Here is a vine of it: https://vine.co/v/hWDhp0tgw7Z
Step 1: Mounting hardware
So: mount a rail of 80/20, or anything sufficient to carry the load, above where you want your planters. This is where you'll mount your pulleys. Set them up so each horizontal planter has:
1 pulley for each side
1 extra pulley on the side on which you plan to place your counterweight. This will become clearer in the next step....
You can use any pulley that will carry the load - but probably cheap pulleys, that add some friction, will work best. You want the planter to be able to move up and down, but not without friction. A nearly friction-free pulley would force you to adjust the counterweight whenever you changed the weight of the planter (i.e. after watering the plants). Some friction makes thing moveable, but not too easily, so they won't move on their own.