Scratch Building a Gas Mechanical "Critter"

Over the last several years I have been slowly working my way through the Achievement Program of the National Model Railroad Association.  The AP provides incentives to learn and master the various crafts and skills necessary in the hobby of model railroading.  For each category (scenery, structures, track work, wiring, etc.) there are requirements demonstrating your skills.  Successful completion of the requirements earns a certificate of achievement.  Earning seven or more certificates is recognized by the title Master Model Railroader.    I currently hold five certificates: author, electrical, scenery, structures and prototype modeling.  This year I have started on the Motive Power requirements.

This AP category has only three requirements: Build a superdedailed locomotive from scratch and build two other engines that can be from kits, but must also be superdetailed.  Motive power is not as intimidating as you might imagine.  It isn't necessary to scratch build a brass steam engine with all the valve gear and rods.  You can choose to build a diesel locomotive, a street car, or just about any other kind of motive power you can imagine.  I have chosen to scratch build a gas mechanical "critter" based on a photo of an S scale engine I found several years ago on the internet.

I was immediately smitten by this little engine, apparently some kind of gas mechanical switcher.   Here is another view from the rear.

Since I model in HO scale, I decided to design my critter as an HO gauge locomotive.  But I wanted to keep the quaint character of the photo, with its wood decking and cab, the odd windows, the lights and air tanks on the roof, etc.

I am building my critter around a Stanton Drive from NWSL.  The Stanton is a self contained power truck unit that can run on either DC or DCC.  The drive is small enough to fit beneath the deck of the critter, with a 10 foot wheelbase that was just about right for the model.

I have an old Lifelike Plymouth industrial switcher that looked to be about the right size for a Stanton Drive, so I used that to estimate sizes for the side frames and beams, as well as overall length and width.  The superstructure of my critter will be made of Evergreen styrene, which is easy to work with.  The problem, of course, is that such a small engine made entirely of styrene would be very light and have power pickup issues, so I decided that the styrene frame would have to fit over a brass underframe to give weight and strength to the critter.

 I cut a piece of thin sheet brass to the estimated size of the deck, plus the height of the side frames and end beams.  Then I cut out the corners so that the entire sheet could be folded, using a small bending brake from Micromark.  The result was a rectangular box open on the bottom.

The next step was to solder the corners of the brass underframe. I clamped the sides using popsicle sticks to press the corners together.

I applied a liberal coat of TIX flux, and soldered the corners.  The final result was a brass box around which I would form the styrene side frames and end beams.

In order for the Stanton Drive to fit properly inside the underframe, I had to cut out a rectanglar opening in the top of the box.  The raised center portion of the drive mechanism fits in the opening, while the lower parts are secured to the inside of the box with double sided carpet tape.

Here is the motor mounted inside the underframe.  The side frames and end beams will be cut to fit around the box, then glued together using the underframe to keep the assembly square.  At this point I was able to do a test run of the motor and underframe assembly using standard DC power.  The drive ran well enough, but it was evident that even more weight would have to be added for good pick-up.

Notice that there are four wires coming from the Stanton Drive, colored red, black, orange and gray. The red and black leads are for track power, the orange and gray are the motor leads.  If one connects black to gray and red to orange (as shown) the motor will run on DC.  I plan to connect the red and black power leads to a Soundtraxx model MC2H1040P mobile decoder.  The decoder orange and gray leads will then be connected to the drive 's orange and gray wires, for DCC conrol.  The MC2H1040P decoder will run on either DC or DCC, which is an added convenience.

In the next installment I will discuss how I built the frame, decking and superstructure for my little "critter".