Tony Wright : Remotely Operated Points
Part One - The Over Engineered Solution.
When visiting other Garden Railways, I’ve seen many solutions to the problem of switching points which are remotely located from the operating area. I’ve seen rods, garden canes and the old favourite dashing between other runners to manually operate the point. My line has several such points which are remote from the operating area and not easily accessible, having to dart to change these is a pain, so making them switchable from the operating area would be beneficial.
Solution.
I came to conclusion that using a pneumatic system would be the easiest solution. I looked at a couple of commercially available systems. Both were from the US and both were aimed at 45mm gauge track systems and not what I was looking for. The cost of these systems is high and supply not guaranteed. Looking round in my clutter box I had a number of pneumatic valves and cylinders which could be utilised. The planned system would consist of an air supply, ground frames to control the points and point motors to switch the blades of the points.
Which Cylinder?
There are two types of simple pneumatic cylinder, double acting and single acting. Double acting requires air to move the piston in both directions, put air in one end and the piston moves away, put air in the other end and the piston moves back. Single acting cylinder differs in that while air is needed to move the piston down the cylinder, once the air is released an internal spring returns the piston. Both types will operate our points, but there are advantages to using a single acting cylinder;
a) the cylinder only needs a single air feed pipe from the valve instead of two.
b) the operating valve is simpler and therefore much cheaper.
The cylinders I have chosen are made from external grade aluminium, have a 10mm bore with a 10mm stroke. They can be mounted by a 4mm pivot in the base or bulkhead mounted by a M10 thread on the base or nose, the piston has a M4 threaded end.
Operating Valves.
The two types of cylinders require different valves to operate them. For the double acting cylinders, we need a 5/2 valve (five port, two way), when operated they direct air to either end of the cylinder whilst exhausting the air from the opposite end. This makes the valves more complicated, larger and therefore more expensive. For the single acting cylinder, we need a 3/2 valve (three port, two way), this only needs to admit air to one port and exhaust it in the second position.
Air Supply.
We need some compressed air. There are many small cheap compressors on the market, some of these are not suitable such as tyre inflator types, these run continuously and the air is not regulated. Compressors with a receiver are the best type to use, small ones with 6 litre receivers are common and will also be useful to power an air brush or for use testing steam locos on air. I’ve set my system to run at 3 bar which is a pressure most air brush compressors run at.
Air System.
The compressor needs to be dry and away from the elements. In my system the compressor is in the summer house where it’s under cover and there is a power supply, the compressor I have was supplied with a hose using PCL XF type fittings. As I had a regulator to hand, I Installed this permanently into the summerhouse which connects to the compressor by this hose. This means I can set the system pressure without adjusting the regulator on the compressor and therefore doesn’t need resetting if the compressor is used elsewhere.
Distributors.
The supply from the compressor is by a 6mm nylon air pipe this runs to a distributor; one is provided for each ground frame location. The distributor is made up from ½ BSP stainless steel Tee fittings, mainly because I had these to hand. A 6mm Tee feeds air into the distributor and then feeds the next ground frame down the line. From the distributor 4mm pipes feed supplies the ground frame. The size of the distributor also acts as a mini air receiver storing air for the ground frame if multiple switching’s are carried out in a short space of time.
Foundations
Both the ground frames and the point motors use the same system for mounting. The foundations for the bases consist of two 42mm diameter PVC waste pipes around 400mm long, these are driven into the ground until firm and level. The inside of the pipe is tamped with an old broom handle, then a watery cement mix is poured into the pipe. The grounded bodies base is drilled for two 6mm stainless coach bolts these are secured to the base with nut either side and the base is pushed into the cement with a little agitation to settle the mix and left to set. Once set the base can be removed from the foundation when required by undoing the nut on the top of the base.
Ground Frames.
The ground frame consists of the pneumatic switches which control the points. I have two operating areas so I decided that only two switches were needed at each operating area. To protect these switches, I’ve used Swift Sixteen grounded iron guard van body, these are large enough to house two switches. These bodies have a separate base which is sufficiently thick to be drilled and tapped for mounting the switches and be strong enough to support then when being used. The body is separate and can merely be dropped back over the base to protect the switches when not in use.
The switches are mounted by a bracket bolted to the base and the 4mm pipes come up through holes in the base and connect to the switches by 4mm push fit banjo fittings.
Point Motors.
To house the point motors, I used the small grounded box van bodies from Swift Sixteen, the foundations for mounting these is the same as for the ground frames.
I’ve used differing layouts for the point motors and developed them accordingly:
The Prototype Point Motor has the cylinder fixed on a mounting bracket using the M10 x 1mm pitch thread on the cylinder nose. A guide tube is soldered to the mounting bracket and a stainless-steel welding rod Is connected to the piston rod. Problem with this design is the rodding has to turn through 90 degrees to operate the point. At this point I discovered the range of M2 radio control fixing from Cornwall Model Boats, this includes threaded rodding, clevis’s, rose joints, connectors and bell cranks. I quickly adopted this for my rodding. At the location for the bell crank need to turn the rodding through 90 degrees, a length of 15mm copper pipe was driven into the ground, on top of this an air vent fitting was fitted which had been tapped 6BA to suit the bell crank mounting screw. The point being operated is by PECO, I used a clevis with the pin removed and the hole opened up, this then clips over the pip on the PECO tie bar.
Point Motor Number Two. With this point motor decided to mount the bell crank inside the box van body and have the cylinder directly operate the crank. Because this is a radial motion, I had to mount the cylinder using the 4mm hole in the endcap. This was bushed using a piece of K&S tubing and a M3 bolt used as the pivot pin. Because the cylinder moves 10mm and the point blades only need to move 5 to 6mm I bent the operating wire in a zig zag to prevent the blades becoming damaged by over travel. With this point the PECO tie bar had failed a number of years ago and the tie bar has been replaced but no longer having the over centre spring and therefore needs the point motor to hold the blades in both closed positions.
Point Motor Number Three. This point motor is in a difficult location under a lift up step, due to lack of space I had to locate it away from the point. The cylinder is mounted by a M3 screw and bush in the hole in the cap end. To the piston road a brass plate is fitted which slides on a nickel silver plate bolted to the base. To this plate a copper tube is soldered to guide the point rodding. Either side of the brass plate are two bobbins grub screwed onto the rodding, these can be adjusted to give the correct throw to open and close the switch blades.
Point Motor Number Four. So far, the point motors we have looked at have all been for facing points. I have one point which leads from the steam up area onto the mainline and is trailing. In normal operation switching of this point is done by the locomotive trailing through the point. However occasionally there is a need to reverse back into the steam up road and therefore the point requires to be switched in this direction. When the point motor is not operated and in the returned position the point blades can still be switched by locomotives trailing through them. When the point motor is operated, the point is switched to the road for the steam up bay. This is achieved by a short 2mm rod connected to the point blade tie bar. This rod is inserted into a sleeve which is connected to the point motor. The rod is free to slide in and out of the sleeve when the motor is in released position. When operated the sleeve moves across and the rod bottoms in the sleeve and moves to closed the point blades.
The point motor has a bracket mounting the cylinder with a tube to support the 2mm rod, bobbins on the rod adjust the throw and are actuated by a plate bolted to the piston rod.
October 2021