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?