Mrs Domieo


There are two versions of Murray’s 1802 Hypocycloidal Steam Engine available to model engineers. Anthony Mount’s version is available from Polly Model Engineering, and this version shown by Mrs Domieo at Bristol in 2019  is from Cotswold Heritage.

Murray’s engine was one of a number of designs produced after Boulton & Watt patents expired. It could be classified as a portable engine, in that it was self-contained it could be erected anywhere.

The hypocycloidal motion, whereby reciprocating motion was transformed into rotary motion, was unique. The geometry of it is that a point on a circle rolled around the inside of another circle of twice the diameter will scribe a straight line. In practice the small circle is a spur gear which rolls around inside a ring gear with internal teeth. As the piston rod rises and falls, the end is pivoted on a pin fixed on the periphery of the small gear. The small gear rolls around and, through a crank, drags the crankshaft round.

Bob Middleton has produced a design for a model horizontal hypocycloidal engine.