[GeeTwo]

Let's start with a 7 gal (1617 cu in) charged to 117.6 psig (that's +8atm, selected to simplify the math). As we regulate this down to 58.8 psig (+4 atm), we are making 1617 * 4 = 6,468 scfm, or 1,293 cu in at +4 atm (58.8 psig). Multiplying this out, I show a potentially usable energy of over 76,000 lb-in. A tote weighs 7.8 lb, so that's about 9,750 tote-inches, or 5 totes times 1950 inches. If each lift is 25", this is still a total of 78 lifts. That's 78 lifts of 5 totes 25 inches. There were only 30 totes behind the walls, so even without doing any optimization beyond not pressurizing the down stroke, there is more than twice the required energy in one 7 gal tank to stack all of the totes behind the wall. (Though I haven't done any flow calculations to determine if it can be done in 2:15!)

With a 10 pound air tank, this obviously won't get down to 15 pounds, but I expect that it can be done for well under the available 35 pounds, including tank, cylinders, frame, tether, and electronics.