Description
Not all the details of the carriage are known but the drawings which accompanied the original patent have survived, as have contemporary drawings made by a naval engineer who was sent to examine it. Further information has also been obtained from eyewitness accounts.
The carriage had 8-ft-diameter driving wheels which were intended to smooth out the road surfaces of the time, to help the fire from being extinguished by shaking. A forked piston rod reduced the distance between the single cylinder and the crankshaft and was considered a singular innovation at the time. Spring-operated valve gear was used to minimise the weight of the flywheel, overcoming one of the drawbacks of industrial steam engines.
The engine had a single horizontal cylinder which, along with the boiler and firebox, was placed behind the rear axle. The motion of the piston was transmitted to a separate crankshaft via the forked piston rod. The crankshaft drove the axle of the driving wheel (which was fitted with a flywheel) via a spur gear. The steam cocks (used to blow out water condensate from the steam chest), the force pump and the firebox bellows were also driven by the crankshaft.
The patent shows two features which may have been incorporated by Trevithick to discourage unlicensed copies: if the engine had been assembled as per the patent drawings it would have been able to run only backwards; and if the water pump had been arranged to be driven by the valve spring as shown, it would have run unevenly if at all.
It is reported that the coach builder William Felton charged £207 for building the coach (not including the engine) and that the cost of transporting the engine from Falmouth to London was £20 14s 11d. The cost of the engine is unknown.
Read more about this topic: London Steam Carriage
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