On 2005-10-23, wrote:

What do I need (relays? gears?) to have a small electric motor turn on
via a timer, run for the few seconds needed to raise a small (10 x 14
inch) piece of wood via string and pulley (door to a chicken coop),
turn itself off, then turn on again via timer hours later and run in
the opposite direction to lower (close) the door and turn itself off
until it's time to tbe turned on again?

first off you'll need a timer to control run it, a power source for the
motor, a couple of relays to control the direction the motor runs in and
pulleys string and other hardware.

This seems to be on the
principle of a garage door opener, only smaller and opening/closing on
a timer switch instead of a push-button or transmitted signal, right?
Are there systems like this already in existence?

I don't know of any.

a used electric car window mechanism might be a good starting point for a
home-made system.

Bye.
Jasen