Campbell's Ouany demonstrates that ifs even possible to build large scales in small spaces. The model measures 5ft 6in by 2ft bin but packs in enough operation to entertain visitors at exhibitions. Fundamental to the design is a pair of working excavators - a Ruston-Bucyrus dragline and Ruston•Bucyrus Crowd Shovel. Both work in the same way as their prototypes dating from an era before hydraulic power, they fascinate viewers with their collection or ropes and pulleys all skilfully operated to scoop sand to load the skip wagon trains. The red and cream dragline was the first excavator model built by John Campbell. Modelled with the post•1954 cab, the model is electrically powered and plugs into the baseboard with an umbilical cable. Constructed as a removable unit for both transport and maintenance inside the body is a complicated construction housing all the motors and gearing. This allows the machine to perform all the actions of the prototype apart from driving itself around the site. M those ropes and pulleys must run smoothly and reliably too. The layout operates continuously at shows scooping many scale tons of sand so temperamental machinery cannot be tolerated. With the dragline built, the design of the layout was worked out around it. If you have a working dragline, you want to dig something and tip it into skip wagons. These need to go somewhere to be unloaded and that somewhere needs to be high enough for the load to fall out into a pile. This means the design has to incorporate an incline to raise the track bed up a few inches. Loaded wagons hauled around tight curves on less than perfectly laid track work is the territory of the narrow gauge industrial diesel and in 16mm scale, there are plenty of kits available. Unfortunately. these normally only drive a single axle so don't provide enough traction for the job, so John scratch-built all his models only using kit parts where they were appropriate and made the job easier. His formula used for all the models includes worm and wheel enclosed gearboxes driven by can motors and Debin chainsets to make each model four-wheel drive. This isn't a problem: all the locos carry their own power in the form of MA rechargeable batteries. With four locos to choose from and only one required at a time for operation, the others can be on charge. As well as spreading the wear, this ensures viewers who return to the model during the day see a different engine in use.
M operation is 'hands-off with points being changed by a 'wire in tube" system - actually camera shutter release cables. Before these, servo motors did the job, but their gears didn't like coming into contact with the sand. Unloading the wagon is achieved using another cable. this one designed to work the choke for an MG Metro car to for tipping. The skip body is righted by a length of wire as the train passes by. Both diggers are operated with nothing more complicated than a series of double-pole double-throw switches. Simple that is. until you realise that at least two switches need to be operated at the same time for some movements. Once you've filled the dragline bucket. it has to be raised up but if you don't let out the line used to pull the scoop towards the digger, the bucket tips forward. emptying it again. Novice drivers can spend a lot of time dumping sand where they don't want it. The experienced team makes it all look so easy.
