Image Darjeeling Himalayan Railway Diesel Locomotive in 4mm scale


1. The ‘Bullant’ power unit, and the frames/spacer assembly A crosspiece has been added near the centre of the ‘Bullant’ which will rest on the two brackets near the centre of the frames. The cut-out in the frames is to engage with the plastic support on the motor unit which would normally locate a bogie sideframe; it will be hidden by the fuel tank.	The spacers have a hole front and rear through which the body fastening bolts will pass. I decided that the power unit would be installed with the flywheel to the front, to minimise protrusion into the cab, so I used the two mounting holes on the ‘Bullant’ (for which bolts are provided) for fastening to the front spacer. However, I did not wish to have the chassis and body supported as a cantilever from only one end of the power unit, so I added a brass cross arm to the top of power unit, under the motor, with tapped holes at each end. This rests on two brackets soldered to the inside of the frames and is secured by bolts from underneath. With this arrangement, the power unit is firmly connected by four bolts from underneath.	Above The breakdown crane (see CM November 2002) lifts the NDM6 body clear of the chassis to reveal the motor and flywheel.
Power unit While I was intending to build the chassis from scratch, I was not confident of my ability to build a sufficiently smooth and reliable power unit, so I looked to commercial offerings. Aside from the incorrect sideframe detail, the Kato tram chassis has too long a wheelbase, and the wheels are a trifle small for accuracy, so that was not an option. I decided on a ‘Bullant’ four-wheel power unit, produced by Hollywood Foundry (which, despite the name, is located in Melbourne, not Los Angeles). ‘Bullant’ drive units are made to a well engineered standard design and are available in a range of dimensions, gauges, and drive types, to the purchaser’s specification. I ordered a unit for 9mm gauge with a 22mm wheelbase, 8mm disc wheels, and a 27:1 belt drive. Gear drives are also an option, but I chose a belt drive for smooth low speed running. The ‘Bullant’ unit is smooth running and sufficiently powerful to handle a five-coach train, though three or four coaches is likely to be the most it is asked to handle. The unit is intended primarily to be used in a bogie loco and includes provision for mounting into a bogie frame, but it is equally suitable for use in the chassis of a four-wheel loco. So, the choice of power unit was easily and effectively resolved. The frames Prior to making the frames into which the power unit would be mounted, I completed the body kit (a real delight) along the lines described in the previous CM article. However, I made up the body/cab and footplate as two separate assemblies to assist in ensuring that the power unit would fit correctly. It also helped when the model was to be painted. The frames form the core of the model; they are supported on the motor unit, and in turn they support the footplate and body. Two pieces of 0.4mm brass, 64.5mm x 9mm were assembled with spacers at the top giving 13.5mm clearance between the frames, sufficient for the ‘Bullant’ unit.
		2. A trial assembly of the frames, motor unit, footplate and cab, to ensure that all fits comfortably. The motor protrudes into the cab, but is below window level.
		3. The relationship of the frames to the footplate (with the fuel tanks fitted). The units will be connected together by bolts passing upwards through the holes at front and rear, into the body.
December 2010	801
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