All the points on the railway are mechanically operated by solenoid point motors which are operated remotely by push buttons on the control panels.
For many years power was supplied to the solenoid motors from Capacitor Discharge Units (CDUs) which, when triggered, provided a powerful momentary pulse capable of changing two or three points at once. This simple but effective method had one drawback: to set a route the operator had to crawl under various baseboards to reach the control panels of all the stations that a train would pass through. In 2011 it was decided to upgrade the control systems by installing the MERG CBUS layout control system developed by MERG (the Model Electronic Railway Group).
This is a networked modular system comprising of input and output modules communicating via a pair of wires. Commands are transmitted across the network and modules can be taught to respond in different ways, such as operating points, signals, lights and LEDs, as well as providing feedback such as point position and track occupancy. A USB module enables a connected computer to send and receive data, permitting software programs to run as virtual control panels or automate the layout.
CBUS module map showing layout of network
For the operation of points two types of module are required: a CAN_ACE3 to encode the button presses from a control panel, and a CAN_ACC4 to independantly control up to four solenoid point motors. The CAN_ACC4 is a CDU which can interpret up to thirty two custom messages and change any or all of the attached point motors. One of the many properties of the CBUS system is that one message can make a number of CAN_ACC4 modules respond: in other words, pressing one button can set an entire route by changing multiple points.
A CANACE4 CBUS module, for operating point motors.
Replacing the legacy wiring with the CBUS system involved the removal of the existing point wiring, the installation of a CAN_ACE3 module at each control panel and installation of twenty three CAN_ACC4 modules near the points. The modules are then linked together with a two wire data cable, provided with a power supply and programmed from a computer.
Every powered point on the railway is controllable from either its local control panel or from a computer (or tablet) connected to the CBUS network. Further developments will add feedback confirming the position of the points and track occupancy.