Oleo drop project

Just posted on the ERS Facebook page the following. Link at the bottom of this post should take you to the video.

“Sometimes the finished results are worth all the challenges, and who doesn’t love a good rigging challenge.

ERS designed and installed a new Oleo drop for the Barre Opera House that replaced the original drop.

Some details:
- Drop painted by Cobalt Studios (cobaltstudios.net)
- Tube is a pair of 20’ long by 8” diameter schedule 40 aluminum pipe spliced together with steel mending plates (engineered by Clark Reder Engineering Inc.) total weight approx 400lbs.
- Rigged as a double purchase manual counter weight system with a single wire guided arbor. Since the tube moves as it spins, it’s not a 1:1 ratio of arbor travel to tube travel. Since the tube is 8” in diameter we have a roughly 2:1 ratio (25.13” circumference). To have enough arbor travel distance we had to go with a double purchase system for our roughly 20’ of tube travel. Arbor, rope lock, and blocks supplied by J.R. Clancy.
- A pair of 1/4” GAC wire rope lift lines are wrapped in opposition to the drape. So as the drape lowers and unwraps, the wire rope wraps onto the tube. And vice versa when moving up. Much of the weight is actually supported by the drape itself.

On to the next one!”

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Way cool! And close to my neck of the woods, too. The scenic artists did a really nice job, from the looks of it. Was this a reproduction of the original drape, or a new one executed in the style of the originals?

Neglecting the thickness of the drape as it is rolled up, wouldn't any oleo drop (as usually rigged, like you described) have a 2:1 ratio of rope travel to pipe travel, regardless of the pipe diameter? It seems to me the pipe is basically acting like a single sheave pulley, and so the pipe diameter matters no more than the sheave diameter of a pulley in determining its mechanical advantage.

The very first venue I performed in, as part of elementary school music and drama stuff, was Robinson Hall, the town hall for Reading, Vermont. That venue has a number of original (and now restored) oleo drops and accompanying scenery panels. As I recall, they simply have ropes tied to cleats, with no counterweighting at all--but my memory on those details is pretty hazy. It was also sometime around the '90s that they updated their tiny stage lighting switchboard and replaced the bare knife switches and exposed autotransformers with safer but less romantic modern light switches and dimmers.

You mention using an aluminum pipe with steel mending plates. What measures did you take to reduce or eliminate galvanic corrosion?

Along similar thoughts, what's the minimum bending radius for 1/4" GAC? Is there concern about deforming the cable after multiple operations, or if it's left piled up on the pipe for extended periods?

theatricalmatt said:

You mention using an aluminum pipe with steel mending plates. What measures did you take to reduce or eliminate galvanic corrosion?

Along similar thoughts, what's the minimum bending radius for 1/4" GAC? Is there concern about deforming the cable after multiple operations, or if it's left piled up on the pipe for extended periods?

Click to expand...

The GAC is "piled up on the pipe" when the drop is in; the drop is "piled up on the pipe" when the drop is flown out.
Toodleoo!
Ron Hebbard

So good! Level and smooooooth.

theatricalmatt said:

what's the minimum bending radius for 1/4" GAC? Is there concern about deforming the cable after multiple operations, or if it's left piled up on the pipe for extended periods?

Click to expand...

So the D/d ratio for wire rope is 30:1. So for 1/4” wire rope you would want a minimum sheave diameter of 7.5”. Hence the 8” tube. The wire rope very nicely spools onto the tube even without grooves.

DrewE said:

wouldn't any oleo drop (as usually rigged, like you described) have a 2:1 ratio of rope travel to pipe travel, regardless of the pipe diameter?

Click to expand...

That's right. When flying in, you must spool 20' of line onto the tube (counter-spooling the 20' drop) plus add 20' of line to get from the "loft block" to the tube now on the deck.


Very nice execution on this oleo!

kicknargel said:

That's right. When flying in, you must spool 20' of line onto the tube (counter-spooling the 20' drop) plus add 20' of line to get from the "loft block" to the tube now on the deck.
View attachment 22221

Very nice execution on this oleo!

Click to expand...

Nice illustration to explain this operation.

Sure beats the static load weighted climbing rope we used to use! Needed pipe extensions just to have enough length to spool the rope.

jonliles said:

Sure beats the static load weighted climbing rope we used to use! Needed pipe extensions just to have enough length to spool the rope.

Click to expand...

Or a larger diameter pipe.
Toodleoo!
Ron Hebbard