Time has flown by and it is already three years since Percy emerged from the paint shop as GTR 2543. For those unfamiliar with the tale, the eight-month saga whereby Thomas the Tank Engine’s cheeky friend, Percy, sacrificed himself for science and good-running can be found here.
The most significant discovery of the period is that, when running flat out, the little electric motors inside our models pack a punch heavy enough to dislocate drivers. The accepted wisdom has always been that you should cram the biggest motor into a locomotive that will fit. It is a rule that has stood since the days of the hand-wound open-frame motors. The rule sounds good, and the motors on #10 and #622, just barely slip into the boilers. In the case of #10, in particular, this made a model that is mostly air, and has the pulling power of a 7-legged daddy long legs.
A more nuanced rule would balance the weight of the model with the size of the motor. The motor needs to be large enough to slip the models wheels so it doesn’t burn out. Yet it should be small enough to allow the maximum weight on those wheels. Just how small can the motor be?
Enter Percy again – the little engine that is designed to be a test-bed for these questions. I’ve found some truly tiny gear-head motors, and Percy’s tank has lots of room for weight. Can one of these tiny motors pull a train? There is only one way to find out.
I picked up some 0.3 mod gears from Northwest Short Line a few years ago, and Doug Hicks kindly gave me a little bag of worms and worm gears. So this week, I designed a couple of options for the drive train. The motor shaft is very short, so both my designs transfer rotation via spur gears to a second shaft that carries the worm. The first design is long, and the second is more compact. I’m favouring the second.
Pembroke:87 
rene – WHile Option 2 looks easieer, option 1 might be appliciable to more of your locos.
It might be. The thing I like about option 2 is that it might fit entirely into the firebox, leaving the back head intact. This is a greater concern for #10, which has a nice blackhead.