I'm new to the Lego train scene, although I've built up a decent collection of 9V sets over the past few years. This is my first real attempt at a MOC.

This gearbox connects directly to a standard 9V track switch (or set of points). Although the tabs for the yellow mounting lever are broken on this particular unit, the design still fits with those tabs in place. I've tested this on three different switches and it works fine. You DON'T need to open, cut or damage the points in any way for this to work. Instead, the Technic rack (3743) drops straight onto the points' sliding mechanism.

The old Technic 9V motor (43362 or 71427) sits on top, with the help of a couple of plates.

On the other side, a clutch protects the motor from stalling once the points have switched. I've tried this design with both the high- and low-torque clutches (light grey and dark grey centres respectively) and the points still switch and the unit stays in one piece.

Overall it's a very compact design. The footprint is 8 x 5 studs, but the protruding gears and Technic axle bring it to 8 x 8. However, it's really only two studs longer the existing point mechanism.

I wanted a design that used the older Technic motors because they're smaller than the newer stuff, very torquey, still relatively cheap and correct for the period (9V stuff).

As a small development, it's also possible to incorporate a gravity-driven signal mechanism into this design. Pay attention to the height of the white brick in these two pics:

In this design, the 1 x 1 x 5 brick (2453) has a 30 slope (54200) on the tip. The brick is held loosely over the end of the rack, so that it is held upright when the points are set straight, and then drops down when the tracks switch to the side. There's a lot of potential here for a "realistic" signal mechanism, but I don't have the spare bricks to explore this option yet.

Points in action:

Edited December 9, 201410 yr by Richfilth

I tried this out, but it didn't work for me with the torque-limiting gear at that position in the gear train. I had to move it earlier in the reduction stage.

It does seem to depend on the stiffness of the points (switches? switchtracks? I never know). I have ten here, and each one has a different stiffness due to the age and level of use. For the "worn" ones I made an even simpler gearbox where the 16-tooth motor wheel drives the clutch, which is connected to the rack shaft directly. For others, I've had to choose between the two clutch types (high and low torque). I haven't got a 16-tooth clutch gear available to test, but fitting that directly to the motor might help for some points.

I'm currently working on a slightly modified version, because this size has a tiny problem with very big wagons (lego sets 4560/4561, 4549, 4547 etc) - they just touch the corner of the 1x6 Technic brick as they turn onto the switched track.

Long cars will overhang and hit that gearbox. If you have anything longer than about 48 studs it'll be an issue.

If longer trains are running, it's perfectly possible to flip the gearbox design so that the reduction gears are the other side of the rack gear shaft. That will push the whole gearbox another three studs away from the tracks.

My design requirements focused more on being compact. This gearbox (complete with motor) can be fitted to two points face-to-face, and also fits into the 8-stud space between the two switched tracks. That way, it can be utilised for complex marshalling yards (which is my plan, once I find enough 71427/43362 motors)

Edited February 15, 201510 yr by Richfilth