Wednesday, June 20, 2012

Robinson Type Hot Air Model

Another model has just been completed and is ready to add to the display. This one is a model of a Robinson type hot air engine. It is not an exact scale model of any particular prototype, but a very close approximation.

Building it as I did, it was possible to pick and choose from various materials on hand. Construction was sort of hybrid because some parts were fabricated, machined from solid material, and some were castings.
I wanted to put lettering on the main casting, but raised letters on the side of a pattern will not lift out of the sand, so I used a method used by bell founders. The lettering was attached to a stick and after the pattern was lifted out of the mold, the stick was put down inside and gently pressed into the sand.
The results were not perfect, but satisfactory, as can be seen by the rough castings.
A couple more in process pictures. The hot cylinder was made from the end of a one pound propane tank. The displacer from a tin can. The stove was fabricated from sheet metal. There was a limited amount of head room for the burner, so I made a alcohol fired penny burner that works just beautiful as you can see in the video. The penny burner is a light weight backpacking stove for campers built out of the bottoms of a couple aluminum cans. Instructions for building one can be found on the internet
     It is an excellent running engine. I knew it would be even before firing it up, because it turned so free and easy, and yet had a little bounce from compression. Here is a short video, take a look for yourself.