It is possible to to drive a tiller using a winch drive. I have success with this using a 1 inch pipe mounted to a windshield wiper motor. A line is wrapped around this pipe 5 turns, and connected to the tiller.
The alignment of the pipe is critical to ensure the line does not walk to the ends.
The advantages over tillerpilots or linear actuators:
use windshield wiper motors from cars, available for very cheap. These motors also have two speeds.
easily adjust the gain by using different size pipe (recommend 1 inch or smaller diameter)
reuse existing line connections from windvane
testing shows this is more efficient than using a tillerpilot
The disadvantages:
Slack in the lines gives more play in the system
More work to connect/disconnect lines than lift tillerpilot from pin
More involved mounting to the boat
lines across cockpit