Trouble with Electrics

[StradivariusBone]

We have a single-purchase counterweight rigging system with two dedicated electrics. Both are on truss with baskets on top of the truss to catch the multi cable feeding the batten. When I took over here, my predecessor familiarized me with the linesets and explained that moving the 1st electric required three people pulling on the hand line to get it moving. It's almost impossible to move by yourself, I weigh 250 lb and have difficulty using my body weight to get it started, however it does not pull as though it is out of balance. We've run it in and out several times and not ever has it tried to run away. The weight in the arbor looks to match the weight on the truss, also the capacity of the arbor is rated to 3,000 lbs and we are at 1,800 lbs.

The second electric is easier to move, but still challenging with a single person. In doing research and asking around, I've found that some people claim that this isn't that unusual when you think about the inertia in 1,800 lbs of arbor. Others have said differently. I recently found out another theatre in our area that has the exact same design has no problem flying their electric in and out.

This is a Secoa system and it utilizes the compensating cable on the back of the arbor. From what I understand, as you raise the truss, it takes more of the weight of the copper cable in the baskets and as the arbor descends, this 3/4" steel rope rolls over a head block onto the arbor which takes the extra weight.

None of the other linesets are this challenging to move. On the compensating cable, there is a lot of dust buildup on the smaller cable that threads through the block by the tension blocks. The only other thing I can think of is maybe the guide rails are out of alignment in some way? There is a point where two guides meet, and a few arbors will make a slight bump as they slide over it.

Obviously, I'm planning on pursuing maintenance on the system at this point. Our county has a contract with a rigging company in the area. But I did want to seek experience from the board as well.

Thanks!

 

[kicknargel]

Are the arbors directly in line with the battens? I've worked in a house where they're not, and the turns the lift lines had to take in the grid made a noticeable difference in the friction in the system.

 

[StradivariusBone]

Are the arbors directly in line with the battens? I've worked in a house where they're not, and the turns the lift lines had to take in the grid made a noticeable difference in the friction in the system.

They are. This is an underhung system I should add too, no grid. Just blocks on I-beams on the overhead.

 

[Tofudesperado]

You might just have a lot of gunk and grime in the blocks. They can build up and make everything to heavy.

 

[BillConnerFASTC]

I've designed 5000 pound pieces on single purchase manual counterweight that I can move without much struggle. (The ones I'm thinking of were installed by SECOA it so happens.) Lately, I have designed the handline to be double purchased (when I can't motorize them) and that works slick.

If there is any back muling - or any muling at all - I find that often adds a lot to overcome. But 1800 pounds should not be that hard to move if basic straight lift. Most general purpose sets I do are 1500-2000 pound capacity and orchestra shell ceiling are often over 2000 pounds. Something is wrong. I'd recommend hiring SECOA to schedule a visit and diagnose.

(I don't like that method of feeder cable management on manual counterweight electrics - but should be able to work easier than you describe.)

 

[StradivariusBone]

It's hard to tell since we don't have a grid, but it doesn't appear to have many mule blocks out there. I'll be the first to admit, I lack the experience of many on this board when it comes to these things, but I don't see any of the telltale warnings prescribed in Mr. Glerum's book as well as resources from SECOA. However, after I watched the same truss on the same system with the same weight (at a different, but identical venue) be pulled in by a kid that was 110lbs soaking wet, that's what really made me go ->

The feeder is encased in PVC pipe at about 6-8' lengths and kinda stacks on itself as it flies out and unfolds as it flies in. I can see where that could get fouled occasionally. What's your experience with the compensating cable? I've heard some carry a dim view of it.

 

[SteveB]

I'm also wondering if a cable has slipped out of a pulley. That would cause a lot of drag.


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[FatherMurphy]

We had a couple of linesets at a local venue that were nearly impossible to move *empty*. Upon inspection, we discovered that the head block axle had sheared on one side, dropping the sheave down at an angle, rubbing the frame at top on one side, and at bottom of the other. System was an original 1920's installation, and has since been replaced, thank god... it was the second scariest system in town.

A bad bearing in one of the blocks could introduce a lot of friction, much like a cable out of its groove.

