Small motor (P<10W) with high torque
The commercial gimbals work like this:

They have no gearbox, they're a BLDC motor in direct drive. The motors work the same way as a regular BLDC, but they have ultra low kv. The motors are driven open loop, similar to a stepper motor, since they're spinning too slow for the back-emf method that is normally used. And here's the important part: they don't actually have much torque! They depend on the load being well balanced to reduce the torque requirement.

Edit: Deleted some math, as it was incorrect.