making a low frequency, wide arc, 'spinner'

[Big Bad Bob]

recently I had a task that required a low frequency spin device with a
large diameter arc (in this case 4 feet).

To make this happen, I glued a knob that fit a stepper motor "gear" end
onto a dowel rod, counterweighting a much shorter end with bolt + nuts +
iron wire wrapped around it and a lot of hot glue. The nuts actually
"screw onto" the wood, sorta self-tapping it in the process. hot glue
to keep a double-nut in place, then I can screw a bolt onto the butt-end
with more nuts that adjust the counterbalance.

Then, with a balanced armature, you can run a modified version of
Adafruit's motor controller board code on an Arduino, with their motor
controller board and a stepper that came with "the kit" a few years ago.

Steppers can easily give you a nice precise continuous low frequency
motion if you set them up to do that, but they don't have a lot of
torque. So you must carefully balance the arm, then give it a 'hand
spin' until it starts to go on its own. Once going, it continues as
long as there's power, in a nice precise timed arc.

So now I am able to spin "something" in a 4 foot diameter arc, at a
"fractional Hz" speed, easily adjusted, and consistent over a long
period of time.

[you could actually build a giant clock this way, come to think of it,
at least for the sweep second hand - the others would have to be gear
driven off of it]