Animate a JCB
Graham Goodchild creates a working cameo scene, based around a die-cast JCB.
Building sites or maintenance yards are ideal scenic elements with which to fill a spare corner of a layout. They can be almost any shape or size, allowing them to fit into awkward areas. But rather than pose static items of plant machinery, how about making some of them move, just like the trains that pass alongside? I decided to create an animated bulldozer, taking an off-the-shelf 1:76 scale die-cast vehicle and a set of simple mechanical
components – combined with a little scratchbuilding – in order to create something eye-catching for a ‘OO’ layout. The main requirement was that the base of the builder’s yard had to be large enough to accommodate a geared motor mounted beneath the baseboard, as well as providing adequate space for the vehicle to move back and forth. An electric motor kit was obtained from Hobby’s (see panel, right), which provided most of the necessary gears and equipment. It’s worth noting that the same motor and crank arrangement described here can also be employed on a layout of any scale.
The star of the show is an Oxford Diecast JCB backhoe digger fitted with a bulldozer blade and a rear bucket, both of which can be posed in any position. In the real world, this type of vehicle might be seen loading or unloading aggregates or stone ballast. For model purposes, the digger is made to travel backwards and forwards in a straight line between a stationary lorry and storage. The chassis of the JCB is screwed to a sliding linkage arm, which is attached to a rotating motorised crank mounted under the base of the yard.
CONSTRUCTION The base of the maintenance yard, including the support for the geared motor and the crank arm arrangement, are constructed from 2mm (0.080in) thick styrene sheet. A slot, just wide enough to allow the JCB’S mounting screw to run freely within, was carefully drilled and cut as straight as possible. The geared motor was fitted to a simple but sturdy styrene support bracket, and two hinged rotating crank arms were also fabricated from the same 2mm thick styrene. The pivot was formed from a nut and bolt, with a washer placed between the two cranks to allow for free movement. A pair of nuts allow for a degree of slack between the cranks, without the parts working loose. The crank arm is fastened to the geared motor output shaft with a brass screw-type collar, fixed to the end of the arm with cyanoacrylate or epoxy glue. Measure and mark the position of the geared motor support assembly on the underside of the yard base to check the movement and alignment of the rotating crank and the sliding linkage arm. The motor support assembly can then be glued into position.
JCB ATTACHMENT The chassis on the JCB model is fastened to the body by two small screws. The front screw needs to be removed and replaced with a longer screw of the same thread size. This longer screw is used to attach the model through the slot in the yard base and into a pre-drilled hole in the end of the sliding link arm. The upper, redundant screw threads are filed away to leave a smooth finish where the screw is in contact with the sides of the slot. The model should pivot freely on the link arm. Three AA batteries, totalling 4.5V, with all of the supplied gear cogs installed in the gearbox, will propel the JCB at scale speed. Coarse sandpaper was glued to the yard base to replicate stone chippings, and also to grip the freely rotating wheels so as to prevent the JCB from skidding sideways. As an aside here, I found that one pair of wheels on my particular model did not rotate freely. This was remedied by gripping the steel axle with a pair of pliers and gently twisting the offending wheel clear of part of the body which was obstructing it. DRIVER WANTED I’d recommend adding the driver before modifying the vehicle for attachment to the sliding link arm. Prise off the roof of the cab with a knife to gain access to the clear glazed window moulding, then cut this away to access the driver’s seat. The chosen figure may have to be trimmed in order to fit into the cramped seat. I used Blu Tack to secure the figure and to reattach the cab roof.
SCENIC WORK Once the motor and JCB were working satisfactorily, the yard scene was completed by adding suitable buildings, fencing and gates. Stone ballast was placed in the storage pen and fastened with diluted PVA glue. A finer grade of ballast was then sprinkled over the ground where the JCB travels, while grass scatter material was used to replicate weeds, especially around the fence posts. Other items, such as oil drums, cable drums and figures, were glued in place to add the final touches.
Above: The principal dimensions of the maintenance yard and the crank mechanism. The position of the geared motor shaft/crank, and length of the JCB guide slot A, B, and C, are plotted from a diagonal line drawn between the two opposite corners of the yard base.