This is a simple locomotive designed to operate operate around tight curves such as those found on wooden railways. Hence it will also operate on Plarail. The wheels have flanges and treads so it will also run on 0-gauge track, e.g. the fully printable OS railway, vintage BigBig Train track, vintage Hornby and Lionel tinplate track, also modern Lionel/Disney supermarket train sets.

As with some industrial locomotives the couplers swing from a pin in one of several slots.

All parts are designed to be printed on an old Tiertime with a 100mm bed. You may wish to rotate some parts for printing so as to minimize supports.

The motors are cheap yellow geared motors with an output shaft on each side. The nominal voltage is 6V but they run well enough on 3V. You will not find these motors on a Mars rover.

These locos are reasonably powerful. Here a couple of them are pushing a 16mm livesteam Davenport. It was cold but well oiled. https://www.youtube.com/watch?v=Ds6BBcSa9is

Here is one pushing a long train of small toy cars (meant for wooden railway) on a vintage 3-rail 0-gauge layout: https://youtu.be/rDoBWMdphGs

There is only one switch hole in each version of the cabin roof. In Cabin 2 you can use a square push-on-push-off button in series with the battery for toddler-level simplicity (like the Thomas family for wooden railways). In Cabin 3 you can use a 3-position centre-off double pole toggle switch to allow for reversing.

Ideally you should have both switches and eventually I'll add a version with holes for both. Meanwhile my reversing switch pokes out from one of the side windows. Likewise the optional charging point pokes out of a front (or back) window.

Electrics

• There is room for a 2xAA battery holder in the well between the motors so the simplest arrangement is to wire this in series with the on-off switch and connect to both motors in parallel (not series).
• The next level is to use a reversing switch in place of, or in addition to, the on-off switch.
• The next level is to use a small 3.7V lithium cell and a charge regulator board (say one intended for Arduino toys). Wrap the board in tape and just have the USB socket sticking out a window. The loco will run a little faster due to the higher voltage.
• The next level is to interpose a 5V USB power board between the battery and the motors. The loco will now run fast enough to keep up with other models on an outdoor track but it might appear to be a bit too fast for a wooden railway!
• After that you could add a variable speed controller or even radio control, see other OS railway models to learn how it might be done.
• At any stage you could add LEDs in the headlight holes provided.