An­i­mate a JCB

Graham Good­child cre­ates a work­ing cameo scene, based around a die-cast JCB.

Model Rail (UK) - - Contents -

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.

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