My friend Mark Dance has been coming up with all sorts of ideas for mechanisms for Pembroke lately. This week, he sketched an alternative mechanism for opening and closing the roundhouse doors. I’ve reproduced his sketch here, along with my usual ruminations.
Mark’s idea is to use Lego bevel gears on a shaft that can be pushed or pulled to engage the bevel gears for each of the two doors. This way, you still can open one door at a time, which was a design requirement. Springs could return the shaft to a neutral state so both doors are disengaged.
Mark’s design has a couple of very nice features. First, it reduces the number of connections to the fascia down to one per track. This reduction makes the threading of all those control wires much more practical. With six levers in about four inches of fascia height, my earlier ideas were not likely to pan out. Second, I expect there will be a lot less fiddly adjustment: simply center the vertical shafts beneath the door hinges, and the rest should just work.
Next step is to create a proof of concept with Lego and see if we can drive some mockup doors.
Pembroke:87 
The Kragle?! Nooooo!
I’m open to other ideas…
I think the Kragle is only evil if you’re using Lego as it’s intended. If you’re using it for engineering purposes, all bets are off 🙂
I’m thinking perhaps I should make a custom Lego piece that holds a rare earth magnet.