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.

The third model in the EM1 kit was particularly cool to build as it is the first model where the electric circuit is controlled by a mechanical component. It starts with a wheel hub whose rotation is driven by a motor. The wings on the hub are used as a cam to cyclically push a lever down and then release it; it reminds me a bit of a trip-hammer .

Building the second model was a smoother process; I suspect a key reason was knowing from the start that a certain amount of improvisation was part of the process. I’m learning that, in the absence of specifics or mechanical constraints, I tend to err on the side of longer metal rods which gives some extra room for adjustment.