· Cable Car

May 2007
            

The first true working LEGO Cable Car.

After our trip to San Francisco in December, I immediately wanted to recreate a working Cable Car that would actually be hauled by a cable hidden beneath the tracks. (hit the link for more info on Cable Cars)
Well, after months of building, not building and then building a little more, here's the result. Check it out!

A comparison with the real thing. It is modelled after the California Line Cable Car, which has driver controls on either end of the car.

The challenge was to make a vehicle capable of moving on LEGO railroad tracks with LEGO wheels. But since the grip (that's what the "claw" beneath the vehicle is called) has to go below ground between the tracks, a new solution had to be found.
The trick consists of using two sets of tracks, set apart so that the outer edges of the inner rails of each track are at the correct distance for LEGO train wheels to run on them. Look at the picture:

Here you can see the LEGO grip. At the height of the tracks, it is exactly one stud wide. This can be seen when it passes over the gray 1x8 plates with door rails, which remove half a stud from each side leaving a one stud wide gap in the middle.

The grip then holds on to a moving cable below the tracks to move forward, and releases it and brakes to stop. In this prototype version the cable and its powerhouse are not finished, all tests were conducted using a cable pulled by hand. But the grip worked just fine.

This is a simplified LDRAW image of the grip mechanism.
The motor powers the system over a worm screw (blue). The power is transmitted to a 8t gear (green). This slides the 1x8 gear rack (red) which transmits the movement to a second 8t gear below ground (yellow). The grip mechanism uses two 16t gears which engage the gripping claws (orange), making the Cable Car hold on to the cable (cyan).
The tracks are at a height exactly between the two 8t gears, this way only the gear rack must pass between them. The whole grip mechanism is held in place by two liftarms one behind the other (see below), so it is just one stud wide at track level.

Another feature is the emergency brake, which presses two rubber tires against the tracks to stop the car.

The second picture shows the brake (the green 1x2 brick next to the light sensor) as well as the grip.
By the way, the light sensor can be used to read color markings next to the tracks. Possible uses include stations and end of track markings.

The entire body can be detached by simply removing four pins (one on each corner) and then lifting it up, so only the chassis with the RCX and the mechanisms remains. This allows for easier building and troubleshooting.

Some shots of the gearing for the emergency brake. The tires are attached to the liftarms on the right of the first picture, over a rod that pushes them down when the gears rotate.
The motor on the right is actually the grip motor (you can see the worm gear deep inside if you look closely), the brake motor is next to the white clutch gear.

Notice on the second picture, you can see the grip motor on the far right, the liftarms that surround the motor shaft are actually the ones powering the brake, one on each side of the motor. Talk about compact mechanisms!

The RCX can be accessed through a magnetically secured hatch on top of the Cable Car.

A few more shots. Please comment on the design and the mechanisms involved, I need feedback if I want to build an improved version!

Last but certainly not least, a little YouTube video demonstrating some of the main features. Enjoy!

[High-Res pictures available]

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