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Zonker's LEGO Round House

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[Early design options pictures!]

[I need a table for this!]
The table design becomes final.]
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[ Making the turntable turn!

(updated: 03.4.21)

This page is getting longer! I'm leaving the old stuff, turning it into a Web-Log of sorts. I wanted to capture some of the reason's for doing things one way, and then later pointing out what made me change things to a different way. But, it just got to the point where I need to re-organize it a bit, to make it easier for folks to find the stuff they want. Please bear with me while I move things about a but.

The start, Summer 1997. During our summer trips to Europe, I have visited a number of train yards in Spain, France, Poland, Germany, and the Czech Republic. When it was allowed, I took photos and/or video of the trains, train yards, main station houses, and work trains. In Poland (1996), I took some good video of a working round house in action. Because of this round house visit (and the good luck of finding the discontinued Load n' Haul freight railroad in Poland), that I decided I would try to make some models based on trains I have seen in Europe and at home in the U.S., including a working round house. To that end, I bought all of the rail-wheel sets, magnetic coupler sets, and the boggie plates for the rail wheel sets from one small shop in Prague which carried a large collection of Service parts. I also bought some interesting Technic gearing sets with the intention of using them to build switching and signal models.

My first train creation (while waiting for the freight train model to arrive from Poland by postal mail) was a large, yellow diesel engine, ala the Union Pacific Railroad. After building the big diesel, I also built a smaller freight-yard engine. (You can see both engines on my engines page.) About the same time, I finally decided that my next Big Project would be a working round house for my LEGO trains. This would require destroying the large Fire Station project that had been my labor for over a year, in order to use the roll-up doors for the five diesel engine bays.

I've discovered that the roll-up doors have their limitations...for example, you can only have 12 window segments in the overhead rail. Since most train cars are longer than this overhead rail, I can't let the door come down from the back. If I used 13 or more segments, the door would hang down from the overhead rail, and impair the clearance in front or in back of the overhead rail. Also, given the constraints of the overhead rails, there is a limitation of 10 of the 1x2 slotted bricks that form the vertical rise. (If you have 11 vertical bricks, the door will have a gap at the top.) On my mock-up of a garage bay door, I use a plain 1x2 brick at the foot of each front pillar, so that the door segment does not rest on the rail. This is equivalent to the height of the track tie and rail, leaving 10 bricks for the vertical rise for the doors. The links below show the first mock-up of the bay doors and supports.

I have already created the basic turntable, using a large, blue technic gear, so that the turntable can be run by a crank or a motor. There is a separate turntable page that documents how all of this works.

I built a version of the round house with 3 studs between the hinges and the door frame, to see how close I would need to be to the turntable. I tried 4-studs, and 5-studs spacing as well, to determine the best spacing for me. (The more stud spaces between the hinges and door frame, the farther back from the turntable the front walls will need to be.)

Here is what the first version of the roundhouse and turntable were going to look like. The turntable is about 15 inches (three straight track segments) across, and the five bays span 90 degrees of arc. This leaves a 22.5 degree angle (1/16th of a circle) difference between each of the bays. This works well, since LEGO curved train track segments are also 1/16th of a circle. The red outline shows the basic layout of the roundhouse, as I originally planned it. The track layout artwork is courtesy of Matthew Bate's Track Designer program, available from Matt's Train Depot. Sadly, the program is only written for Windows. :-(

Unfortunately, this setup is too big to fit on a Modular Train Table, even a large module. I hope Matt will add the table outlines to Track Designer. :-)

After the first couple of attempts, I began working on the round roundhouse in earnest. The results are shown in the next few photos. I have installed red and green transparent 1x1 round plates (lenses) on the frame of each door. I have the ability to put small LED indicators behind these, shining through the 1x1 brick that supports them. My plan is to use a single switch to connect one rail to the train controller, and have the same switch connect the LEDs to a blinker circuit. (The other rail would be connected to the train controller directly.) This way, I will have a visual indication of which track(s) are 'live' at any time. Someday, I'll even be able to switch from the green LED to the red LED when the train reaches the end of the track!

I have also managed to acquire a matching gear to the old, big, blue gear I picked for the turntable base from Fred Yokel in San Jose, CA. Pictures of the gears are on the Turntable page. 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).

The Rectangular Roundhouse

When I saw what looked like a lot of wasted space between radials, I thought about using some curved track, to try to make the tracks within the roundhouse parallel to each other. This experiment resulted in the following notes.

Overhead view of Straight HouseBased on a 5-bay design (because I only have enough parts for five doors), I decided that bay 3 would be a straight radial from the turntable. The tracks to bays 2 and 4 would have one curved segment that meets the turntable, and then they become straight segments. Bays 1 and 5 would have two curved segments, and then they become straight tracks.

