Over the Christmas period I have not done a great deal of modeling or drawing; the projects you’re waiting to see finished, such as the O Scale UP Water Tenders and the N Scale Atlas C-628 Dummy Chassis have edged a bit further, I blame the mince pies myself!  One thing I have been thinking about, whilst eating mince pies, are the projects that I will be working on in the New Year and the powered chassis which I will be using for them.  As it turns out this chassis might be a bit short so this means I will need to design a modification which can easily be inserted into the chassis to extend it. So to keep me busy I have drawn the power chassis ready to design the modification.

The new projects are going to use Con-Cor’s 4500 Gas Turbine chassis as pictured below.

This bulky chassis is also used for Con Cor’s U50 model.  It has a single motor which powers two of the four trucks.  The two inner trucks are dummy trucks but don’t let that fool you into thinking it is underpowered, all the mass of that metal chassis makes it a good puller.

To start with I modeled the main chassis as one piece, originally thinking it would work without modifications.  However once I began to see the difference it would create in the new shell I decided it had to be drawn properly.

So I then split it down into the two halves as shown below, taking note of all the lumps and bumps, so that when I design the extension piece it should be a good fit.

I have also drawn the drive shafts, these will also need to be modified or extended as they will be 5mm further away from the motor.  Extending these should just be a case of 3D printing a part that plugs into the end of the gear socket.

To make sure the chassis extension piece will fit correctly I have also drawn the motor, this is represented as a fairly basic block with the drive cogs protruding from it.  This is because all I am really interested in is its size and contact points with the chassis.

With all the necessary parts drawn I can assemble them in the 3D model as shown below.  Having all the parts in place makes it easer to see how to design the chassis extension.

The two halves of the chassis are separated by plastic strips, as shown below, which I have drawn in as these too may be affected by the extension. I choose not to draw the screws that hold it all together as they should not be affected and, after all, I still have the new shells to draw yet.

Here it is all assembled in the 3D model ready to start designing the new extension modification.

On the current chassis the two inner trucks have a center to center dimension of 51mm and for the first new model kit it will need to be 62mm.  Because the center of the chassis will be remaining in the same location it will need to expand by 5.5mm in both directions.  I will share with you how I have made the extension in a later post but for now here is a quick screen shot of one of the new shells in the very early drawing stages.

Now, where are those leftover mince pies…..