Point Control

23 May 2011

I started motorising my points in the garden using Fulgurex motors with homemade plastic covers. I mounted them on timber outcrops from the edges of my baseboards but they were not easy to locate because of their large footprint. After a while the motors filled with ants and other wildlife and the switches were not making contact properly. I think the contacts had started to corrode. I decided to try Hoffman motors instead.

First impressions were favourable. The Hoffman motors are more compact than the Fulgurex and fairly well enclosed. However by the following year the plastic "ears" used to screw them to my timber supports had sheared off from the main body casing. I don't know if the plastic had degraded over the winter or whether the timber that supported them had expanded and forced them apart.

I designed a new support arrangement using 40mm x 40mm aluminium angle with a crank on the top as shown below.

I installed three like this but one of them overheated when the tiebar got stuck with a twig and stopped the motor moving. The other 2 are still working after more than 2 years.

I cleaned up the Fulgurex motors and used them on the hidden sidings in the garage but I still had problems with reliability.

I am now experimenting with servos using drivers from MERG driven by relays and microswitches on the tiebar driving LEDs on the panel to indicate when it gets stuck. So far I have used standard Peco points. I tried removing the spring on the point on the patio bridge but then had trouble with expansion of the control rod with the heat of the sun so I have readjusted the servos with the spring taking up the final movement.

Thanks to Terry Hackett I now have a MERG Steady State Accessory Decoder installed in my garage. At the moment it is controlling 3 points as an experiment to see if the new setup is more reliable than my LS150 and Fulgurex motors.

One output from the MERG decoder controls a DPDT relay. One pole on the relay drives a servo via the MERG servo4 driver board. The other pole drives another DPDT relay which switches the frog and the track facing the point. This is so that only one hidden siding is live at any one time.

This arrangement is capable of driving 8 points from one decoder and is very cost effective. The second relay would not be required if I was only switching the frog.

The servos were installed as direct replacements for the Fulgurex motors without any change to the linkage. So far I have had no problems at all.

The following two pictures show progress so far on operating one of my loops section points. The black ABS box contains the servo, relay and tell tale microswitches to indicate when the tiebar has completed its travel. I made the black plastic cover because the ABS box lid was not water tight. It has survived the winter like this and so far so good. Since taking the pictures I have completed the installation except for connecting the point frog to the switch on the relay. The relay, switches and servo are working perfectly but the telltale switches are proving a problem. This is currently under investigation.

The relay is operated by a MERG Accessory Decoder in the Loops control panel.

Here is a schematic for my wiring of accessory decoder, local switches and relays. The accessory decoder provides 12vDC for driving the relays but there is not enough power for the Servo4s and servos. A separate 12vDC supply is provided for these.

For normal working the points are controlled using the switches on the panel. When the panel is switched out they are controlled from CTI's CTC panel using the accessory decoder. The second pole on the "switch out" switch is connected to a CTI Sentry so that CTI knows the state of the panel. In an emergency or during maintenance the points can be controlled directly using CTI, a DCC throttle or via JMRI using my iPOD. This is proving really useful.

I have connected the point frog to the relay switch in my latest servo box which is similar to the one shown above. However some time after switching everything on the servo starts to twitch. The twitching stops if I switch off the DCC supply to the track and frog. I think the close proximity of the DCC wires and servo control wires in my servo box may be causing interference. The next step is to try locating the relay in a separate box so that those wires do not come together so closely. Watch this space!

New Approach - 8 May 2013

At some time over winter water got into one of my point control boxes and caused some corrosion on a servo board. It doesn't work properly now!

A bit of lateral thinking produced a new approach which I am in the middle of developing.

I have produced an Accessory Board as shown below.

This includes a MERG Accessory Decoder, two MERG Servo4 drivers and eight relays to control eight points. It is mounted on a piece of Ecosheet recycled plastic and the intention is that it will fold up between the frames of my outdoor baseboard with the electronics facing down. It never gets wet from rain under my boards and the plants growing up each side also protect it from snow. I may need to coat the boards with printed circuit lacquer to stop corrosion from moisture in the air. The hinges allow the board to fold down for maintenance.

I have used my standard wiring practice. That is for each point the Accessory Decoder switches a 12v DC DPDT relay One pole switches the servo driver and the other pole switches the frog. The points to be switched by this board are located in three different power districts so there are three DCC track busses input to the board. There are also four frog outputs and four sets of servo outputs.

Inputs to the MERG boards include the DCC accessory bus, 15v AC to power the Accessory Decoder and 12v DC to power the Servo4 boards. The relays are powered from the decoder.

The remaining wire dangling from the bottom of the board is the 0v connection to the accessory decoder for switching the local control panel in and out as shown in Point Control.

Three wires run to each servo which I plan to mount like this.

Again I have used Ecosheet and the mount will screw to the side of the baseboard. You can just see the hole for the control wire by then servo horn. That will be level with the baseboard top. Hopefully the top sheet is high and wide enough to protect the servo from the weather and experience suggests snow will not reach it. By using a twin horn I can mount two microswitches under the top sheet to detect blade movement when required.