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Zonker's LEGO(*) Train Turntable Page

http://BayLUG.org/zonker/ZTurntable.html
updated: 2002.1.21 dkzh

Navigation MenuThe "Great Project" these days is my LEGO Train Round House. This page is dedicated to documenting the turntable for the round house. If you would like to see more information on the round house itself, you can read my Round House Page.

I started the turntable as the first step in making my roundhouse project. The length of the bed itself (the length of 3 straight rail segments) was determined by the length of my own diesel design, and the longer car bodies in my collection. I wanted to have the longest bodies in my collection, plus a small tug, or 'pig' engine, on the turntable at the same time.

The base of the turntable, a large, blue gear from an early Technic Expert Builder Set, was a gift from a friend. Mounted atop a 4x4 swivel brick found in some early fire truck models, the gear provided a fine platform to build upon for the wide track base. However, turning this gear (which doesn't mesh with the Technic gears of today) was going to be a problem.

After posting pictures of the first part of the turntable, and discussing my gear problem with other local LEGO builders, Fred Yokel said he had the matching medium- and small-size gears in his collection. He gave me one of each size, and the small was perfect for the job!

Basically, the big gear is sitting on a 4x4 swivel brick. The next gear assembly is built up as follows: 2x2 swivel plate on the bottom, 2x2 round plate on the swivel, small white gear (to mesh with the big blue gear) on top of the round plate, and finally a 2x2 technic gear on top of the white gear, to make the connection with the gear drive assembly.

I've used a 2x4 brick, with side studs, to hold a technic worm-gear drive unit sideways. (You'll need to see the pictures.) Then I use two technic plates to suspend a small and large technic gear, as the interface between the worm-gear unit, and the small gear described in the previous paragraph. A long technic cross-axle is currently used to turn the worm gear, but the 8720 motor could be used as well. The walls of the turntable pit will support either method (manual or motor drive).

Another problem presented itself, when working with a turntable. Since the tracks cannot touch (which would keep the turntable from turning), I needed to develop a mechanism for locking the track into a fixed position. I did this with hinged elements, but added the feature that when a lock is NOT engaged to the turntable track, it holds up a 'caution' safety triangle, facing the engine in the roundhouse. You can view this locking mechanism in the open or closed position.

A secondary problem, as noted in the web page about Ben Fleskes' Roundhouse project, is that the polarity of the turntable tracks can become physically reversed when the turntable is 180-degrees from the normal position. (That is, take an engine in a bay, pull it onto the turntable, turn the turntable 180 degrees, and try to put the engine back in the bay facing in the new direction. The track will short as soon as the motor unit connects the turntable track to the track going into the bay.) To overcome this, I'll need to add some kind of polarity-reversal switch to the electrical leads that will power the track on the turntable.

Matt Bates has been investigating the use of miniature DCC train controller circuits, adapted from normal model railroad equipment. (You can get more info on his Matt's Train Depot web page.) This probably won't help in this case, however, because the LEGO train motor would connect the two sets of rails when the engine tries to leave the turntable in the polarity-reversed position. :-(

The turntable is currently made of three straight track segments. Based on the fact that I cannot overlap rails for my own roundhouse (without painful 'plastic surgery' to my track), I will need to have my rails meet side-by-side. By putting the tracks as close to each other as possible this gives me a track/radial every 20 degrees (minimum).

Since LEGO curved track is only available in 1/16th circle sections, I used 22.5 degree spacing, which is 1/16 of 360 degrees. The potential track layout for the five bays will look something like the image at left.

The hole for the turntable (shown in grey in this image) is about 17 inches in diameter.

The bays are numbered from left to right. The vertical section in this image is bay #1, working around to the horizontal section, bay #5.

The red outline shows the proposed edges of the roundhouse. The wider area at the upper-left of the image is the workshop, next to the tracks.

I figured I would need a large piece of wood for the surface, since these radials wouldn't match up with standard base plates. This would mean cutting a hole in the wood for the turntable (and creating a supporting structure for the grey base plate that I'll be using for the turntable). Currently, the round roundhouse will cover a 3'x4' area, with some outside 'yard tracks'

I also have a few ides for the signals in the freight yard itself, but I'll need a lot more straight track and some switches. I'll also need a bunch of the wire clamps that pass electricity to the rails. (Sigh!) I also have designed a small circuit for an LED Train Signal you can try to build.

I've added the newer 9-volt electric motor to the turntable, with OK results. The newer motor kits come with a 'clutch' gear, which I'd like to use to allow for a manual over-ride, in case the batteries give out. I've also decided I need to add some step-down gearing, more to reduce the speed than to increase the torque of the drive. This is so I can try to line up the track as I turn it, since there isn't an automatic method to engage the bed of the turntable when it is close to the right location. (This experimentation has been delayed due to long work days, and earlier sunsets. But there are some rainy days in the near future, so I may get back to this project soon. :-)


Disclaimer:
These pages are NOT sponsored or endorsed by the LEGO companies.
They are the creation of an enthusiast of LEGO bricks.
The official LEGO home page is www.lego.com.
(The LEGO companies have their own pages. This page is mine. :-)


Copyright 1996-99, David K. Z. Harris, N6UOW
Questions? Comments? Additions? Email
frenezulo at baylug.org

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