Summary

A Servo mount with sprung drive for G scale PIKO and LGB points (turnouts). The spring mechanism allows the trains to push past "closed" points without derailing.
Video: http://youtu.be/xdbzOc0kWSc

Instructions

Arm 3 has notches where you will need to cut the arm to length before use. Without these extra bits the arm lifts during print.

You will then need to make two springs from 0.6 mm stainless steel spring wire. One is a right angle bend with 12 mm arms to give the spring between arm 1 and arm 2.
The other is a 34 mm long link from the servo to arm 1 of the actuator mechanism, with the ends at right angles. A kink in this arm gives some resilience and makes it easier to adjust. I used the middle hole in the servo arm. Both these need short "z" sections at each end to hold them securely. The photographs should help.

Care is needed with the right angle spring to make sure that the z ends do not foul the body, the ends on this spring, that fits between arm 1 and arm 2 should both face away from the pivot.

I found that sometimes it is necessary to move the spring holes slightly to get best performance. Arm 1 benefits from having the end beveled by file to allow slightly greater (longer) motion. I may update this in a future revision.

Using a servo tester is highly recommended as it can "bed in" the mechanism.
Some parts may need sanding, or the holes opening out with a drill to give best performance. The 1 mm spring mount holes in particular will need drilling.

I used 0.25 mm height and 0.4 mm extruder to build this one.
The servo is a ES08DE digital servo which seems to work well and is inexpensive. There are 3 mm holes in the back servo mount as it was originally screw fixed, but the "slot in" mount seems to work well.
The single bottom screw holds everything together, but a bit of tape on the long edges makes holds it even better (see the video).
All screws are #6*3/8" stainless steel self tapping cap heads (sorry for change in units!).

If you can design a plastic replacement spring please let me know as I used nearly a whole reel of filament trying to make an all plastic version of this before resorting to stainless steel !

Points Servo Drive (Train track)