Designed for my father, this servo mount will allow you to switch a Lego train using an arduino or other hobbyist microcontrollers with a small cheap servo and this servo mount.
This design has been based around the "SG90 Micro Servo 9g" which is widely avaliable from a wide range of retailers.
Note that there is a 'left' and 'right' version of the base to be used accordingly with left and right hand switches.
"servoHousingV4Holder" Holds the servo itself, slide the servo into the holder. This is then placed on top of "servoHousingBase". "servoHousingSwitch" is then fitted on the end of the servo's arm to reduce strain on the servo. Clip the whole lot onto the top of your lego switch, keeping the yellow lever attached and positioned in the middle of the "V" shaped part of the servo housing switch part, then add the "servoHousingLid" to finish it all off.
For example code you can check out the following project on Github.
The switch piece has been updated and now has a small hole for the screw supplied with the servo. See servoHousingV2Switch.stl
servoHousingV1Switch.stl is still avaliable if you would still like it without the hole.