a cool wave pendulum.
the pendulum has adjustable length and is easy to print and assemble.
to start just move the base sideways in one short stroke about 5 cm or 2 inch.
there are also files for wall mounting witch is easier to start and takes less room.

wire length should be [in mm]:
388
344
307
27.5
24.8
22.5
20.5
18.8
17.3
15.9
14.7
13.6
12.7