[SML] Air bladder system for pushing down casters....

[Jon Lagerquist]

Years ago we did a number of units that moved about on stage and we 
lifted them using several small inner tubes to raise the scenery. The 
casters where on a single plywood plate and the units had matching lift 
points. As the tubes where all in the same loop there was some 
unevenness in the lift, the lighter end would lift first and higher. Not 
lots of pressure required but more volume. For those we used a simple 
three port manual valve like 
<https://www.automationdirect.com/adc/shopping/catalog/valves/manual_air_valves/miniature_manual_valves/gvs-521f-td>. 
It worked but I never felt a need to repeat the experiment.

Exhaust noise is generally easy to control. The easiest way I have done 
it is simply putting 100' of tube on it. For moderate sized systems that 
lets the air decelerate before it is released into the room. For 
stationary systems running the exhaust tube into a wall works and scares 
the mice. Generally my muffler of choice is like the one that Loren did 
a Tech Expo (I think it was there) on. Take a clean 20oz Gatorade 
bottle, drill a 3/8" hole in the cap. Run your 1/4" tube through and put 
a T on the bottom so it does not get pulled out. Wrap a 6" square of 
sound absorbing foam around the tube and work it into the bottle. Screw 
on the cap and you are done.

Attached is a drawing for the latest version of the pneumatic feet I 
used for many years and one for the more complex plumbing that gives you 
two control points and the ability to adapt to different loading. These 
show a double acting cylinder but if I were to build a set from scratch 
with all new bits I would use spring retract cylinders to 1) fail up and 
2) reduce the already small air use. The key thing is to adjust the 
pressure to the cylinders to just under what will lift the unit. That 
way you get the breaking force and do not move the unit. The box serves 
to absorb the horizontal load so the cylinder does not get tweaked.

Jon

On 8/5/2024 2:01 PM, Jon Ares via Stagecraft wrote:
> So this is still a dream of mine, perhaps.... according to my files, I
> queried the SML about air caster/diaphragm technologies, for wagon
> brakes. (An air bladder, pushing down on casters, thus lifting the
> platform, and allowing it to roll.). Michael Powers gave me great info
> on systems he'd built, but it all seems like a ton of work, with lots
> of trial-and-error.  (I'm always short on time, not a lot of time for
> extensive lab testing.) :)
> 
> Has anyone tried building a system using something like these,
> commonly available today?
> https://www.amazon.com/IMPROVED-Commercial-Professional-Alignment-Inflatable/dp/B09F34QGB6/
> 
> My thought was replacing the tubing and valve with appropriate air
> fittings, but also not sure if there's a two-way fitting that allows
> inflation and deflation all at one junction.
> 
> Or other methods to quickly, quietly, secure rolling wagon units
> onstage? I despise "wagon brakes" - the hold-down clamps repurposed
> into "brakes." I do have a 4-brake pneumatic system that can work, but
> it's a bit noisy (the loud PSSST! when releasing them) - plus, I'd
> need many more than 4, which means getting more stuff, and if I need
> to get more stuff, I might as well look at other options...? Leading
> me back to the air bladder option, where air pushes down on a plated
> caster, thus lifting up the platform and allowing it to roll.
> 
> Open to suggestions.
> 
>   - Jon
> 

-- 
Jon Lagerquist
--
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