Project 26 - Hewish Gates

My original Hewish Gates layout was levelled to make way for my Battledown Flyover layout. I am feeling the loss of what was a delightful scene around the level crossing, particularly the merge of foreground to background, the latter being a photograph of the real location.

Hewish Gates was a compact scene on a larger layout. Whilst I don't have the room for another layout I decided to make a diorama of it that could be embedded in a larger layout if the opportunity arose.

Hewish Gates in reality is located on the main line west of Crewkerne in Somerset. Today it is simply a barrier level crossing with all buildings gone. In its heyday the box not only controlled the level crossing but a long siding and loop west of the box.  

Having revisited the data I have of the prototype I noticed that I arranged the railway cottages to face the road whereas they should face the railway. That will be corrected as will some other anomalies.

For added interest I decided to make the level crossing operational and may add lights to the buildings and level crossing lamps.

First though, how to make the level crossing operational? All the tutorials I found on the web used servo motors and these require control electronics. I did not want this (which is a bit odd since I spent a large part of my career as an electronics designer). I preferred a simpler remote control by manual means. 

This exploded assembly is what I came up with. The principle is rack and pinion gears. The gates are connected to the four corner gears by rods.

At first I had just four gears, two each side, operated by one rack. Since the gates form a square (equal sides) all four gears mesh together except the two nearest the rack would not mesh!

Couple of points to understand for correct operation of the gates is the gears connected to the gates have to turn in opposite directions, which is why we need an even number of gears.

My second attempt was four gears as shown and plus two between them, set furthest from a single rack. Problem is this is not a precision gear design. Sloppy tolerances meant that the gates on one side did not turn a full 90 degrees.

The answer was two racks. Note that the racks need to work in opposite directions to get the gates to open symmetrically. It requires a push on one and a pull on the other. This could be achieved with one lever and another gear between rack rods. However, to avoid the complication and with fear of  mechanical tolerance problems I decided to drive the racks independently.

The rods are quite long, longer than the print bed of my FDM 3D printer which is why extension rods are used. 

Rack travel is limited in one direction by the protrusion on the racks that hit the frame and in the other direction by the rod couplings hitting brackets.

If this was ever embedded in a layout the rods would need to be controlled at the front rather than the side needing a sliding mechanism instead of push pull.

 

This photo shows the size of the diorama and the level crossing location. I have used masking tape flags to represent the gates for testing purposes and yes the method does work.