Point actuation and layout design
Solenoids and manual control
Construction of a multiple deck shelf layout brings the choice of point motor types and how they work into focus. Which type will suit your layout concept? In the first of two articles, the benefits and otherwise of solenoid and manual turnout control is discussed.
THERE is nothing like a new layout project to keep you off the streets and out of the pub, well most of the time! Whether it is a portable layout divided into modules for ease of transportation, such as an exhibition layout; a free-standing home layout or something hanging off the walls, such as the shelf layout concept described in last month’s issue, there are certain choices that have to be made. What track will suit the design? How deep are the baseboards? What control system do you prefer? How much wiring is involved? And, what type of point control system will suit the design?
When designing the shelf layout modules described in the last issue, its position over an existing layout was a factor in deciding some of the points above. Whilst its modular frames are relatively deep, a fixed shelf layout built on flat boards such as proprietary shelving boards will present challenges with turnout actuation.
The same goes for portable layouts and of course, when choosing a control system cost is increasingly a factor, too. Today a single proprietary turnout and a solenoid point machine for ‘OO’ gauge typically costs about £20-£25, depending on the track and motor chosen (A Peco twist lock solenoid motor has a suggested retail price of £13.50). The same is true for ‘N’ gauge, while ‘O’ gauge modellers may pay up to £40 for a turnout, plus the cost of the actuation device.
When going through the exercise of choosing point motors to suit the new shelf layout, several factors come into play which will determine the ideal point motor, including size, visual impact on lower layout levels, ease of maintenance and wiring. Each generic type was examined, despite the preferences of the past, and an old favourite was discounted as part of the exercise in favour of a relatively new design.
Solenoid point motors
The cheapest electric point control systems are solenoids which consist of twin coils which attract a metal armature rod, moving it to and fro depending on the applied power. The action is momentary, requiring a pulse of electricity to energise the coils to
pull the rod across, effectively throwing the points.
The Peco PL-series of solenoids has been popular for years, partly because they can be clipped to the track base of Peco turnouts. Various accessories for polarity change and baseboard mounting are available, adding to its cost. Solenoid motors are also produced by Seep, which have built-in contacts for power switching in some models. Other manufacturers Include Hornby, Gaugemaster and Rails of Sheffield, to mention a few.
While they have a small footprint, 40mm by 24mm for the Peco PL-10, they are tricky to set up and the snapping action of the coils can place some pressure on the delicate points assembly of turnouts. Furthermore, a capacitor discharge unit (CDU) is necessary for to provide sufficient power for solenoids, which can consume a high pulse of current.
Although their small size and ability to be mounted both underneath a baseboard or on top, which might suit a shallow shelf layout, they are considered to be old and obsolete technology by many modellers, especially as their costs have risen to £7-£13 depending on accessories and design.
IN FAVOUR:
■ Relatively low cost.
■ Some proprietary systems allow the motor to be clipped directly to track products (Peco and Hornby).
■ Small footprint and size, which would suit a shelf layout.
■ They may be surface mounted and hidden in scenery with linkages leading to the turnouts.
■ DCC accessory decoders are available for solenoid motors.
■ Can be controlled with diode matrix electronics.
AGAINST:
■ Old technology which has been superseded by more modern designs.
■ Noisy when thrown (very noisy).
■ High current demand which may require additional components such as a capacitor discharge unit (CDU).
■ Throw action can be fierce, placing strain on turnout stretcher bars and rails.
■ Built-in switches in some types have been found to be unreliable in the past.
■ They usually need a large, fixed control panel.
Servos
Relatively new to the hobby are servo motors, which have become quite miniaturised over the last couple of decades, finding favour with builders of radio controlled models. They are different to ordinary motors in that they rotate to a position determined by a control signal. The rotational action is usually through an arm which stops at pre-determined positions which not only makes them attractive for turnout control but other animated features too, such as level crossing gates and barriers.
