Semaphore, controlling servo mechanical mounting & connection


Wanting to tap into a fount of related knowledge, I remembered a classroom reality: 'If you need to explain a topic to someone else, you need to understand it yourself.' So, a list of design objectives, constraints, considerations.


  • The servos have a gnarled shaft with 16 steps. With the body and shaft in a given position, an arm can be position in 22.5-degree steps
  • The closes to the servo shaft I can connect is ~5mm
  • A servo has a range of rotation of just under 180 degrees, which varies servo to servo.
  • Although the movement of the control wire will be sinusoidal, I would like to use as much of the rotation of the servo as practical for granularity.
  • The movement of the semaphore control wire is about 3-5mm from RED to GREEN aspect. With YELLOW in between. This is horizontal/RED, 45°/YELLOW and vertical/GREEN. an "Upper quadrant" signals.
  • The controls from the servos attached to one of the two wires coming down the mast of a double signal should be close to the mast center line to reduce ware.
  • Need to have a small circuit board on the servo mounting bracket for a power plug for the semaphore lights.
  • Because locomotives were invented in England, the engineer/driver is on the right side and so are signals with the semaphore arms pointing away from the track.
  • The semaphore masts will need to be installed on top of a short ~1/2" column. because in some cases, the semaphore arms for one track extend over the adjacent track and need to be elevated to clear passing locos.