More on driving doors

A couple of weeks ago, when introducing my clinic on the Cricut, my friend Mark Dance claimed that if there is a more complicated way to do something, I will surely attempt to do it. Apparently he knows me pretty well.  I don’t know if that is altogether my choice, but the philosophy behind Pembroke does seem to be pulling me down some rarely trodden pathways.

I see opening the roundhouse doors and closing them at the end of the day as book ends for an operating session.  So, they must operate, if possible via a hidden mechanism.

Now, I’ve seen motors driving doors before, and it is tempting to start learning about servos to do the same. However, Pembroke represents a time when labour was cheap and automation was not.  In 1905, motors didn’t open doors, people did.  So, I am avoiding motors, if I can.

That same Mark Dance suggested a cunning mechanism that utilized a sliding drive rod, pushing alternate crown gears against on another.  This has the neat benefit of halving the number of knobs on the fascia, but at the expense of a natural motion for opening a door.   You pull or push a door; you don’t twist it.

I tested Mark’s design with Lego and discovered that it has another characteristic that I would like to improve upon: the motion is too abrupt.  A quarter twiddle at the fascia results in a fully open door above the baseboard. Now I may be able to add stops to keep the model from tearing itself apart, but the motion is not what I want to see.

Either the movement at the fascia needs to be bigger, or the mechanism needs to dampen it.  I thought for a while about gear reductions, which would make the input motion larger.  However all such mechanisms require a bunch of space under the door, or a further connection to transpose the 1/4 turn from a location where there is space.

So, I  abandoned that line of thinking in favour of resistance in the linkage.  But friction tends to give way suddenly, yielding jerky motion. Not the smooth behaviour of a huge 7×17 foot door.  Which brought me to the idea of air dampening, and finally a lossy pneumatic mechanism.  It sounds sufficiently complex to make Mark happy, but whether I can get the parts at a price I’m willing to pay is a bit of a question. I found small pneumatic cylinders for as little as $10, but that’s still $120 to drive the doors on this little roundhouse.

So does anyone know of a source for very light-duty, inexpensive pneumatic systems that I could experiment with?


13 thoughts on “More on driving doors

  1. Rene:

    1st, I hope that the shorter days and cold weather do not dampen you cycling commutes. Lots of rain here and very dark but I still go. Dumb as a post, I guess.

    2nd, pneumatic? You are a glutton for punishement. I bought a bunch of small (really small) pager motors for about ten cents each and hope to make them move slow and jerky with an Arduino. If you are hell bent on a tactile experience then an encoder could simulate opening and closing the door while making the actual mechanism electrical (read small) and still torture you with programming in C++.

    Lastly, I have been exploring Fusion360 by Autodesk. This is a free modeling softeware that does a better job than Sketchup and OneShape. Since I was raised on AutoCad, it appeals to me as the nominclature is similar. Check it out and you may find this cloud based program worth exploring.

    Neil Erickson
    ps: My Cricut is gathering dust! Need more time in my days!

  2. I like the manual labour rationale. I really like the need to feel like you’re exerting an equal amount of effort at the control panel as it would take to swing a massive wooden door open – perhaps fiddling a tiny knob a quarter turn isn’t enough.

    If you are using the opening and closing of the engine house doors than could you use this activity to actually turn the layout’s control system on and off too? As the doors open to the engine shed, the DCC system comes alive and the sound decoder on the engines starts cycling through its start-up.


    1. Someone with more steam experience ought to be able to tell us when they opened the doors. However, I do believe that starting a steam locomotive takes a long time, even from a banked fire. So you might start raising steam and while you’re waiting for that to come up, you would wipe down the engine, oil and inspect the running gear and open the doors.

  3. If you want to simulate the mass of the doors Rene what about using flywheels in series with each door attached to the door axle beneath the layout? Then push/pull rods with the appropriate lever arm to give you the throw you want at each end.

    Btw: I have used disposable syringes for projects in the past and they wear out and exhibit lots of stiction. I wouldn’t recommend them.

  4. Sasting the doors in lead might help give “heft” to the door movement as well as flywheels. Should be relatively easy to simulate the feel with Lego.


  5. Lego makes pneumatic pistons that are hand pumped, but it’s a cheap experiment if you have them already. Does your kids have any to experiment with?

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