Servo motors used in model railway applications are small and compact, yet deliver considerable torque for little current consumption. They would fit in the design of a shelf layout or other thin section layout module or baseboard without difficulty. They can be remotely mounted from the turnout, both on top and below the baseboard top with a wire in tube connection or similar or placed underneath the board.
Be aware that they need a control board or DCC accessory decoder together with careful setting up to make them work well, particularly with scenic features that have to stop precisely in the same place, every time. Once set up, servos will stop on the open and closed position every time and also will move at a pre-determined speed and throw which can be adjusted to suit the turnout.
The typical size of a servo motor used in model railway applications is about 12mm by 9mm by 5mm. Cost varies between £12-£15 per turnout, including the control board or DCC decoder (£3-£6 for a servo is typical). Control boards and decoders with more than one output can be bought, which makes the control cost of individual servos lower than buying single output systems. Furthermore, a suitable mount is required.
IN FAVOUR:
■ Small size and mounting footprint.
■ High power and torque for their size.
■ Low current consumption.
■ Open and close stop positions can be determined to suit the application.
■ They are quiet!
■ Relatively low cost per motor.
■ Use of a DCC accessory decoder removes the need for a control panel.
AGAINST:
■ Servos need a control board or DCC accessory decoder.
■ Programming rotation speed and stop positions is tricky.
■ They can be tricky to mount to a baseboard.
■ Care is needed to buy quality motors – there are a lot of cheap ones about.
■ The action is usually rotary which has to be considered when fitting linkages for the linear motion required for turnout control.
■ No built-in switches for polarity change.
Wire-in-tube manual control
The lowest cost option for turnout control is a manual system. If the visual impact of a manual throw is not an issue for your layout fascia design, a simple lever or knob attached to a wirein-tube connection to the turnout will throw turnouts cheaply and reliably. It is often a method preferred for shunting layouts, where the more hands-on approach with localised control is similar to being on the ground with manual point levers.
Brass tube is run to the points from a lever frame or other method of moving the wire in a linear motion within the tube to change the points. They can be as simple as double-pole, double-throw switches with the end of the control wire connected to them. This provides the throw action and polarity change for live crossing vees or frogs. Other methods include wooden knobs and lever frames.
The easiest way of thinking of wire-in-tube control is the way that
the brake cable of a bicycle works – it is the same concept. However there are limitations to this system. Firstly, the run of wire and tube has to be kept as short as possible. The longer the run and the more curves in the tube, the greater the friction. Wire-in-tube cannot cross baseboard joins between modules easily or at all. A method has to be found to support the tube below the baseboards or even on top in the case of a shallow fixed shelf layout.
The cost per turnout can be as little as £2 to about £5 depending on the cost of the switch or lever frame assembly. This type of control may suit compact layouts with a couple of turnouts where the possibility of congestion below the baseboards in much reduced. Furthermore, the wire-in-tube method, which can include synthetic tube with lower resistance than metal, can be linked to point motors such as servos for remote mounting. Whatever tube you would consider to use, the key to wire-in-tube working is to ensure the tube is fixed at one end at least.
The issue of controlling the polarity of power in turnouts with live crossing vees or frogs becomes an issue with some types of manual control. Analogue layouts may have to devise a way to attach a switch to the mechanism such as a soft micro-switch. DCC users can dispense with switches altogether if a polarity change module such as the Gaugemaster DCC80 ‘Auto Frog’ is used instead.
IN FAVOUR:
■ Very low cost per turnout.
■ Perfect for localised control of yards.
■ It is an old but reliable concept for turnout control.
■ Easily assembled from general materials.
■ Perfect for compact layout concepts.
AGAINST:
■ Length of tube is limited.
■ Baseboard joints of portable layouts are a challenge.
■ Friction of the wire within curved tube is increased.
■ A method for polarity change has to be devised.
■ A method for reliably fixing tubes to the layout has to be sought.
■ How will the manual control knobs or levers fit a shelf layout?
In the next issue, the design and use of motorised turnout motors and other actuators will be given careful consideration with regard to their use on minimal section shelf layouts.