As you may have noticed from last week’s post I am getting back into the drawing and I’m trying to wrap up some of the outstanding projects. This week I’ve been working on the dummy chassis and trucks for my N Scale Alco C-855.
This also has the advantage of providing all the parts to make a dummy chassis and trucks for Con-Cor’s U50 and 4500 Gas Turbine locomotive shells. I’m sure there are a few spares knocking about now several have been converted into C-855s.
As with all the dummy chassis kits it’s the trucks that take the time. This is because this is where all the detail is. The C-855s, U50s and Turbines all had the same truck designs, in fact the same trucks were recycled through the engines. The original 4500 Gas Turbines were built under the Alco-GE (General Electric) partnership. Alco went on to build the C-855 and GE the U50. The wheel arrangement is specified as B+B+B+B. This means there are four two-axle trucks with all the axles powered. The first and second trucks are linked with span bolsters, as are the third and fourth. In the image below of a Con-Cor 4500 Gas Turbine, with one of my battery box kits, you can see the truck arrangement.
The first and fourth truck on the model are the only powered trucks and are connected via a gear tower up into the chassis. The second and third trucks are connected to the first and fourth via a span bolster or draw bar and clip into the battery box.
To draw the truck I normally start with a rough image scaled to the correct size, then using actual dimensions I draw the side frames in 3D.
Then I assemble the frames to form the truck, ensuring they are correctly spaced for the wheel sets. Depending on how the truck will be connected to the chassis will depend on the truck construction. These have a central bolster pin.
The truck isn’t actually finished yet. I still need to add the span bolster section to join the two trucks together and, as you can see, this will be one of the first or fourth trucks because of the bolster pin.
One of the challenges I have with this design is weight. As the first and fourth truck will be carrying the weight of the loco they will stay on the track but the second and third won’t be carrying weight. 3D printed parts are very light, even with metal wheels, so this will make the trucks bounce about. To solve this I will be looking at a 3D printed stainless steel insert, as with the original Con-Cor truck. This will ensure the truck stays on the track and will help them track around corners.
The chassis is an easier issue. As you can see below it is a fairly simple design. Because of the size I am planning on printing this in the WS&F material simply to reduce the cost as I did with the EMD DD40AX dummy chassis.
As I’ve already drawn the Con-Cor chassis in order to work out the extension parts and correct fittings for the shell, all I had to do was copy the shape. In the image below you can see my model of the C-855 powered chassis next to the dummy. I have left the same mounting points on the fuel tank allowing the shell to clip directly on and there will be ample room inside to add some weight. Again this is important as the chassis and shell on their own will be very light.
Interestingly these three locomotives differ from regular locomotives in that the couplings and pilots are part of the truck and not the body. Normally a diesel locomotive’s strength is its chassis and the couplings are attached to the end of it. The load of the train is transferred through the chassis and the trucks provide the thrust up through the bolster pins. Most early models of locomotives positioned the couplers on the trucks to make them navigate the un-prototypically tight curves on model railroads. However the locomotives with span bolsters do have the couplings on the trucks and the load of the train is transfered through the trucks. The chassis simply rides in the trucks and provides weight for traction. This means I also have to draw the couplings and pilots on the first and fourth truck.
To make the U50 and Turbine dummy chassis it will simply be a matter of shortening the C-855 chassis and changing the centre section to accept a fuel tank or battery box. Once I have solved the span bolster section and drawn the couplings and pilots I will share the next step with you.