D uring early 2008 I was searching for my next project and while at the Stirling Association Exhibition at Kew found a subject that I felt would be both challenging and hopefully satisfying. Julian Woods of Stirling Stirling had made a very attractive 1890s Benz look-alike radio controlled 3-wheeler car, powered by a ‘beta’ Stirling engine.
(at this stage I had no idea how a Stirling engine worked, let alone what ‘beta’ meant). Fortunately Julian was very helpful, and together with one of his excellent books, many photographs of his car and some sketches and notes he sent later, I was on my way.
The project started with an understanding of Stirling engines, their operation and manufacturing requirements, after which general arrangement drawings were produced to establish how the main components related to each
other, their overall size and their position in the assembly of the car. After a lot of juggling (I still use a drawing board), the pieces began to fall into place.
At this stage I decided to break the project down into five distinct areas: engine, chassis, transmission, wheels and the rest.
The engine called for some interesting machining, such as turning a 1in. diameter stainless steel bar into a cylinder having a wall and blind end thickness of 0.010in. for the displacement cylinder and piston. Having been told that air leakage is a definite no-no, my somewhat limited engineering skills were also tested to the limit when producing the cast iron power cylinder and piston.
The final major consideration in making a Stirling engine is minimizing friction, since these are relatively low efficiency machines, exacerbated when driving something heavy like a model car. Power for the ‘hot end’ of the engine is produced by a gas fired ring burner requiring careful tuning to obtain a perfect
flame. Amazingly the engine performed perfectly on its first test, spinning at approximately 1000 rpm, thus giving me confidence to move onto the next stage.
The chassis, by comparison, was fairly straight forward, requiring a bit of steel tube bending and brazing, together with the machining of a few pieces of aluminium.
The transmission on the other hand was a little more complicated, necessitating gear cutting and the modification of a model car differential unit to control the large diameter rear wheels. Neutral, forward, reverse and speed control are achieved by moving the first drive shaft, which is in friction contact with the engine, laterally either way from a central neutral position.
Constructing the wheels was most satisfying. The large rear wheel rims were
made from brass tube, formed into a circle, brazed and then machined to remove 50 per cent of the tube, to create the rim. The front rim was a relatively straight forward operation being machined from aluminium, as were all of the hubs. Final assembly of the wheels was achieved by the use of jigs and dentist’s stainless steel wire for the spokes. O-ring
