More Thoughts on Roundhouse Doors

  
I’ve been pondering the roundhouse doors for a couple of days. Earlier this year, I came up with the idea to drive the doors with magnets beneath the layout.  However, the tangle of rods and levers beneath the baseboard was hard to visualize. So today, I thought I would sketch it out. It still looks too complex to work nicely. 

Unless the rods are quite heavy, I can see them twisting and bending, rather than pulling the doors open smoothly. This is similar to a problem I had with driving a couple of turnouts that overhang the window sill. There the solution turned out to be a heavy block of wood, riding in an equally heavy guide. 

Applying the same idea here looks like it could work again. All the push rods turn out to be slabs of 12 mm plywood riding in slots like drawers.  The drawers have holes in the middle to allow the vertical axles of the doors to pass through, and somehow engage with the ends of the levers that move the magnets. 

The knobs to push and pull the drawers can then pass through the fascia and line up perfectly with a plan view of the roundhouse so the doors are easy to identify. 

There are still some details to work out, like how to engage the ends of the magnet levers so that the drawer assembly can be pulled off if anything ever stops working (or to get it working properly in the first place!). Also, I need to sort out some scale hinges. 

However, overall I am much happier with the drawer idea. They simplify the geometry substantially and they should have a nice robust feel to them. 

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11 thoughts on “More Thoughts on Roundhouse Doors

  1. Hi Rene…

    Is it a design objective that each door move independent of the others including its “partner”? if not – and if moving a pair at a time might be acceptable – wouldn’t a scotch yoke mechanism which pivots in a horizontal plane be relatively simple? The operator “knobs” would protrude through and move laterally in slots in the fascia…swing it one way and it closes the pair of doors, swing it the other to open.

    md

    1. Yes, it’s 1905: you have to open one door, secure it so it doesn’t slap against the engine as the engine is exiting the building, then walk across the rails (careful not to trip!) and open and secure the other door. I haven’t thought about how to secure the doors yet, but I think it might be a lift and drop kind of thing, like dropping a stake into a hole.

      1. You could secure the doors with a lightly sprung latch on the drawer slide.

        And in this case a scotch yoke would reduce to your slide idea with the yoke being a rotational actuator and the slide being a transnational one but both basically doing the same thing in similar ways. Benefits of rotation is it is a single degree of freedom and so simpler and less likely to jam. Benefits of translation is no wasted or ancillary motion.

        md

      2. I had to Google scotch yoke, but yes, that is essentially the drawer idea. Now I don’t know what your original idea was!

        I’m thinking the securing might happen with the knob itself: a notch in the pull mechanism engages with a washer or steel strap mounted on the back of the fascia. The intent of securing the doors is to mimic the real thing, not so much to stop the doors from really slapping against the locomotive; there will be loads of friction to stop them!

  2. Are you in danger of over-engineering everything? Could you not simply open them by hand – maybe using a piece of 0.010″ wire, with an L bend at the end, if you have concerns about an 87 times larger than life hand appearing? If you are manually uncoupling, then you already intervene into the scene, so this should be less of a concern.

    Failing that, pivot the doors on an axle passing through the sub roadbed, with a worm wheel on the end. A simple axle with a worm at one end and a handle at the other can be used to rotate the door. You can put stops into the worm wheel to stop it moving too far. There are plenty of cheap plastic gear sets out there which could be used.

    Simon

    1. You’re probably right, Simon: it is over-engineered. A couple of things stop me from the hand of god approach. First of all, I think if I have to reach up to close the doors, I’m less likely to do it. That means that they are mostly open all the time, which defeats the purpose of making them work – added play value. The second is that the doors should be quite thin and delicate, and I figure they’re likely to break the second time someone goes to open them.

      I actually think worm gears would be even more work, but may have to go that way if the mockup doesn’t work as planned.

      Thanks for your ideas!

      Rene’

      1. You know a loooonnnngggg time ago when I was 14 I controlled all the switches on my layout with a level and fishing lien arrangement that I read about in MR in the ’70’s. I’ll attempt to describe it but it will sound more complicated than it was.

        The operator levers were oriented vertically and pivoted back kind of like those old Armstrong bars in junction towers. When you pulled them back they pulled on fishing line which ran through eyelets to get to below the switch. At the switch a piece of music wire ran vertically through a tube attached in the roadbed then bent over and connected to the switches throwbar. A thin brass arm soldered at right angles to the music wire beneath the roadbed was what the fishing wire attached to. Pull on the fishing wire and the music wire rotated moving the switch points. A spring on the other side brass arm provided the return force. A notch in the control panel at the fascia provided something the Armstrong bar could latch in to. They worked great and you could run the fishing wire around corners and over and around each other with no problem. I will send you an old picture which might clarify the front panel.

        md

  3. You could extend the music wire into a cantilevered spring but you may need more throw. Or just wind spring wire around a mandrel in a drill to make one as long/soft as you want. 30 seconds of wrapping and you probably have enough length for all the springs combined.

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