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