Saturday, August 09, 2014

Roundhouse Doors

The door linkage as it came with the kit. The right-hand side clips
into a special bumper that would be inserted at the end of each stall.
The hook on the left-hand side attaches to the door.
The Faller kit for the roundhouse comes with a spring-loaded mechanism to open and close the roundhouse doors. The doors to an empty stall are open. When a locomotive pushes against the lever in the rear, it closes the doors behind it. Neat and simple. ... However, there are a few things that bug me about this. The speed of doors closing is controlled by the speed of the locomotive, and in order for this to work, the locomotive basically runs into the roundhouse building. The speed of doors opening is controlled by the springs in the mechanism and how quickly the locomotive pulls back from the bumper. Finally, there's no way to have the doors of an empty stall closed.
The linkage after I was done with it. Note the zig-zag strain-relief.

Honestly, none of these issues are fatal, but I went into geek mode anyways. I figured this should be solvable by using a very small RC servo.

First off I modified the linkage to the doors to be straight, with a zig-zag to act as strain-relief, and shortened it to the length of the stall.

Next, I experimented with placement of the servo, as well as how much movement the doors need. I tried to find a good balance between the fairly small distance the linkage needs to move to open the doors and maximizing the angle the servo needs to turn to make the arm travel the needed distance. The larger the turning angle, the more fine-grained I can control servo movement and end-points, thus get a convincing effect. I drilled out the hole on the servo actuator arm so that it is big enough to hold the ends of both linkage wires.

Finally, I built a frame from wood and hardboard to mount the servo securely in place and at the right height.

Doors are closed

What this looks like from the inside.

And now the doors have been opened.
Now I just need to connect this to the servo controller to ensure it works as intended. The servo frame needs some more work to be a little bit less obvious in the roundhouse windows.

After I was done with this proof of concept, I went back to building up the ground around the roundhouse. In the last couple days I added styrene strips to cover the ties in all the places that require it, and now moved on to cover the areas between the tracks.

Pascal asked me today how workers will enter the roundhouse. "They don't come through the engine doors, do they?" - Huh! ... Yeah, he's right, this roundhouse has no other doors, and one version of this kit is sold with an additional building that houses the maintenance office, the water tower, the shop ... and has people doors.

I was already planning to add a lean-on extension in the rear-right corner of the building to act as the local machine shop, so that will also provide at least some more doors. Maybe I'll add another basic door in the side-wall for more effect.


bracz said...

I've seen a number of articles in magazines for this. They typically mount the servos "in the attic" -- that is, under the roof instead of at the end of the stall. That automatically solves the problem of visible servos, plus it does not shorten your available track length.

Bernhard Beck said...

I'm not too concerned about loosing stall length, since the mechanism that came with the kit is mounted in the same location. I don't like the fairly massive appearance of the wood support construction, and I'll most likely end up building a support structure from styrene sheet under the roof at the end of the stall. The servo will need to remain removable for servicing.

Now that the ground around the roundhouse is paved, I can come back to this project, along with detailing inside the roundhouse. It's obviously way too clean and neat.
The bottoms of the stall doors need to be shaved off a little bit, and I will need to fine tune the linkage some more.

Bernhard Beck said...

By the way, and updated view of this is described in a later post: