Piglet, a Robinson lookalike.

    Piglet was built from a set of commercial aluminium castings but bears little resemblance to the original design.  The most obvious alteration is the greatly increased length of the air chamber and displacer to both reduce heat leakage loss and to give increased surface areas for regeneration.  The firebox has been almost completely isolated from the cooler with the hot gases escaping between the firebox top and the flange, and the slim brass columns between the flange and the cooler providing an effective heat barrier.
   The air chamber/heater is made of 0.008" tinplate, as is the displacer. (and its too heavy!)  The heat baffles in the displacer are of 0.004" shim steel and are held squarely by tubes of the same material rolled to approx 3/8" diameter, (not shown in the drawing) the whole stack being held together by a light spring at the cold end. (not shown)    A new pedestal was made to accommodate ball races for the crankshaft and almost all other bearings and pivots are also fitted with ball races. 
   The cylinder is fitted with a cast iron liner, highly polished, and the lightweight cast iron piston runs in it without oil.
   Since there is no side loading on it, the silver steel displacer rod also runs without oil in a very long brass bush, extending right down inside the displacer to avoid air leakage. 
  The flywheel is by Stuart Turner. 
  The overall effect of the ball races and the oil-less piston is to give extremely low friction and, running on a 'nite-lite' candle the engine develops just over 0.6 watt, ie 25 ft/lbs/min.

  Note - The sketch is not to scale.

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