Realising a Dream - 21 - Point Control

Choice

I decided to go for large radius Peco Electrofrog points where possible for improved slow speed running of all locos through the pointwork. This is important for a layout built for 1960s freight operation. Insulfrog points are only used as a last resort in scenic areas and extensively in non-scenic areas such as fiddle yards where access was difficult for wiring and train speeds are higher.

Laying points on soft underlay requires more care as opposed to mounting on stiff materials as it is easy to pin them down badly so that the centre is high or low relative to the rail connections. This would affect the ability of locos to pickup power and potentially affect blade movement.

Control

Point control by DCC was not a requirement as I do not intend to let a PC control my railway, that's my fun and I intend to walk around the railway before I become a static fat controller.

Five Scenarios

1) Scenic areas (Electrofrog) my default and preferred method is to use GEM Mercontrol wire in PTFE tube operated by slider switches which also provide frog polarity switching.
Most switches are placed at the edge of the baseboards amongst hedge rows, or on docksides with crates over the switch top.

2) Scenic areas (Electrofrog) with difficult access - point motors by Peco and Maygib with frog polarity switching contacts.

3) Non-scenic areas (Electrofrog), finger from the sky to operate the point, micro-switch operated by one end of the tie bar to change frog polarity.

3) Non-scenic areas (Electrofrog) with difficult access - point motors by Peco, switch module added for polarity changing.

5) Scenic areas (Insulfrog) tight spaces such as docks - finger from the sky to operate the point or electrically operated.

GEM Mercontrol - Options

I did consider using their lever frames and bought some but although the earlier frames were of aluminium plate the later cast alloy ones were disappointingly crude and assembled into banks very poorly.

Positioning multiple lever frames would become quite involved resulting in many cranks and levers like the real thing but it quickly became obvious this was going to be a very long and difficult process to achieve with so many points spread across the marshalling yard alone.

Also how to include polarity switching, well I did experiment by making modified end frames on the plate lever frames to hold a bank of micro-switches but once again positioning many of these modified lever frames with 2 or 3 wires per lever was going to be exacerbate difficulties in assembly, maintenance and updating.

For me using DCC for loco control was as much about avoiding complex switch panels and their inherent difficulties to modify as was realistic train control. This lever frame arrangement was heading towards being a 3 dimensional panel with the complexity and inflexibility centralisation brings. In addition it requires a large quantity of cranks and levers which not only cause added complexity but every link and joint reduces the positive action of a point throw as they are not precision components. Reliable operation will rely heavily on the over centre action of the point spring to ensure a positive snap over occurs, in my experience this cannot be relied upon as points age.

Ultimately I ditched using the Mercontrol lever frames altogether and decided to opt for another approach that I saw online and that was to use simple slider switches with holes drilled in the toggles to through which the Mercontrol wire was attached. The switch contacts are used for polarity changing of the frogs, the current rating of these switches are often fairly low but using double pole switches meant pairing contacts would spread the load.

It must be remembered that if they are switched whilst passing current they will not open simultaneously so the last of the poles to open will take potentially excessive current. However points will only be operated when passing current by error as a loco will be on them at the time, this is also another good reason to limit track current as 5A supply to the track not tripping at e.g. 4.5A would burn out the switch contacts, the approach I take for current limiting is covered in Ref. 21.1.

Installation of the Mercontrol Wire

The general process of connecting points to the switches went like this, the points and adjacent track were only lightly tacked down so they could be gently eased upwards 4-5mm.

1) The foam underlay next to the point tie bar end was cut away. Threading of the Mercontrol wire and its PTFE tubing under the foam was aided by a stiff larger gauge piece of steel wire with a loop on one end that was first fed between foam and baseboard sharp end first from point to board edge leaving the loop just exposed at the point end.



The Mercontrol wire and its PTFE tube was then hooked onto the loop and wrapped with some masking tape to prevent snagging on the underside of the foam sheet. The Mercontrol wire and tube were then pulled to the edge of the board and the hook cut off, leaving the hook of Mercontrol wire dangling over the edge of the board results in get it stuck in my finger like a fish hook, not nice!

2) At both ends the PTFE tube is lightly tacked in place with a lightweight staple gun, hot melt glue is then applied to the staple, tube and baseboard to lock them together. PTFE is difficult to stick to anything hence its used as a non-stick surface on cookware (where PTFE is known more generally as Teflon), but the combination of staple, glue and wood surface holds the tube sufficiently static for reliable and positive point operation. In the image below cutting away foam by the point was not required as the mainline is on a separate section of foam.



3) Connection of the Mercontrol wire at the point was by a simple right angle bend upwards through the centre hole of the point tie bar while gently easing the point away from the board. Once fitted the point was pinned down fully and the excess wire i.e. 1mm above the tie bar was cropped off.

4) The switches were then mounted on the edge of the boards in line with the point they operated, the aim to keep the runs as short and direct as possible. At the switch end a zigzag bend was made in the wire for throw adjustment and then it was bent to pass through a fine hole drilled in the switch toggle and further bent again to partially wrap it around the toggle to anchor it.

The image below shows a pair of switches before the glue was applied, the yellow card is just a background for photographic clarity.



Where necessary flaps were also cut in the foam to help route the wire and tube under the foam and to insert staples. These are easily glued down again and hidden by scenic material later.
Flexure of the tube when operating a point must be avoided otherwise the tube and not the point blades will move when the switch is operated. This is especially the case when the tube path is curved or has a free length greater than about 6 inches (150mm).

