Wagon casters

[bobgaggle]

I just saw the most recent tour of My Fair Lady at the Kennedy Center in DC. I got to go on a backstage tour of the show and noticed the wagons they use to move scenes on and off. Naturally they used a tracked deck with a cable system to move the wagons, but I couldn't figure out what kind of wheels they were using. Of course we weren't supposed to touch anything, but as the group moved forward I couldn't resist. I lagged behind and gave the thing a shove. Needless to say it sailed like a ghost 7 or 8 feet across the stage before the cable jerked it to a stop (and I probably fouled it up in the motor too

But I have no idea how they got that thing to be so silent and so low to the ground (it was 2" max off the deck) Anyone know how to do this?

Air cushion?
Uber soft rubber wheels?
Mag Lev?
The Force?

[Van]

Hmmm Good question. Don't think it would have been air casters, as they require a constant supply of air when lifting, and you certainly don't leave big wagons lifted when tours are comming through. Were the wagons tracked with a rail on the stage? In that case I say it was probably dual or right angle roller ball casters. Or maybe, since it's a big show they have the money to buy really good ball bearing casters, unlike us schmucks in the Non-Profit world who get by on rollerskate wheels and 1/4" bolts.

[soundman]

Just come in during preshow and ask the tech that is rewraping the winch system what kind of casters are on it.

Was the clearance two inches or the total height? If it was total hight and the units were light weight they could have used shop built nylon rollers or just stuck UHMWPE on the bottom of the unit http://en.wikipedia.org/wiki/Ultra_h...t_polyethylene

[derekleffew]

It's been 25 years since I've spec'd casters, are Darnells still the Rolls Royce of the industry?

[bobgaggle]

Total height (not clearance) of the wagon was 2". I've been googling like mad and I can't find anything. The wagons just had two knives in the track (on in front and one in back) to which the cable was attached.

Doing a bit o' research on UHMWPE...is it really low friction?

[soundlight]

Originally Posted by derekleffew

It's been 25 years since I've spec'd casters, are Darnells still the Rolls Royce of the industry?

Yes, they are. Dunno if the name has changed since you spec'd though, the full name is now Darnell-Rose but I just call the casters Darnells.

Ooohh...2" total thickness...now I really want to know what the deal is here!

[soundman]

Originally Posted by bobgaggle

Doing a bit o' research on UHMWPE...is it really low friction?

Yup to most surfaces in low weight applications it will glide quite nicely.

[bobgaggle]

so what defines low weight? would it glide with a desk on the wagon? a few people? only a folding chair?

[soundman]

If you don't have a copy of Technical Design Solutions for Theatre buy volume one and look pages 210-214 because there is a very well written write up of several different plastics that can be used as guides.

Using the Formula F=UN where F is the amount of force to start movement, U is the coefficient of static friction and N is the weight of the object being tested

UHMWPE has a U value of .17

you can do the rest of the math to figure out how much weight you can apply and still only need to give it a good shove.

[themuzicman]

Originally Posted by soundman

If you don't have a copy of Technical Design Solutions for Theatre buy volume one and look pages 210-214 because there is a very well written write up of several different plastics that can be used as guides.

would that be the book you mentioned?

http://books.google.com/books?id=5zu...with-thumbnail