Points Control For

The New Layout

 

Note that the smaller pictures can be enlarged by clicking on the images.

Peco motor in position on the point

 

Introduction:

The original loft layout used manually operated points, but I plan to use remotely controlled turn-outs on the new design. This page describes the process followed to decide upon the techniques to be used and the components to be incorporated. 

Key requirements are identified, then the issues are considered as follows:

1. Choice of point motors (with evaluation of preferred solution).

2. Operating circuit (using capacitor discharge unit to protect the point motors)

3. Control panel (including a solution for the indicator LEDs)

 

Key Point Motor Requirements

The track and points to be controlled are Peco code 75 electrofrog types.

Although the train control system is exclusively DCC, the points will NOT be controlled via DCC.

The points will be controlled via 2 or 3 toggle switched mimic control panels, mounted just below the edge of the layout board, in front of the general area to be controlled by each panel. The control panels will incorporate LEDs to show clearly the active train paths. 

The point control will be via fast solenoid motors and not via slow rotary motor and gearbox solutions.

The point motors will also be able to drive auxiliary switches for live frog switching if this is needed for running reliability.

The motors should normally be mounted under the board, with the minimum of board surgery needed to accommodate them.

Computer control is a probable future requirement for a subset of the points.

 

    Point Motors

Point Motor Choice

 1. Peco motors with add-on auxiliary switch

The Peco motors fit directly to the points via twist tabs, under the point slide switch. A significant size rectangular hole (38mm x 23mm) has to be cut in the baseboard to accommodate the switch. An auxiliary switch is available, which can be glued to the underside of the point motor. This can be used to steer power to the frog, which may prove essential for reliable running on Peco code 75 points, which do not have integral "wiping-contacts" as are used in their code 100 points.

Point motor PL-10:  circa £4    Lower current motor PL-10W: circa £5  Auxiliary switch PL-13: circa £2

2. Gaugemaster Seep Point Motors with integrated auxiliary switch.

The Seep motors screw to the underside of the baseboard. The actuator rod passes through a slot or 1cm round hole in the baseboard. The Seep PM1 motor also includes a printed auxiliary changeover switch in the base PCB which could also be used to steer power to the frog.

Point motor with aux switch Seep PM1: circa £4-50

 

Peco Motor and Switch

Seep Motor

 

The Seep PM1 is easier to mount due to the simple 1cm hole that can be drilled through the baseboard in seconds. However care will be needed to screw the motor exactly at the correct angle and with actuator correctly centred. The Seep integrated switch is an attractive feature.

 

Peco motor in position on the point

(The actuator rod is trimmed before use)

 

The Seep motor is screwed to the underside of the baseboard

(which should be imagined above)

 

Switch attached to the base of the Peco motor

Gaugemaster Capacitor Discharge Unit

 

Seep Motor Test:

A Peco large Y point was mounted on half inch chipboard and Track Bed 5mm underlay foam. A Seep PL1 motor was screwed to the underside of the chipboard with self tapping screws. Mounting the motor in exactly the right location proved a little tricky, but this was achieved. The motor was then driven via a Gaugemaster Capacitor discharge unit, using a contact probe on exposed wire ends. The result was impressive completely reliable point switching operations.

Conclusion: Use the Seep motors for phase 1 of the new layout, but design a mounting method that achieves precise location of the motors with respect to the points.

 

 

Seep Motor Mounting Method:

A Jig is required to ensure that the point motor is fitted accurately under the point.  Plan A) is to mark the actuator hole centre through the point slider hole (Sharp pencil through the hole at each point slider rest position, then hole centre is at the halfway point between the two pencil marks). Describe a circle around the centre point just bigger than the drill bit. Drill vertically through the baseboard, using the circle to detect any drill wander. Then fit the underside jig through the hole from below. Align the tab with the track direction then bradawl the underside screw holes using the jig holes. Fit the point motor and check for accuracy.

(Pics to follow)

 

    Point Switching Circuit

 

Operating Circuit for the point motors

Before the advent of the capacitor discharge unit, the 16V AC was applied directly to the relevant point motor coil via a momentary action switch. If applied for too long, the point motor coil was in danger of overheating to the point of destruction. When the capacitor discharge unit was introduced, the switch "on-period" no longer determined the amount of energy applied to the coil. Instead, a safe but adequate charge accumulated by the capacitors is released into the coil, providing a reliable switching action by the solenoid, with virtually no risk of damage to the coil.

Several point motors can share a single capacitor discharge unit, although simultaneous switching of several points will result in unreliable operation if too many points are switched at once. 

Computer control will require additional interface circuitry yet to be defined but the use of a pair of MOSFETS to reproduce the action of the mechanical switch shown above, driven via a USB to analogue convertor may provide a solution.

 

    The Points Control Panel

 

The Control Panels

The control panels consist of a simplified diagram of the tracks controlled in the area concerned. "Centre off" toggle switches are used for each point and 4 LEDs are used to indicate which way the point has been set. A representation of a part of the control panel appears below. (On the real panel, the tracks will be painted as thicker black lines, to make the "off" LEDs less conspicuous.)

 

Circuit for the Indicator LEDs

1. An idea using the DCC track signal

In a DCC layout, High frequency AC appears across the tracks, but in the arrangement described below, the point movement shorts out one LED circuit, leaving the remaining “on” LEDs to indicate the active rail path. The diodes protect the LEDs from reverse voltage breakdown and the resistors determine LED brightness. Electrofrog points are necessary and isolating rail joiners must be used to connect adjacent rail sections to the frog rails. The three additional green LEDs shown in the diagrams above would be permanently on LEDs powered by an independent supply.

A side benefit is that a flickering or on “off LED” indicates poor electrical (and probably mechanical) point contact.

Note: The upper horizontal blue wire in the diagram below corresponds to the frog connection wire fitted to Peco code 75 electrofrog points.

 

 

The indicator switch arrangement shown above was concept tested on a Peco large radius Y Point receiving a DCC supply to the single track end of the point. 1N4001 diodes and 4k7 resistors were used and operation appeared to be completely successful. (See pics below) Only a single LED was used in each circuit path for the test shown below, instead of the twin red and green LEDs shown in the circuit diagrams above.  However, a disadvantage of this technique is that around 6mA of DCC current is required for each point. On a large multi-point layout, this may add up to a significant proportion of the available DCC current!

 

Control Panel indicator circuit test (left path)

Control Panel indicator circuit test (right path)

   

A problem with frog switching due to the Seep point motor auxiliary switch contacts means "A Total Rethink!":

Further experiments have identified that occasionally the change-over switch incorporated in the Seep point motor, very briefly shorts all three switch contacts together as the motor activates. (Due to inadequate clearances on the printed switch tracks).

This makes the switch potentially unsuitable for live frog switching as such a short circuit maybe detected by the DCC controller as a track short, which would result in a controller shut-down, stopping all the trains on a working layout.

To get over this problem, I have decided to use the point switch to activate a "break before make" DPDT relay fitted under each point. One set of relay contacts will be used for live frog switching and the other set will be used to provide LED switching lines to the points control panel from an independent DC Power supply unit. (I've found a source for 12 Volt relays with switch contact current of 2 Amps, for circa £1 plus VAT .... at Rapid Electronics of Colchester. Please see their details in the website links below.)

However, a definite problem with relay frog switching is posed by the parallel operation of the relay contacts and the moving point rails. The relay will only begin to change position when the point motor is halfway through its movement. If the relay contacts do not open before the moving point rails touch the fixed rails at the end of their travel, then again, a momentary short circuit will occur. If the relay switching speed is fast compared to the point track movement, all would be well. If not, then a solution is to use another relay, with the coil powered via isolating diodes, directly from the capacitor discharge unit, in parallel with the point motor coils. The new relay contacts would isolate the switched feed from the original relay, to the frog, while the solenoid was receiving power. The circuit diagram is shown below:

 

 

Revised circuit for frog switching and control panel LEDs, using the new relays:

 

 

Test results for prototype system based on the circuit diagram above:

The circuit was initially built with the points frog wire disconnected from relay 2 and a bi-directional LED detector fitted between the relay 1 frog feed and the points frog wire.  DC was applied to the rails in place of the DCC track feed.  If the conditions for an instantaneous short circuit occurred, the LED detector would briefly receive a DC voltage between the point frog wire and the relay frog feed, causing a visible flash. Sure enough, each time the points were switched, a brief flash was seen on the detector. Next, the detector was connected between the relay 2 frog feed and the points frog wire. This time, no flashes were observed, indicating that the use of the second relay had successfully eliminated the transient switching short circuits.

