Servo Controlled Target Trolley
In 1939, H. E. R. Coward identified that the initial method of setting the trolleys in motion meant weather, trolley & rail conditions can affect how the trolley behaves once set in motion.
To remedy this, H. E. R. Coward designed a Servo Assisted Control Mechanism and submitted a report in August 1939 to his bosses at the Royal Engineers War Department, detailing the changes and subsequent operation of the trolleys.
The following diagram produced by Mr Coward accompanies the description of the mechanism.
 |
 |
Mr Coward described the mechanism thus:
"The servo brake consists of a cylinder approximately 4 inches in diameter, closed at one end and containing a piston which is coupled to the trailing brake arm of the truck by an intermediate lever. The closed end of the cylinder is connected by a 3/8th inch diameter tube to the brake valve by means of which it can be connected to the induction pipe of the engine.
The standard centrifugal govenor, supplied by the engine-makers Messers J. A. Prestwich, was selected for the control and has proved to be very satisfactory.
And driven by a length of 1/2 inch piton cycle chain from a sprocket spigoted and spot welded to the boss of the coupling on the driven shaft on the outputside of the fluid flywheel. thedriving and driven sprockets selected are 16 and 14 teeth respectively.
The control arm of the govenor was modified from the original to give a suitable angle for coupling to the carburettor throttle.
The control arm is coupled to the carburettor throttle by means of the rod N, the piston of the servo brake valve and the link A - refer to accompanying original diagram parts 1 & 2."
Target Trolley Servo & Braking control close-ups - Andrew Coward collection
The full report, from Mr Coward, is reproduced below giving further details of the mechanism and of the operation of the truck (as he refers to it).
Next chapter:
Return to start: