Lazy Susan Train

Revised 02-05-07

Recently Keith Baggus, from the Pittsburgh Garden Railway Society, described a "gimmick" train layout that he had seen.  It was a train running around a circular track on a lazy Susan.  Since the table was tilted it would spin as the train ran uphill.

This seemed to be an interesting project that could be used for PGRS train layouts at train shows and community events.  What follows is a description of   this project.

Video of first test in MPG format

Same video in AVI format

Right click the image below to play or loop.

 

The Platform:

The smallest readily available track size for G scale is LGB 1100 which is advertised as being 4' diameter.  Unfortunately it requires more like a 51" circle that cannot be easily cut from a 4 x 8 sheet of plywood.

The platform was made from 1/2" plywood.  All of the splices and joints that were needed to make a 51" circle were designed to be balanced in weight so that the table would spin evenly.

Bearings - First Try:

The first test used an old bicycle wheel (with a genuine Campagnolo hub!).  This was screwed to the bottom of the table and mounted to a 2" X 2" board.

This worked satisfactorily with the addition of a single support wheel at the edge of the board.  See the video for pictures of this setup.

Bearings - Second Try:

There is some possibility of writing an article about this project and the bicycle wheel method might not be easily replicated.  For this reason I rebuilt the support system using more off-the-shelf parts.

The center support is a 1/2" copper pipe end cap.  A 1/4" carriage bolt fits nicely into this cap and spins around with little friction.  It also has the potential to carry power to the turning wheel for track power.

 

There are three outside wheels.  These are cut from 3/8" plywood using a 2" hole saw.  The wheels are supported by two brass sleeves that fit inside each other providing a smooth rolling support.

The three outside wheels and the center support are held together in proper orientation with two pieces of wood.

In this photo you can see the carriage bolt in the middle of the center support that is made of plastic pipe.

These views from underneath show the contact points that support the table.

Power to the Table:

Providing power to a moving table is problematic, at best.  One needs to provide two sets of contacts, one for each terminal from the power supply.  In addition these contacts need to be reliable and not lose their connection, even for an instant, as the table spins.

The first tests were with battery operated engines.  They proved that the table would spin but track power needed to be provided so that engines could run continuously for 6-10 hours at a train show.

The first track power system used the bicycle wheel's hub for one pole and a set of slip rings on the 2" X 2" support for the other.  While this worked it was, again, made of unusual parts and I needed to make a power transfer device from more traditional parts.

 
Casters

The wood casters were replaced by 2" casters purchased from Harbor Freight.  They were mounted securely to the three legs of the support and adjusted so that only two of them and the center support would be in contact with the table at any one time.  This seems to give the least friction to the system.

Electrical Pickups

The carriage bolt and 1/2" pipe cap work well for one of the two needed electrical connections.  The next design for the second contact involves placing a brass ring around the plastic pipe cap at the top of the center support. 

A small butane torch was used to solder the joint that makes the ring.  It was held in place by two wires wrapped around its circumference.

Here the ring is test fitted onto the plastic end cap.

The contacts that rub against this ring were mounted on the inside of a larger plastic cap.  Even though this arrangement worked well it was difficult to align the internal contacts when the table was placed onto the center support.  For this reason the ring was moved so that external contacts could be used.

Here you can see the ring on the outside of the black cap.  Note that the center contact is filled with black, conductive grease.

The outer contacts soldered to the ring on the white end cap.  The ring has been moved to the bottom of the cap so that the contacts can rub against the ring on the black cap.

Automatic Tilt Mechanism

In order to make the whole system more automated a screw drive angle adjuster was added.  It uses a motor with a gear head and a threaded rod to slowly lift one end of the support system changing the table's angle.

Note the contacts at the top of the center support in the left center.

 

Bearing Improvement

The center support riding on the head of a carriage bolt worked well but I knew that it could be improved. 

A 1/4" acorn nut and a copper washer work much better.

 

Three Points of Contact,  Not Four!

Experimentation with the three casters and the center support lead me to discover that the table spun much more easily when only the center contact and two of the three casters were supporting the table.  To facilitate this adjustment the center support was changed to incorporate a threaded pipe section.  This can easily be rotated a bit to fine tune the height of the center support so that a small space is maintained between the table and one of the casters.

Motor Modification & Limit Switches

The motor shown above works well when lifting and lowering the platform but, even when run at 20+ volts, takes nearly 10 minutes to lift the table to a 10 degree angle.  Another motor with a different gearing ratio was installed.  It raises and lowers the table much faster as the shaft rotates more than 8 times as quickly.

In addition limit switches were installed to stop the motor when the upper and lower points are reached.

The lower limit switch stops the table when it is horizontal.  Note the diode between the common and normally closed contacts.  This stops the motor when it is rotating so that the table is being lowered.  When the polarity of the voltage changes so that the motor turns the opposite way the diode conducts and allows the motor to work even with the switch thrown.

The upper limit switch is also wired with a diode.  It is tripped by a rotating circle of Plexiglas that is attached to the threaded rod.  Attaching it to the rod allows the upper limit to be easily adjusted by moving the disk.

 

 

 

Wiring Schematic

Hollow Core Doors for Platform

Two hollow core doors (36" x 79") were purchased from a surplus building supplies center for $5.00 each

Arcs were drawn on each for a rough cut - these were several inches larger than what was planned for the finished platform.

The rough cut was made 2" beyond the arc that was drawn above.

Clamps kept the pieces from falling apart prematurely.

Carriage bolts were used to join the two halves.  I drilled for four but only needed two.

Nuts and washers pulled the pieces together nicely

The 1/2 circles were clamped level...

and the bubble level on the drill helped to keeps the carriage bolt holes straight.

Foam gap filler was used to strengthen the open edges in the hollow core.

Tape was used to keep splintering to a minimum for the final cut.

The finished unit weighs in at 21 lbs 2 ounces - several pounds less than the plywood unit.