The circuit was then updated to replace the DC feed to the tracks with the DCC track feed from a Dynamis controller. The detector was removed, and the points frog wire was connected to the relay 2 frog feed (in line with the circuit shown above). The controller was not affected by points switching in any way and continued to provide uninterrupted power while the points were switched. The frog wire was then experimentally wired, instead, directly to the frog feed from relay 1 and the exercise was repeated. Despite the brief short circuit condition during every point switch, the Dynamis controller only detected the short condition in approximately 1 out of 4  switches, when the controller shut down until the reset button was pressed. 

Note: The 12V DC power must be switched on before the DCC controller is activated, to synchronise the relay contacts with the track position.

 

Photos of the Prototype System in action:

Built on a chipboard off-cut, to simulate the final point mounting arrangements, track and control switch plus LEDs are on top.

 

The point motor, (shared) capacitor discharge unit and a new relay and terminal block assembly are mounted on the board underside.

 

The Relay and Terminal Block Assembly:

The circuit Diagram

 

3 Amp Terminal Block, two DPDT relays, a pair of 1 Amp diodes, all mounted on a plasticard base.

Now for phase 1 of the layout, we need 15 more of these!

 

Next?

 

The Points Control Panel:

A simplified track diagram was produced on the computer and printed on to photographic paper. The diagram was then area bonded to a 2mm thick sheet of plasticard. After the glue had dried, holes were drilled to accommodate the points switches and the 2mm "lighthouse" style LEDs used to indicate the points status. The panel was then mounted on to a simple frame made from 25mm square sectioned timber. Finally, terminal block strips were super-glued to the frame, to provide an interface with the rest of the layout wiring.

The Points Control Panel

 

Underside of the points control panel, showing the switches, LEDs and wiring

 

 

Further thoughts related to computer automation on the layout:

The introduction of user friendly software for DCC layout control is making me re-think my original requirement for non-DCC points control.

The selection and switching of a set of points is cumbersome if using a conventional DCC controller. A separate map to identify the point address code is needed and the process of switching a complex sequence of turn-outs requires a lot of concentration.

However, as soon as a computer screen becomes available for this activity, the layout, including points can be displayed graphically. Use of a touch screen would make the process of manual points switching via DCC, just as easy as that provided by the point switch panel described above........However the big plus is that automated points switching by a computer programme becomes an additional option!

Plans appear to be in hand to add locomotive location detectors (based on bar code readers) to the Hornby Rail Master system. With such a feedback system, Rail Master would (I think) do most of what I require.  It works exclusively with the Hornby Elite DCC controller, which looks somewhat less impressive. However, with the user interface now provided by the PC, the Elite can be tucked away in the background and its multi-press function controls are replaced by the PC.   

 

If I switch over to the Hornby system, points decoders would be connected in place of the manual points switches, which together with the LED display would become redundant. However the double relay system used to power the live frogs without short circuiting the track would be retained................. More consideration is required.

 

The saga continues in the points content of the new Computer Automation web page..............................

 

 

 

 

Supplier website links:
Hattons of Liverpool A first rate mail order company for RTR models. Peco points sourced here.
Trains 4 U Peterborough A good (almost local) source of Bachmann and Dapol product. Peco test motors and switch sourced here.
Gaugemaster Layout phase 1 Seep motors and special centre zero toggle switches sourced here.
Bromsgrove Models Capacitor discharge unit and test Seep point motors sourced here.
DCC Supplies Control Panel LEDs probably to be sourced from here.
Rapid Electronics of Colchester Relays and diodes sourced here at very competitive prices, with no minimum order value.

 

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