Mechanical gates

Question:

I am searching for a diagram of working pulley system using counter weights to open outdoor gates. No batteries, no electricity. I've seen them on Southern Plantations but have been unsuccessful finding one in working condition. There is a long arm attached to a pulley that is weighted and somehow attached to the gate. As you approach the gate you pull down the long lever...the gate opens...you drive through... on the other side the other long arm is there for you to pull down to close the gate...Any suggestions or ideas??

Answer:

Which way have the gates got to open? Normally, slide sideways or may they swing or lift upwards?
However a few thoughts.

If we think of gates opening normally.
You will need a rope from the edge of the gate to some point at the side of the track. From here the rope would pass round a pulley to the end of your long lever. The free end of the lever needs a counterbalance weight so that the gate is not too difficult to open when the lever is pulled down. A similar arrangement is needed the other side of the gate to shut it.
Using a pulley system in reverse will enable you to move the gate a long way while only pulling a small distance. The disadvantage of this method is that the effort on the pulley system will be larger than the load.

Another point to consider is that the further from the gate the rope passes round the pulley at the edge of the track the better (within reason) as the vector nature of the force in the rope will make it more difficult to open the gate if the rope is too close. You need to slide the counterbalance out to make it easier to open but then slide it back as you pass through the gate to make it easier to close from the other side.

A sketch of the arrangement is shown below.