Page 27 - July August 2017

for HO proper hence it was decided to procure several body shells to reduce unit costs and to insure against a construction disaster. The shipping and other costs of importing a single body shell into the UK are prohibitive.
The HO model would essentially facilitate a run through of the whole process of painting and detailing the body sidestepping the need for an HOn3 mechanism.
It was however decided not to install the interference fit glazing that came with the body shells so as not to risk damaging the delicate driver’s cab window frames. The black loco battery box did not take well to paint and in future models this has been left in its original state.
Initial trials used a DCC Concepts 6 pin Zen decoder.
For the final version power was routed via a Soundtraxx Econami diesel sound decoder fitted with Current Keeper and sugar cube speaker. The weighty brass plate chassis provided an excellent support for the speaker located
in the driver’s cab where the absence of glazing allows sound to escape.
The result of this effort was a very viable HO model and a step change in modelling confidence. If an HO model had been the ultimate aim it would of course have made more sense to purchase one ready to run from one of the Australian suppliers. This however was not the case.
The first HOn3 EMD G8
Following the success with the HO diesel the first HOn3 B-B mechanism was ordered from Hollywood Foundry with 10.5mm wheels. This has a single Mashima 1628
flat can motor powering a pair of belt drives via flywheels geared to suit a road-switcher. Interestingly it is under- stood that these motors use neodymium magnets. One flywheel has a smaller diameter than the other in respect of the narrowing of the body shell around the driver’s cab. The mechanism came mounted on a strong fibreglass sandwich board. Here there is a major difference with the HO model. Whilst the power drives for the HO model are entirely below the chassis, this is far from the case for the HOn3 mechanism where the motor, flywheels and upper part of the belt drives take up a considerable amount of space in the body shell itself. The HOn3 mechanism also benefits from the addition of self-adhesive weights into the body shell further reducing free space for the elec- tronics.
The installation of the mechanism required that the motor power connections were rotated to the vertical and insulated from the motor body, Soundtraxx units being installed high in the roof of the body shell while taking care not to place the decoder directly above the motor.
First HOn3 mechanism with Soundtraxx decoder and Current Keeper
First HOn3 mechanism inside unpainted Chassis
The challenge was how to mechanise this model in a simple and practical way. A B-B wheel configuration was chosen over three axles to minimise any possible issues with complex dual gauge turnouts and tight radii. Various motor options were ruled out because of size (Halling, Bull Ant), others because of poor reputation (Tenshodo and similar). Finally the choice fell between a pair of Steam Era Models’ Black Beetles and North West Short Line’s Stanton drives. UK stockists of Black Beetles (with 10.6mm wheels) resolved the question. Stanton drives are a little wider high up which might possibly have been an issue although that is not clearly the case.
The power bogies were mounted directly onto a stiff K+S 1” wide x 0.064” thick brass plate that in turn supported the body shell; the plate being reduced in thickness to 1.5mm around the bogie mounts in order to accommo- date the fixing bolts. This could not have been simpler although it did result in the body, and thus the gearbox sockets, being a little too high for HO and might have been an issue for a purist. The coupler problem was readily solved through the adoption of Kadee 145 overset whisker couplers in the interference fit gearboxes.
The instructions for preparing and detailing the body shells came in Portuguese and once translated proved to be quite sufficient. The most important point being that the resin shells need to be very carefully cleaned of any surface oils prior to painting.
Nairnshire Modelling Supplies provided the handrails and handrail knobs.
These were applied along with Humbrol Acrylic spray paints and Microscale decals. Single DCC Concepts mi- cro LEDs bonded to 2mm acrylic rod stubs were installed high up at each end of the loco body shell and side frames fixed in place onto the bogies using epoxy resin.
August 2017 - ROUNDHOUSE 27