I think the Blue Ribbon for Best Gravity Powered Gate Opener should go to Alvin E Gandy for
his ingenious system that can still be seen in some parts of Texas and
New Mexico.
The patent was issued in the
1960's and might be a good starting point for someone who wants to make
a more simplified version. A solar powered electric opener would be
easier, but only last as long as the life of the battery and motor
before it would need to be fixed. This mechanical beauty might still be
functional a hundred years from now with some periodic lubrication.
Image credit goes to Google
Patents and Michael Lubke.
Temple
Grandin human powered gate opener.
Unpowered
gate opening part 2.