Will pneumatics work for this?

Pneumatics would do fine, and I was thinking of a water brake or sorts to keep the rate controlled. Vacuum might be easier to work with. This way the only time you need the actual vacuum would be to lower the platform, then let a counterweight raise it. It won't pass OSHA, but its simple. By controlling the rate that the vacuum re enters the cylinder (controlled flow check restructure sort of thing) you can let the cylinder do the braking. Not at all dissimilar is a vacuum elevator. Google for "vacuum elevator"

Maybe using cables and a governor on the windless to slow down the upward movement? Ken.

Very heavy duty gas shocks? Kinda like on a hatchback door, except much heavier. This dampens out the load by a significant amount.

I don't think pneumatics is a good choice because it will do nothing until the pressure gets high enough then it will snap up. Hydraulics is more controllable and can move at a set rate less dependant on the load.

Correct about favoring hydraulics over pneumatics -- but a properly-designed and maintained hydraulic system moves at a rate completely INdependent of the load, so long as the load is within the design limits of the system. Leaks and poorly maintained pumps can mitigate that. But for most purposes, you may think of an hydraulic system as a true positive-displacement mechanism.

LLoyd

If you use a double acting pneumatic cylinder and a counterweight system, you only need air on one side of the cylinder. Fill the other side with oil and connect it to a reservoir of oil through a needle valve. This will allow very good control of the speed of the outstroke of the system. It will however do nothing for the return stroke. I suggest that you could put a one way valve in parallel with the needle valve so the return stroke is not restricted as all it will do is cavitate the oil in the system.

Tom