Please look at the revised and improved version :http://www.thingiverse.com/thing:1000218
Servo operated decoupler for G scale trains. Designed to fit LGB Stainz. Video:http://youtu.be/BjXNy2pazCk.
Mk3 housing should fit the screws and require slightly less filing of the sides to let the plate move smoothly.
I have uploaded some images of the springs to help. But it's pretty much bend and test!
Experience suggests that the slots in the hook need to be extended to allow more sideways movement of the hook to help with curves. Unfortunately this means the spring needs a complicated shape to ensure it stays supporting the hook at all positions.
The extended lower part of the body is supposed to support the hook when it is down, and stop it hitting the track
. If anyone can design a better joint for the hook I would welcome the help and be very pleased !
This is an improvement to the bowden cable operated version I designed.
It uses the 1.7 g linear servos that are readily available on Ebay / Hobbyking etc. The servo should press fit in the housing. And it will need the top of the servo arm cutting off, just above the second hole.
The screws are 13 mm #4 pan head screws, and the pivot and hook spring are 0.5 mm stainless steel wire. The spring to hold the hook up should have its opposite end slotted in the slot at the base of the housing, so that the "pinion" can rotate easily when the Plate "rack" is pushed forwards by the servo.
The hook is designed to have limited travel downwards, being stopped by the jutting out housing feature. Without this, the hook will flop down and dig into the track when decoupling, with nasty results. I use this with a ZIMO 645, and the video shows an autocouple maneuver, activated automatically on pressing the "couple" button on my controller.
You will need to cut off
Mine certainly needed a small bit of file work to ensure smooth movement before final fitting to the engine. It is best to drill out all the holes, 3 mm for the clearance for the #4 screw, and 5 mm for the head.
I have put in a number of very thin "plates" in the design to help it print where the large clearance holes get smaller as the print layers progress up. Drilling should clear these easily. Without the plates, the holes are really ugly at the transition..