Build an  Automatically Indexing

MODEL RAILROAD TURNTABLE

 

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Started  12/2012,  Last update 2/2013

 

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NORTH RIVER

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The roundhouse and turntable is often the main focus point of a layout. Modelers build their own roundhouses yet few attempt to build their turntable. This is due to several factors but mostly to the complexity and precision required to create a rotating bridge that turns smoothly and lines rails up accurately

 

Unfortunately there are only a relatively few tables on the market today.   One or two small tables are available but are not realistic and do not meet the needs of most modelers.  Most commercial tables of any reasonable size are expensive, hard to find, have few features, and are difficult to use.  Most are positioned by eye which can be a slow and tedious process.  Those that are automatically indexed reliably are rare and expensive.

 

This project is based on a design built 35 years ago.  It takes a new look at an old problem and provides what seem to be a few unique improvements to the situation.  First and foremost, positioning is done optically using a light source and pairs of photo cells.  This principle is used today in precision machines used to manufacture parts to close tolerances measured in millionths of inches.

 

Another huge improvement is the use of a printed circuit board (PCB) for the "slip rings" used to transfer power to the bridge rails instead of depending on the ring rail.  This PCB is also used to replace the various switches usually required to control the power to the approach and stall tracks as well as to provide power to the light source for the positioning system.  This makes operation much easier and less confusing.

 

Other improvements include details in the pit construction not included in  models I have seen including a pocket in the pit wall for the maintenance of the motor and boogies at the bridge ends.  Also modeled is a simulated locking system to keep rails aligned.

 

 

A SHORT HISTORY:

 

The North River railroad runs under a computer controlled block system with a wireless throttles. This concept was developed before DCC became practical with the idea being to allow the train crew to watch the trackside signals, not a control panel.

 

Switches are controlled by trackside switch stands, again so the crew could be near the train at all times. A concession was made to place mini-panels at the table edge for those switches out of reach or near sensitive areas.  These were originally twin-coil solenoid machines but have recently been upgraded to stall motors.

 

The wireless throttles use some of the same technology as DCC with the pulse-power to pure DC transition as the train speeds increase. One additional feature is (3) buttons that send signals to the computer. These were used to initiate and terminate a run as well as to control the turntables. The buttons will still operate this new control system with the addition of buttons in front of the table and with a dedicated controller for each table.

 

The original design incorporated the control of the turntables into the same computer system that ran the block system.  One problem with this was that the block control was "locked out" as the turntables approached their final position.  This new system uses a control system for each table separate from the block system.

 

With time, the rubber parts of the original drive system dried out and ceased to have enough friction to turn the table reliably.  This new system contains a much more dependable drive.

 

           

Bob Van Cleef, mmr
http://www.NorthRiverRailway.net

ravancleef@msn.com

Please visit the main site of the

NORTH RIVER RAILWAY

          

 

 

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Model Railroading is fun in Connecticut.
Bob Van Cleef, MMR

 

      NR_BW          Last update 02/22/2013