With this design, the separation between the ties between bays 2 and 3, and between 3 and 4 would be 5-studs. The separation between the ties for bays 1 and 2, and bays 4 and 5 would be 8-studs. Because of the curved track, the front edge of the bays would need to be at least 21 studs from the turntable edge of bay 3. However, if I want to get long-frame cars and engines into bays 2 and 4, the setback moves to 23-24 studs, and if the long cars go into bays 1 and 5, the setback moves to 28 studs from the turntable!

Now, figuring that I need at least 2.5 straight track segments within each bay, to allow for the longer cars, that means that the back of the bays would be at least 28 inches from the edge of the turntable.

The track spacing (with ties being 8-studs wide) looks like this;

 [TIE]<8 studs>[TIE]<5 studs>[TIE]<5 studs>[TIE]<8 studs>[TIE]

That makes the track area 66-studs (20 inches) wide. Add at least 1-2 more inches from wall to wall. Suddenly, this thing started to look B-I-G!

Advantages to the rectangular roundhouse (so far)
+ design seems easier and neater (more compact)
+ it will be easier to make the roof (maybe use large building plates?)
+ a service crane could slide over many tracks, instead of just one

Disadvantages to the rectangular roundhouse
- curved tracks impose added distance between turntable and bays.
- the curved sections also change the length of bays (2 and 4 are the
deepest, bay 3 is shallower, and bays 1 and 5 are shorter still.
(With a roundhouse, straight radials mean bays will be the same depth)
- it's a bit strange (aren't roundhouses supposed to be round?)

I decided that I liked the challenge of building a curved face to a building, and the use of hinges and roll-up doors made this pretty easy. I wanted to build a round house, and not a straight house.

About June of 1998, the round house construction came to a halt. As work had been progressing, I would fold the round house up (see photo to the left) using the hinged walls, and carry it outside to take pictures of the progress. Unfortunately it was finally getting so big that it was starting to sag under it's own weight as I moved it.

I decided that I needed to build a table for it, and install the turntable into the table, before I could continue to build more of the round house. Up to this point the round house and turntable had been separate projects. Now, they needed to be merged.

I had originally used a 4' x 4' piece of 5/8" particle board for laying out the round house. I figured that was a common size, and I could attach it to a 4' x 8' layout later. I hadn't thought about legs, since I didn't have space for a permanent table. I picked a turntable location at random, and figured out where the radials would go from there, tacked some track down, and then put the building face around the tracks, to see how things fit, and take pictures in bright daylight.

Later, I read about the modular tables used by the PNLTC. They used a non-standard size (i.e. 'not even U.S. feet or inches'), which was chosen to fit LEGO part widths (i.e. 'studs'), rather than inches and feet. The table heights were also set, picked so that it was a good height for kids to look at them, and so that various members could build these tables independently, and then bolt them together at train fests! The design included a square and a rectangle (two squares side-by-side), allowing lots of possible combinations.

I decided to use the modular tables, designed by PNLTC member Ben Fleskes. I chose to use the modular tables so that I could mate my roundhouse to other layouts later, when I find a few more trainiacs in the S.F. Bay Area. You can find the building instructions for the modular train tables here on

In November of 1998, I had built a large and small table module, only to find that the turntable and the original round house would not fit on the large module at the same time. (you can see how the roundhouse seems to stick out over the far side of the table in the photo to the left.) And, due to the overlap needed between the round house and turntable, the two models couldn't be built on separate tables without a major redesign of the buildings or track layouts. I also didn't want to have to bolt two tables together all of the time, since the overlap didn't take much space. I realized that I couldn't count on having enough space on a nearby module, and I also didn't want to have a portion of the building unsupported. Occasionally, I'd try to find a way to make them fit on the large module, without success. Again, building was halted, until I could solve this puzzle. In the meantime, I also designed a small electronic circuit for LED-based train signals., and some rolling stock, helped get BayLUG started, and launched the BayLUG website.

In May, 1999, I finally had the breakthrough I needed. After the first 'Official' BayLUG get-together, I invited a few members to visit my home, and see my LEGO building area in my badly cluttered garage. During the visit, one member accidentally bashed part of the round house wall with his elbow as he was turning around. Later, when he turned to show the others the damage he had caused, he accidentally bashed it again, this time with his hand. He left that day feeling a bit like Godzilla! I didn't really survey the damage for a week, after all, bricks go back together, and I had photos to work from! While the damage wasn't catastrophic, it was significant enough that I could choose to rebuild it the way it was, or I could save the bay doors, and redesign the rest of it.

While considering the redesign option, I decided that I really wanted the turntable and the round house to both live on the same large module. Having decided that, I needed to consider placement of the turntable, because I didn't want this below-the-surface construction to weaken the table frame, or to interfere with the structure for bolting it to other modules, since the turntable would also be connecting to the train tracks from those neighboring modules/tables.

