PMG Relays as Point Motors

(Article originally on the EMRC website, edited for use).

One way of motorising your points is to use old Telecom relays to throw the points. They have been widely used by many clubs and countless individuals .EMRC started using them in 1980, and though we would share the information.

They work by attaching a right angled bracket to the motor. that hold a point over when energised, and the other way when not powered.

They are cheap to make, work well and provide reliable operation. I would say their diavantages are having the relay on for a lomg time, and the mounting of the relay.

The arm is the main modification - this turns the movement of the relay bracket into sideways movement that moves the tiebar of a point.

We usually use old metal coat hanger wire, hollow inside to which we solder in a length of stiff strong wire, MIG welding wire or piano wire have been used with success. Allow more than enough wire to poke through the tiebar - cut off the excess after installing and testing the point.

To attach this to the relay you could use a very HOT soldering iron to attach this bracket(see photo, below left), some people rivet it on , others weld it on (see photo below right)! (depending on the relay arm's materials).

Our club uses the older series motors. We use 100-250 Ohms coils satisfactory on 12-24V DC.

One aspect to think of is the contacts on the relays. The more contacts, the better return pressure you get. you can also use these contacts for electrical switching. Bear in mind as the contacts are mechanical they can be adjusted for throw - and sometime need correction if they are not making/breaking contact the way you wish !

We have found that a relay with only a few contacts will not return properly. Few contacts will not allow for reliable electrical switching. On our exhibition layout Murranbilla, we have coacting relays wired in parrellel. This means the telecom relay will do the physical moving of the point, and the coacting relay does the electrical switching.
There several ways to mount the relay under the point. We used a "S" style bracket on the club layout (see photo above left). On the exhibition layout we have used a electrical conduct saddle, flattened in the middle (see photo on right). Use two screws to hold the motor in place as they do vibrate, even on a permenant layout !

A popular method is to mount the relay vertically. This gived the relay maximum throw and better return characteristics. One can mount the relay horizontally if required.

As with most point motors, drilling a hole to allow the point motor arm to throw is crucial. We usually work out where the point will be, and it's tiebar, then drill a hole. Next the point is installed.

The photo on the left shows the top of an average point used on our layout. It has the tiebar with a hole which the throwrod comes up from the arm and the relay below.

The photo on the right shows the same basic setup with a Shinohara point.

We have trialled ( for our club) a new method of point control on the exhibition layout. It related to full size point operation which have rods to the motor, not a sleeper ! In model form we wished to make the tiebar "dissapear".

Where the tiabar would be we cut a slot. Then silver soldered two stiff wires onto the point blades. Under the baseboard these two wires are soldered to a copper clad sleeper acting as a hidden tiebar ( ensuring this tiebar is insulated as well). We then solder two runner wires to stabilise this tiebar, and finally a small loop of wire to poke the relay arm through.

The relay is the same as discussed above but does not protrude into the layout. Since the arm is under the baseboard, by shortening the arm we get less throw. you may wish to make a higher mount to get this throw back, but remember this maked the relay sit lower under your baseboard ( a problem with portable layouts where you try to keep the depth of a module to a minumum)

Some extra work is required above the baseboard to hide this slot, and the results is a differenty looking point more in keeping with the real thing.

The reddish tiebar seen in these top views are plasic non operational bars. In time they will seem to connect to a hand lever or motor.

The photo on the left shows a double slip done with this system !

Here is another example off another club's layout "Somerton". You can see how similar it is to our motors, Note the extra contacts and the soldered arm.

Also you can see their method of legs attachement - normal water pipe that fits in the socket and held by a bolt. EMRC have the same idea except we use square steel with our legs mounted in the corner.