For those who have a driveway with a gate. Powered, remote control openers are convenient but sometimes troublesome. An aluminum 6'x15' gate swinging on ball bearing hinges, properly installed and leveled moves easily enough for this to work.

This idea is to use the jet of air from an electric leaf blower piped from the hinge side to the latch side and discharged through a slit on the side of a vertical tube(capped) and aimed opposite from the direction the gate is to move.(open) This vertical tube is mounted on a swivel coupler on its bottom and has a tab on its side that contacts an arm on the stop post which turns the tube 180 degrees while a limit switch at the hinged end stops the blower and a gravity latch engages the gate. (close) Said gravity latch has a light weight arm that is tripped to open by the blast of air starting the gate going in the opposite direction. Another latch. tab, and tube rotation setup is on the other end. If the gate is stopped in mid swing it will stall and not damage the gate as some commercial electric openers will do. Limit switches and blower are housed behind the column on the hinge side. Blower is connected by flexible tube to PVC piping fastened to back side of gate or to the tubing of the gate itself in the case of a new vs. a retrofit application. This is not solar/battery but supplied with house current. Various types of propeller/fan arrangements were considered and rejected due to safety or other snags. The same action/reaction effect would work as well using the force of a water stream or the blast from a bank of shotgun shells but would present other problems.
-- cudgel, Nov 09 2015

gravity latch http://www.homedepo...tch-13557/203133716
gravity latch [cudgel, Nov 09 2015]

random, halfbakery