MEMORY WIRE TURNOUT ACTUATOR

 Version 1.0

Developed by Martin Seekings

Copyright 2002/2003

Figure 1

FIGURE 1

Figure 1 shows the basic construction on a 20cm x 5cm (8" x 2") hardboard base. About 20cm of memory wire is secured in a V shape with bolts and washers to 2 pieces of PC board. The smaller piece at the point of the V has a hole, through which passes a small elastic band which goes around a bolt fixed to the base. This maintains a very light tension to keep the wire from sagging, and will also stretch if the turnout is obstructed when activated. The actuator arm, which has the copper cut through to isolate one end, swivels on another bolt fixed to the base, and a piece of 1/16" brass tubing is soldered into a hole on the end, providing a 3:2 (approx.) mechanical advantage, with a 1/32" wire soldered in the top to pass through the baseboard and tie bar.
Figure 2

FIGURE 2

Figure 2 shows the wiring and mounting spacers attached. A common feed is attached at the point of the V, and voltage fed to one of the two wires soldered to the actuator bar, causing the memory wire on that side to contract and move the actuator pin. When the voltage is removed, the Peco or Hornby turnout over-centre spring holds the points in place. The device needs to be accurately positioned under the baseboard and tensions adjusted to operate the turnout as desired. The memory wire can be adjusted by reducing or increasing the number of turns around the bolt. The wire required costs about €2.60 (£1.80), but since current is only applied momentarily as with a solenoid, no complex voltage or current regulation circuitry is required; a pair of 1.5V batteries will suffice.
Figure 3

FIGURE 3

Figure 3 is a side view, showing the attachment of the elastic band. The bolts, nuts and washers used are size 4-40 American National/UNC (similar to 6 BA or M3 - approx. 3mm).

Memory wire purchased from Pro Rail International

This is my first attempt, and other variations are possible. The actuator bar could be triangular or T-shaped, allowing the device to be attached parallel to the track rather than at right angles. It could alternatively be installed the other way up, attached directly to the baseboard, as long as clearance is provided for the 2 bolts passing through the base.

I would welcome any comments or suggestions on how this turnout actuator might be further improved.
Page composed at 800x600 with Netcape Composer 1 July 2003