5) Power is supplied to the switches by two runs of bare tinned copper wire to the outer switch contact terminals, the centre or common connection would be routed to the frog to be polarity switched. If the point was Insulfrog I left the common connection unconnected. These switches are two pole two way, the parallel terminals are wired together to improve reliability and convenience so they act as a higher current rating single pole two way switch.

The red wires were soldered to the switches first, then the blue to the centre terminals and finally the black wires to the outer terminals, this sequence allows easier access and visibility. The red and black PVC sleeving was added as the tinned copper wire was threaded through the switch terminals to ensure the bare wires did make inadvertent contact between switches.

The next picture shows one side of six switches prior to soldering the tinned copper wire to the terminal eyes. It turns out that the switch action of all the points with respect to the polarity switching of the frogs meant this was possible, I didn't really believe that to be the case hence the red dots on the board edge, but as this was consistent I could wire them in a simple bus fashion.



6) The whole marshalling yard was divided up into areas such that each area's frog wires could have a resistor colour coded tags, from 1 - 8 or more as required and be connected to local tag strips. By wiring in this manner it allows easier updating. If a point was moved or a switch was moved the change was limited to one side or the other of the tag strip. It certainly proved useful whilst deciding whether to use a GEM switch frame or the small slider switch alternative which came along later.

7) Blue wires were then soldered to the switches with tails long enough to reach the tag strip, followed by the second bus wire (black).



8) Once completed the wiring was typically of this form in multiple positions along the marshalling yard site.



Replacement of any failed switches only requires cutting the bus wires say 20mm to one side of a switch, removing the mounting screws, melting the solder joints and pulling them through the terminals. Followed by rethreading through the replacement switch and hooking in an extra length of bus wire to join them up again. The blue wire is simply de-soldered from one and soldered to the replacement. Similarly where points have been removed or new ones inserted such as in recent cement works yard development.

9) The outer supporting strip of wood was fitted to secure the outer edge of the switches and tidy everything up. The gap above the bus wires to be filled with assorted colours reindeer moss as a hedgerow.



Continued below ...

 

Continued from above

Track Mistake #3 - Mercontrol Wire rusts very easily.

Two very effective ways of rusting the wires so they seize in the PTFE tube.

The first method I learned the hard way and meant replacing Mercontrol wire and tubes on over twenty points in the marshalling yard area over a period of a month.

1) Allow diluted PVA and Fairy liquid from fixing ballast to wick up the tube, after a few days the trouble starts, the rust expands the wire and forms a tenacious grip on the tube.
All that can be done is replace the wire and tube.

Reconnecting Mercontrol wire to a ballasted point via the tie is nigh impossible so I attached the replacement wire to the exposed end of the tie by cutting off the vertical spigot and drilling a hole in its place. Not as neat or hidden but lifting a fully ballasted point will result in a broken point to replace, it can be done , I have had to replace a broken point, but it is rather involved and results in destroying the point to minimise damage to adjacent track work.
Now I only apply dry loose ballast near exposed Mercontrol wire.

2) More subtly reindeer moss used as hedge rows covering the wires feeding the switches was moist enough to severely rust the exposed wires over a year, luckily it was more localised and wire brushing off the rust and applying a little WD-40 saved the day.

I have now inserted spacers of foam to keep the moss away from the Mercontrol wire and used non-moss foliage over them and randomly in other places so as not to create an obvious pattern.

Electrically Operated Points

Not much needs to be said about this as it is much simpler except that using capacitor discharge units IMO is a must to give positive switching, I have three of these distributed around the layout, fed by a common mains adapter. This arrangement limits voltage drops in the cables with only one light weight adapter required. Peco point switches were used in all cases and colour coded to match locally placed track plans for the 'signalman'.

Adopting a wire colour coding is useful too, I used grey for the solenoid common, yellow for normal position and purple for operated or diverted so that when the wires approached the switches the orientation was know. Similar to wiring point polarity switching, the wires from the point motors terminate at a nearby terminal block which allows easy removal of a point motor without having to unsolder under the board or from within a bank of switches which are quite densely packed.

I use screw terminal blocks (choc blocks) here instead of soldering for three reasons.

1) Ease of access with just a screwdriver for which they are positioned near the board edge.

2) point motors or their attached switching are more likely to fail than any other component due to their mechanical build.

3) voltages are such that any modest terminal block resistance due to oxides will affect them very little, however the surge currents will notice an ohm or two, but a poorly performing point motor is easily traced.

I prefer not to use terminal blocks for DCC bus wiring, DCC wiring needs to be assembled to a much higher degree of integrity and reliability to avoid difficult to trace issues spoiling ones wrinkly years of training!

I have adopted a signal box type of approach for the switch positions, away from the operator for 'normal' and towards the operator for changing point direction, to divert a train from its normal, often through route.



For each position that a bank of Peco switches was placed I created a diagram with AnyRail which was laminated and placed below the bank of switches. This is the one for the entrance to the South Fiddle Yard, the main (East) yard is to the left with its own diagram. This 'box' South Fiddle Yard West controls the connection to the mainlines on the lower level and the non-scenic turntable.



The black chevrons indicate the 'normal' position of the points when the switch levers are away from the operator. The normal in this case is when the main running lines (red) and the yards lines (yellow) are independently operating.

References

21.1 Realising a Dream - 24 - DCC System - Districts
This is in preparation and a link will be placed here when posted.

Next, DCC System

Discussion always

Jim

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