Roundhouse doors may be too close for magnets

It’s been a rainy weekend here in Vancouver – at last!  The kids and I spent a lazy afternoon raking through the Lego.  They’re working on some very inventive cars, and I’m plugging away at mocking up the mechanism for the roundhouse doors.

I foolishly went out into yesterday’s storm to get some magnets at Lee Valley tools.  I returned with their sample pack, plus a few extras to try out, along with a bunch of their little cups.

Again, I was surprised by the amount of magnet that is required to drive the doors through the 1/8″ plywood base.  It takes two of the 1/2″x1/10″ magnets to drive them reliably.  Unfortunately, these are very powerful magnets, and that much power makes them a little unpredictable.  Basically, you have to keep them apart or else they jump together, and good luck getting them apart again.  The yellow vertical piece, for example, helps to keep adjacent doors from interfering with one another.

However, when driving the two sides of the same door, I didn’t find as much success.  With the magnets at the end of the arm, the magnets on each door touch, and the little bevel gears aren’t strong enough to pull them apart.  So, I taped the magnets half-way along the arms’ lengths, and then I was able to open the doors, only to have them slam immediately as soon as I let go of them.  (I didn’t notice that the magnets had reunited when I took the photo)

Through my experiements, I did find that 1/8″ styrene rod is very close to the size of the rods that minifigs can hold.  That means you can use this material to easily interface Lego with the real world.  That, at least, is worth knowing!  However, unless I can keep the doors open, that bit of Lego trivia might be the only positive outcome.


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