved itself a fine running machine. Here are some still and action photos taken during and after these runs.
 

TTR at rest	...and in action
from the business end	...and a little closer

After the above photos were taken, we made one more modification of the engine, replacing the large flywheel with two smaller ones. We were getting a bit of rod knock (as best we could tell) and thought a fully symmetrical layout would correct that. It did improve, and the modification improved the esthetics of the engine, too - or at least we think so. The following photos show the new arrangement:
 

	We rather like our magic lamp, so we decided to inflict a photo of it on you, too!

It is hard to describe the feeling when an engine you have designed and worked for many hours finally runs. I usually just stand there in awe, amazed that such a collection of parts has finally come together, and actually WORKS! For those of you who have built Stirling Engines from plans or kits, I urge you to strike out on your own and design your dream engine. You can collect dimensions from successful engines, and design yours with similar characteristics, but with your own unique features. And it will run! It's a great feeling - one not to be missed in this great hobby. Happy Stirling'n to you all!

Roy
 
 



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