The fourth model in the EM1 kit is a beam balance scale with a switch mounted on the main upright. This was a nice build, with only few small surprises along the way. At rest, the vertical metal rod presses the switch in, breaking the circuit, and keeping the light turned off.

If the weight on the pan is heavier than the brick built counter-weight, the switch is released, and the lamp turns on. I ended up using a small brass cylinder as a weight, since it was just enough to release the switch.

One of the surprises in the build was getting the vertical metal rod to friction fit in the groove of the brick. The instructions seemed to suggest twisting cord around it and I ended up using some thread which I had lying around. This works; but, I may also be incorrectly translating or misunderstanding the instructions. In any case, I’m sticking by the idea that improvisation is part of the intention.

The second point was cutting the official thread to support the pan. I found that the thread frayed rather easily and I needed to seal the end to prevent that (and be able to tie a knot). I ended up using the same technique I would with paracord – quickly passing the ends through a lighter.

One particularly nice thing about this model is that it puts the see-through nature of the switch component front and center – literally. This is something I particularly like about the early generations of fischertechnik components – they go the extra mile to make mechanisms visible. I think this is a key part of good UX – giving the operator the ability to form accurate mental models of how things will behave.