More considerations on this question: if lifting the casters the whole
unit does a little clunk up and down when shifting states. With brakes you can set the pressure so the brakes push into the floor without lifting the
unit. We've done this with 3-4" diameter pads with soft rubber pushing into the floor. It's still not AS secure as lifting the casters entirely.
And ANOTHER consideration: typically a large
unit may have
caster about 4' OC or more. That can mean a lot more lifts on casters vs. brakes. Or you frame the
base unit to be stiffer and need fewer casters. If it's not moving with people on it that helps; then when it's playing the frame is on the
ground and well supported.
Lastly, I remember a DIY version in Technical Design Solutions for
Theatre. Must be in volume 3 because I don't see it in 1 or 2. Everyone must own these books. I'm buying v3 now (I do have the original subscription pages).
If we're going to swerve into DIY concepts, try this one:
I'll provide dimensions purely as an example, smaller or larger boxes and inner tubes may be substituted.
Build two plywood boxes. Each box has a bottom and four sides, no top.
Glue and screw the boxes, make their joints REALLY solid.
Size and construct the two boxes such that one box inverts and slips over the other.
Make one box deeper than the other by the depth of the casters on the lower box.
CLEAR AS MUD SO FAR; I'll try and clarify:
Think of it this way:
Box 1; Approximate dimensions for illustrative purposes only.
30" x 30" x 8" deep.
Imagine box 1 sitting on the floor, open side up, four good quality 3" or 4" swivelling casters on the bottom.
Imagine box 2 slightly larger than 30" x 30" x 8" deep + the height of the casters on box 1.
Invert box 2 over box 1 and set it down.
Box 2 is now inverted and resting firmly on the floor.
Box 1 is now out of sight inside of box 2.
When you load (
build you set on top of) box two, it doesn't want to slide or tilt because it's sitting inverted directly on your
stage.
Build multiple pairs of boxes to support larger sets.
HERE'S THE TRICK:
Inside of the two boxes place a suitably sized inner tube, remember inner tubes from the era before tubeless tires?
When you inflate the inner tube, it expands in all directions. It can't expand very far laterally because you've sized it to fit your boxes AND you've constructed, glued and screwed both your boxes to withstand the pressure of the inner tube.
Thus confined, the only direction the tube can expand is vertically; when it expands vertically, it lifts box 2
clear of your
stage floor placing all of the load on the four GREAT casters you've securely attached to the bottom of box 1.
Your set is now elevated on your DIY air-ride and free to be pushed about your
stage.
Releasing air from the inner tube deflates the tube and box 2 again returns to its inverted position resting directly on your
stage.
NOTES:
1; You need to construct, glue and screw both your boxes to withstand the pressure of your tube trying to expand in all directions.
2; You need to accommodate getting air into your inner tube while it's trapped within both your boxes, this will mean providing a gap and / or slot(s) to facilitate the passage of an air hose.
3; You need to be able to fill the inner tube, retain its air under pressure, and
release its air on
cue when desired.
No, I didn't dream this up by myself. In the late 1970's a touring production toured our large soft-seater.
The show involved two complete sets each approximately 40' wide x 20' US / DS.
Each set included its own floor, carpets, walls, doors, stairs, second levels,
escape stairs for performers, furniture, appliances and
practical lights.
There were multiple scene changes between the two sets.
The
road crew dealt with all aspects of the air, its couplings, valves and muffled exhausts.
Thirty or forty of my local IA brothers rolled one complete set into one
wing while the second set rolled on from the opposite
wing.
Being the Assistant LX, I had it easy only having to
page cables for
practical lights and keep them
clear of the feet of my grunting brethren.
We'd heard about the production before it arrived, including its requirements for local crews. We all giggled and snickered during the in.
We weren't snickering when we watched how well it all worked performance after performance nor were we snickering counting the money we made while watching the show and only doing any real work during scene changes.
That's my DIY air ride tale and I'm sticking to it.
Toodleoo!
Ron Hebbard