Recycled Detritus - How it all came together
by Dave Watkins
In general, narrow gauge design philosophy leads to simple and robust designs. I like to follow the same principles when building locomotives. Working in 16mm scale narrow gauge we are looking at prototypes which are far and away less complex than those modelled by Bob Symes. I felt that a working model ought to be much easier to design and build. Since building a live “diesel” would be in the nature of an experiment I wanted to avoid expensive materials. Many parts might need extensive modification before I had a working locomotive whilst others would prove unsuitable and have to be scrapped. Using recycled material would help keep the cost down.
Over the next week or so I made many frantic attempts to start the engine by tugging the starting cord to and fro. When my hands became too sore to carry on I built a chassis from a length of aluminium angle. The wheels were turned up from an off-cut of mild steel bar.
I had a couple of sets of gears for an off-road car lying around. I had bought them from the junk bin at a local model shop for a couple of quid. These seemed just the job for a gearbox with nice chunky teeth to transmit the power which I felt the engine ought to be able to develop. They were made from a nylon like plastic and ran very sweetly when rolled together in mesh. The gear set included pinions and large cogs plus four bevel gears which would have been part of the differential on the original car. I have no idea what car they were made for. After a few false starts I came up with a gear layout which gave a gear reduction of around 18 : 1. The bevel gears were arranged to convert the drive from the engine mounted longitudinally to a transverse direction. By using two opposed bevel gears on a sliding cross shaft a forward and reverse drive is possible controlled by a single lever acting in a visible gate like in a vintage car. To disengage the gears to start and stop the locomotive I used a simple clutch. The clutch plate came from an old wireless set, it originally had a rubber face of which more anon. The clutch is fixed to a sliding shaft which is spring loaded to bear on the end of the flywheel. Another hand lever controls the clutch. The clutch can be kept disengaged by a spring loaded trigger. Pulling the lever disengages the clutch whilst the trigger slips across to lock the lever in the disengaged position. Flicking the trigger releases the lever allowing the clutch to engage and the locomotive to move.
The final drive from the gearbox is to a jack-shaft across the rear of the locomotive. I envisaged the gearbox being in the cab with fuel tank and engine under a bonnet forming the classic two box small diesel loco shape.
At this point I could still not rely on being able to start the engine and the project looked set to fail. In desperation I had fitted an air-screw to the engine and proved that it could be started with a sharp flick. I only ever managed to start it once with flywheel and cord. Fuel consumption was voracious, the noise level in the enclosed space of the workshop unbearable and the work bench was now covered with a layer of castor oil. The fates seemed to be conspiring against me. I started to scheme out how to fit an electric motor and batteries. Then my son Peter chose to learn to play the guitar. What has this to do with railways - read on.
Saving up for an electric guitar takes quite a while when your sole income is weekly pocket money. Peter had a Traxas Nitro Hawk off-road car which needed major attention if it was ever to run again. The radio control was dead, the centrifugal clutch badly worn, the starter was bust and when running it sounded like a bag of nails. A mutually satisfactory bargain was struck and we emerged from the win-win negotiations with both parties happy. Peter could now practice riffs whilst I had to practice starting a new engine.
An Image 12 glo-plug engine is fitted in the Nitro Hawk car. I spent ages trying to work out how the 12 fitted any major dimension of the engine in metric units. I finally twigged that 12 meant 0.12 cubic inches or approximately 2 cc. The engine is air cooled and is designed to operate inside the car body- work. On top of the cylinder head a stack of cooling fins helps to disperse the heat. To get the engine running I first had to replace the broken pull start. The engine has a sort of roller clutch (called a one way bearing). This one way bearing transmits drive in one direction only so having pulled the engine over with the starter cord a spring can rewind the cord without turning the engine back the other way. A 6 mm diameter rod fitted the one way bearing. On the end of the rod I copied the arrangement used to locate the starting handle on my first car. Rather than swing a starting handle I could press the trigger on an electric drill to get the engine moving. I now felt I had an engine that might work.
Copyright Dave watkins 1996.
If you want to contact me about leisure activities Send e-mail to: dave.watkins@blueyonder.co.uk