Julian Roberts wrote:Is there a convenient but equally reliable way of actuating such a motor from a lever frame?
Well obviously the lever needs some form of electrical switch attached. An SPDT microswitch perhaps, or a home-made on-off contact controlling an SPDT relay.
Given that much, this design is a simple way to drive impulse point-motors, requiring only one capacitor per point-motor.
The capacitor is charged through one motor coil and discharged through the other. It needs a beefy power supply able to deliver the charge current. A 15-volt 50VA transformer and 4 amp bridge rectifier is ideal. This design needs only a SPDT switch, so if a DPDT switch or relay is used the other pole can be used for crossing (frog) polarity switching:
A POINT-MOTOR CIRCUIT
© Martin Wynne
This circuit operates an impulse solenoid point-motor using an ordinary 2-way toggle or slide switch, or relay contacts. The advantage over sprung momentary-contact switches, electric pencils and other devices is that the switch setting indicates the points setting. The switch never breaks any current, so it can be a low-cost switch. The coil inductance limits the make current. (It must be "break-before-make" action, which rules out some types of rotary switch.)
Another advantage of this design is that it allows impulse point-motors to be operated via relays, multipole switches, computer or hard-wired logic, etc.
The only disadvantage is that it needs a separate capacitor for each point motor. Otherwise this circuit is simple, safe and reliable -- it is impossible to burn out the point motor and it will last forever.
After first switching on the power, it is necessary to work the switch once each way to synchronize it with the points.
Do not work the switch rapidly to and fro, as this is likely to lose the synchronization. If this happens work the switch slowly to restore sync.
The capacitor can be at the panel end next to the switch, or on the baseboard next to the point-motor. It needs to be a few thousand uF or so, rated at least 30 volts -- a suitable common size is a 4700uF 35V high-ripple-current capacitor, which costs typically around £1.25 each: https://www.rapidonline.com/Suntan-TS13 ... 8?IncVat=1 https://www.rapidonline.com/Catalogue/P ... Id=11-3106
Some trial and error of capacitor size with specific point-motors may be needed, and a smaller lower-cost capacitor may be adequate in many cases. The power supply must be DC (usually rectified AC), and the capacitor must be connected the right way round, as shown.
N.B. after switching off the power, the capacitor may remain in the charged condition. For safety if the layout is to be moved, stored, etc., work the switch once each way after switching off.