Way back in November I referred to my inability to correctly set the double slip without the aid of an illuminated mimic diagram and that I had accordingly decided that the point control must be electrical because my hand operated point units would not readily adapt to driving another limit switch to feed the mimic lamps.

My S4 layout, 'Bowton's Yard' uses Tortoise point operators and these offer a simple circuit to light up LEDs to show the point setting. However 'Wheegram Sidings' is a minimal space layout, and there is in sufficient space below baseboard to mount a Tortoise. It proved too, that they would not hide behind the back-scene.

I find solenoid point motors to be much too quick acting and also much too aggressive on the turn-out blades, so these too were rejected.

For some time I have been intrigued by the use of servo motors as point operators but, although being a retired electrical engineer, my knowledge of electronics in general and servo motors in particular is virtually non-existent.

Luckily friends at Manchester MRS and MERG have spent some time on this subject and there is now readily available via MERG, not only servo motors but a kit of electronic bits and pieces for any electronically-challenged person to build up into a printed circuit board that will control up to four servo motors. More complete information can be found at http://www.merg.org.uk.

‘Wheegram’ has only four points, well two points and a double slip actually, but that’s four point operators needed. The MERG kit will drive four servos, so I was faced with making only one pc board and this proved to be much easier than I had anticipated. The down-loads from MERG’s web page were most helpful and easy to follow.

The ‘Quad Servo Driver’ pc board needs an electrical supply of either 12V dc or 9V ac to two of its terminals. Four sockets connect one to each servo, a common terminal provides a feed to your point switches and the output from these switches feed into four further terminals on the pc board. You need to provide the point switches, which are simple single pole on/off type.

My point switches are mounted below the mimic diagram, (like point levers in a signal cabin!) but are actually double pole, double throw (also known as double pole change-over switches). I wanted the second pole as change-over contacts because these were to switch the LEDs on the mimic. I would advise that triple pole c/o switches are a better bet, using the third pole to switch the turn-outs’ crossing (frog) polarity. In my case the layout had already been wired to industrial quality limit switches to serve that purpose and I did not wish to take time to modify existing wiring.

Another MERG kit allows you to build a servo setting box which is used to set the speed and amount of movement of each servo, this data then being retained in the ‘Quad Servo Driver’s memory, so that the setting box is only used once! I was able to borrow a setting box of a fellow Manchester MRS member (thanks Les) but the setting can be done using a PC or laptop and a program down-loadable from the MERG web site. It all turned out to be much easier than I had anticipated.

The following pictures show a side view and an over-head view of one of my servo turn-out operators:

In the side view can be seen the end of a slider unit made from 'Plastruct' square tubing and it is just possible to make out the spring wire lever which is driven by the servo and which inturn drives the slider. The limit switch can also be seen (with the red and the yellow wires); this is also driven directly from the servo's lever. In the back ground you can see the rear view of the mimic panel and all its wiring. Also showing clearly are the phosphor-bronze clips that both electrically and mechanically connect the train cassettes to the track.

The view from above gives a different perspective of the same things.

The next two views are of the mimic panel. One shows the layout in its folded-ready-for-transport or storage mode and illustrates how the control or mimic panel is built in as part of the layout structure. The next is an operators view of the panel. The DPDT switches are below the mimic just as would be the levers in a signal cabin. The route setting is shown by a series of illuminated, green LEDs which are switched on or off, along with the servo motor, by the switches (or point levers). Note the colour coding of the two DIN sockets, one feeds the panel with 12v dc for the mimic LEDs and 16vac for the controller or regulator. The second is the socket for the controller. The un-labeled push-button in the top right-hand was an afterthought and will be the subject of a future entry