I chose where the turntable would live, without interfering with the table frame structure, and tried setting out a few possible track layouts on the tables surface. Early in June 1999, I finally made a bunch of sawdust, cutting the hole for the turntable to pass through, and made a mounting system, so I could easily remove the turntable. (The LEGO parts in the photo were used to align the marker track to the 22.5 degree angles to lead into the Round house bays, and to mark the radius of the hole for the turntable!) Later that week, I began working on the track layouts, and on putting the face of the round house back on the table. I took pictures along the way, but the negatives somehow turned out all white for the LEGO pictures, even though other shots on that roll were fine.

Here's a look at the basic track plan for the new roundhouse The Office/Shop area is about the same size as before, but the opposite wall has been moved in quite a bit. Bay 4 and Bay 5 are very shallow, so I can only fit a small transfer engine or other short wagon in these bays. (That back wall is actually on the edge of the module. No overhang, but tricky none the less.)

This illustration was made with Matt Bate's fine Track Designer 2.0 program for track layout, run through MS Paint to add the colors and show the building footprint and saved as a bitmap, then strained through Adobe ImageReady to make the colors web-friendly and add the text.

I decided to use a couple of curved track segments within the round house, so I could have some parallel tracks under a service crane. I've tucked two 15" x 15" large grey base plates under the three parallel tracks, to support a work area, and give me a base to create a service crane within the roundhouse. To make the crane simple, I actually turned the second and third bays a bit (1-curve, and 2-curves, respectively), to make them parallel to the first bay. But, this creates an odd height problem, since a base plate is about 1/2 as thick as a plate. I can't use base plates under all of the round house without cutting up a few base plates, since there are odd-angled track, curved tracks, and the odd angles of the face of the round house being made of hinges.

Photos of the new design, fall of 1999.

I've made a lot of progress over the past few weeks, and I've made some interesting adjustments along the way. Since a couple of the bays are relatively short, I've modified the windows along the long back wall, adding a ventilation system, work bench, and sink and shower (for chemical accidents). I've also had to redesign the shop area, and changed the roof access a bit. I'm working on those safety features that a U.S. OSHA inspector might want to see, and I've used some older rail ties along the base of the long walls, so I can help anchor the walls to the tables, to keep things from sliding while shipping. I also need to track down another freight loading station, to get the elements for the overhead service crane.

I still need to work on the vertical alignment of the turntable. The cradle for the turntable is between 2-3 plates too shallow, so there is quite a drop onto the turntable, even when the radials are aligned. I'm going to try to use a sheet of rubberized canvas below the grey baseplate under the turntable. (Folks with small boats may know this stuff, since they use it to keep stuff on the shelves while under way.) The height should be close, and it'll help keep the turntable in place without needing to use glue or screws. I may still need to redesign the turntable supports to help get the track heights to match.

During the beginning of July, I mounted the track power contacts, and drilled holes near the contacts, so I could drop the wires under the table. Of course, that meant cutting the power cables. I still need to decide where I'll control the track power from, so that I can run cables there. I'd better get to work on my track power switching board, and my timer board. I'll also need some LED signals pretty soon after the the round house is done. I also need to drill holes for the LEDs that will be mounted in the lenses along the front wall, and connect the wires for the LEDs for each bay into the same connector as the track power for that bay. I also need to redesign the turntable a bit, to allow me to pass power cables for the trurntable track safely out of the turntable bed area. Then I need to route the power to the motor that will turn the turntable...

Photos of the new shop design, and new walls.

Spring 2003. The roundhouse made its public debut at the Daly City GATS show in August of 2002. The turntable, like always, suffered from the trip to the event (just like it did when I took it to the BayLTC meetings...). We put a few pieces of "Yellow Equipment" around the pit, and explained to the visitors that the turntable was still under construction.

Because it was still fairly fragile, I was reluctant to ask other club members to handle moving it to the November GATS without me there to help rebuild it. Over the winter holidays, I worked on rebuilding the back of the roundhouse, to add strength, and I also added some partial roofing (high-slope bricks) to help add some rigidity to the back of the roundhouse, and give it a bit more of a finished look. But, the turntable still needed help.

From time to time, I had tried to solve the problems. The two main issues were;

  • there was a 1/2-plate gap under one end of the turntable support wheels, no matter which types of wheels I tried, so the turntable would rock, and it was hard to keep rolling stock on it when the turntable rotated.
  • I had not found a reliable way to turn the turntable. That is, I didn't have a soulution that would stand up to a day-long public display without needing to be rebuilt a few times during the day.

