So I set out to build a monorail out of LEGO pieces that are currently available. My goal is that the rail itself should be simple to build; ideally a one-stud-wide wall of some minimum unobstructed height. I decided not to put tile on top of the wall, partly to keep the track design more economical, and partly because the studs provide better traction than a smooth, tiled surface. I also considered building a wider shelf beneath the rail to help keep the train stable, but I have found this to be unnecessary.

To date, I have built several prototypes with various levels of success. The early ones used wheels mounted horizontally to ride along the sides of the wall, but I found that this design was prone to riding up the rail, and also tended to bind in corners. I have since found that Technic Pin Connectors are the perfect rollers to contact the wall. They roll easily and have a smooth surface that would drag without much friction even if they didn't roll. When mounted with a one-stud gap between them, a pair of these easily fit over the rail and support a monorail without any threat of derailment.

Gearing the motor was another challenge. I wanted to keep everything compact so that the monorail trains wouldn't be gigantic. However, I found it necessary to reduce the motor speed significantly in order to achieve scale speeds that didn't literally tear up the track. In these situations I find that a worm gear mated with a relatively large circular gear provides good reduction in a small space. As shown, it still runs a little faster than I would like.

The engine, shown in the pictures without a battery box, is capable of running along the top of a straight wall that is at least two bricks tall. It can also climb modest inclines (up to about 30 degrees) without any trouble. This in itself was an exciting achievement, and was an important milestone for the project. I have made curved rails using ZNAP parts which do not derail the engine, but the radius is so short that my drive wheels come out of line with the rail and the engine stalls in the turn. I can correct for this if I can put a pair of pin connectors right at the drive wheels instead of in front and behind, as in the current design.

I have yet to make another pass at this design. I recently acquired a real LEGO monorail set (Airport Shuttle) and some extra track, and I have been playing with that. I don't know if having that set will dampen my interest in this project, but I hope it does not.

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