PCB Coil Motors

The question

Can a stator etched directly into a four-layer board produce enough torque to be useful at small scale?

Where it stands

It spins. Measured torque is roughly an order of magnitude below a wound motor of the same diameter, which is the expected result and not a surprise. The interesting finding is thermal: copper in a board sinks heat far better than a wound coil, so continuous current density can run higher than predicted.