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.
Step 2: Setup Your Lines and Pulleys
You should now have a planter with two nylon cords supporting it. Thread these through your pulleys above as per the illustration.
The strings coming from the side of the planter farthest from the counterweight go up to the far side pulley, across the ceiling to a near side pulley, and then down to the counterweight. The near side strings go up to their own pulley, and then directly down to the counterweight. (see illustration). Once threaded, use some binder clips to clip the strings on each side together about a foot above the planter, so they are close together from there one up, and therefore less likely to slide off the pulley wheel.
Step 3: Insert Plants
Step 4: Counterweight And..... Hoist Away!
Tie your nylon string to your bucket, and voila! (add or remove sand as necessary).
If this were a piece of software, someone would have patented "bucket of sand used as counterweight" years ago, and you'd have to pay them a royalty to use their amazingly prescient idea (even if they never actually made a bucket of sand!!). But in this case, you are free to use (and even remix!) "bucket of sand" however you wish! w00t! Revel in this great freedom!
Step 5: That's It! (Room for Improvement?)
Room for improvement:
1. Ours doesn't horizontally offset the counterweight from the planter. It'd be nice to have another pulley, maybe 9 inches to the left of the leftmost pulley, through which to run the lines going down to the counterweight. That way the counterweight would be suspended a bit further away from the planter. I think it'd look cooler, and the counterweight wouldn't hit the planter when they pass by one another.
2. Skip the pulleys - maybe thicker nylon cord could slide through a metal eyehook a bit more smoothly, making the pulleys unnecessarily? Dunno - hope somebody tries it.
3. Find a way to tap into your plant's desires, and, when the plants reach consensus that movement is in order, allow them to raise or lower the planter with an electric motor to suit.
4.... or maybe hook up one of those soil dryness testers, and make the planter get lower and lower the drier the soil gets? (And hoist itself back up after it gets watered?) That way the plant brings itself near to you when it needs some attention.... gnarly.
Things and problems with which we fought valiantly: (Because, hey, whenever you build something, it never really comes together the way you initially planned, even if it ends up coming together even cooler than that.)
1. Pulleys - We first got some lame ones from the home despot that had a lot of room between the pulley wheel and frame. The cord could pop off the wheel and then get sucked down into the axle in all the space. Some cheaper smaller ones, mounted on swivels, turned out to be a better solution.
2. Cordage - have plenty of it on hand, rated well above the weight of your planter and counterweight. Otherwise, you end up trying to splice / knot pieces together and it doesn't look as good. It's also kind of hard to tie things while simultaneously holding 25 lbs of plant in the air.