Finally, I decided to try a few options that were NOT wheels. I tried the 2x2 'bubble skids' that you see under boat models, but I finally settled on the small skis and some 1x2 finger hinges. These slide well, but can overcome any tiles that rise slightly during transport, or during the shows. AND, these will sit flat on the tiles, without that gap that the wheels had! The only downside to this solution was that I had lowered the surface of the turntable track by a couple of bricks! (This would be bad, since I used to have a large 9-V motor in the bay, trying to drive the gears...)

The well for the bay is 6 bricks and 2 plates deep above the large grey baseplate. I built a couple small baseplates, with some 2x2 pillars, and a couple support plates, and put a piece of straight track on top. Putting these on the table with the new turntable, I saw that the vertical difference was a bit more than 2 bricks, but not by much, so I built some 2-brick-tall supports, and put them on the table, and rested the turntable base on these supports. The height was PERFECT! Now, all I had to do was find a way to turn it...

Turning it just got a bit trickier, since the motor and mechanisms would have to fit under the rotating track structure of the turntable, only 4 bricks of vertical space! Since I didn't want to use a micromotor, I'd have to put the motore outside the turntable pit, and transfer the motion into the gearing somehow.

    Let me digress a bit here. I spent much of the fall, reading the most-excellent Building Robots with LEGO Mindstorms book (Syngress Press, ISBN 1-928994-67-9) by Mario and Giulio Ferrari and Ralph Hempel. I Highly Reccomend Reading This Book! The explanations are wonderfully simple, while taking the reader through the complexities of LEGO and Technic geometry, gearing, tourque (and how to control it properly) and more. Even if you don't plan to build a robot, whether you are young or 'older', I promise you will learn plenty, and enjoy (re)learning about physics and LEGO!

I originally planned to use a Mindstorms unit to animate some 'shop machines' in the roundhouse. But after reading The Book, I was ready to take on this new challenge. I started by tearing out one quarter of the support wall of the pit, so that I could pass a technic axle through it, but also so that I could strengthen the area on both sides of that pass-through, to prevent damage if something went wrong (even though I was designing to prevent damage).

With the turntable track lowered, I needed to redesign the track suppport structure. I moved to a larger (red) basic gear, and I put a 2x2 yellow tile at four points under the edge of the gear, to help reduce any rocking in the gear. The next gear (yellow) was still too close to the track support for me to couple it to a newer technic gear, so I put a third transfer gear in. I put a plate across the top of the fisrt transfer gear, to help 'take the slop out', and make sure that it engages nicely with its neighbors.

I put a large technic gear on top of the second transfer gear. In order to reduce lateral torque in this gear (a weak point in my earlier efforts), I decided to try counter-rotating worm gears. By pushing equally on both side, in opposite directions, this should reduce the torque, and also spread the torque across two parts of the technic gear. This required putting supports on both ends of both long axles that support the worm gears, as well as using parts to keep the worm gears where they would do the most good.

In order to turn the two worm gears in opposite directions, I needed to use two gears between them, and I needed to make sure their speeds were still matched. I used a clutch gear here to help prevent torque damage, and a small (8-T) gear to couple the second worm gear-axle...but these sizes required using the 1x1 technic hole-through-brick for the two intermediary gears. I used a universal joint to couple the clutch gear to the axle that would pass through the pit wall, more for the look than for the effect, since the transfer would be in a straight line.

I had to modify the pit wall to allow for one gear to spin freely, but the tile above hides the cavity. (The pit wall is three bricks tall, with a layer of tiles on the top.) I also used the 1x1 hole-through-brick parts in the wall, to pass the drive axle through. I should also mention that these gears all needed a 1-plate spacer below the bricks to line them up properly with the transfer I needed to use plates to vertically adjust the pass through of the pit wall as well.

The motor was designd to slide into a docking support outside the pit wall, in case I ever needed to replace a damaged motor. (Another tip from the book!) This also helps control torque in the motor from tearing things apart if the gears bind. I finished putting the tiles back on the pit wall, connected a 9-volt battery box, and took it for a spin. It worked!

I built a 2-brick-tall lattice to go under the large grey turntable base, and I stuck it to the wooden base of the turntable hole in the table. I rested the turntable base plate on the lattice, and put the screws back in...but the motor was too tall! It now sat partially under the wooden table top, and the power connector was pushing the back of the turntable baseplate down! I marked where the motor would be (marking the top of the table), and removed the turntable parts.

After some quality time with the Dremel tool and a sanding drum (removing one layer of the three that makes up the table, enough to make room for the motor to move around), I tried to assemble it again, but it was still too tall. One more session with the dremel finished the job, and the fit is fine! There is enough friction to be able to adjust the turntable ase so the track can rotate freely, and it should stay lined up for a whole day of action!

Picture are in the camera, and should be posted soon.

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
(The LEGO companies have their own pages. This page is mine. :-)

Copyright 1996-2003, David K. Z. Harris, N6UOW
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