 

[BillConnerFASTC]

No noticeable noise when moving? Its hard to diagnose without a grid or other built in access and getting a lift or scaffold in is not a simple affair (which is why I now refuse to put rigging in new build without access for regular inspection - a ladder or stairs and a grid or modified grid.)

Good lighting - aim some really bright units up - and good binoculars might give you a clue. Or your own helicopter drone with an HD video camera - who knows - you're in aerospace country.

 

[StradivariusBone]

No grinding or scraping sounds other than a soft whoosh of the arbor in the t-track. I should have mentioned this earlier, our lock rail is above the deck and our loading gallery is at the top, just under the head blocks. From this spot I can look out and see the lift lines and pretty much reach out and touch the head blocks. Can't actually get to anything else, but it's better than nothing. We do also have a Genie AWP, but as you've said- actually getting that to where it's needed is a chore too. I've attached a photo of the head block on our 1st electric for reference. I will inspect them again, first thing Monday, the head block didn't appear to have any issues like a sheared axle, but I didn't specifically look to the loft blocks for the same issues. I'll also check out the tension blocks too.

Do you think an email to SECOA would be prudent at this point? I'm learning that the county is a bit slow to react when our rigging systems are in disrepair (3 months to repair a cracked pulley at another venue). Another TD, with more rigging experience, is coming to check it out next week too. I'm just curious if they recommend cleaning anything specific first? I've found they do not recommend any re-lubrication on any of the blocks.

I do like the helicopter drone idea! We'll put in a request with Elon Musk and SpaceX.

 

[zmb]

Just curious, have you found any stray metal shavings or filings that don't have an explanation except they came from above?

One of the places I work has this with the ladders, extremely hard to take in and out even though the weight is balanced. Have had the installer in and they said there isn't anything they could do.

 

[BillConnerFASTC]

I don't see anything that looks amiss. The cable weight compensation is bound to add some friction. The fact there is another similar lineset that works better makes me think the most likely explanation is some misalignment in the loft blocks. I'd put a jumped grooves or crossed lines in that category.

It can't hurt to contact SECOA. It will cost a lot to just say be here next week or something like that but if you can work with them to schedule a visit when they are near on another project, it shouldn't be too expensive. I assume this is more than a year or two old - because under two years, they should come back at no cost.

 

[StradivariusBone]

No to the metal shaving question - even on the deck and it's from 1995 so we're a bit out of the warranty timeline.

 

[StradivariusBone]

So after doing some homework on this today, I have a little bit more to report. This image is the head block for the electric that we are having the most trouble with. The pulley seems to favor the one side of the block, but when it's moved I don't hear any grinding or any sound really from the block. There's no evidence of abrasion anywhere (scratches, metal shavings, etc) so I don't feel that this is scraping here.

None of the wire ropes are out of the loft block pulleys from where we can see either. There are no mule blocks in this setup.

The only thing I did notice (albeit not on the 1st elec, but the 2nd when we flew it in to change some cyc gels) is that the wire rope that comes off the bottom of the arbor is very slack, especially when the electric is flown out. It seems like the bottom block for the compensating cable might be binding so when the arbor moves down and compresses that cable, there's enough slack in the whole assembly to allow this cable to go way loose. This of course is just a theory. I have arranged for a neighboring TD to come visit and take a look, but at this point that's the only thing that looks amiss to me. The bottom block for the compensating cable rig is non adjustable, so conceivably any adjustments to the tension of that cable assembly would have to be done at the arbor (top or bottom) or on the hardware plate where the smaller wire rope connects to the two larger weight cables. I'm thinking that would be tricky since the whole purpose of this cable assembly is to just be really heavy. I don't plan on attempting to make adjustments on my own, FYI.

To expand on this:

I borrowed Mr. Glerum's diagram to show how this works in case anyone else who's unfamiliar might be curious, I apologize in advance for said borrowing. At the top, two 3/4" steel ropes go over a pulley and runs basically in the same manner that purchase lines go, except behind t-tracks. About halfway down, the 3/4" is attached to a plate that has two sleeves that ride along two vertically mounted pieces of 1/4" steel rope to act as guides when the plate's moving up and down. At the bottom of the plate is a 1/2" steel rope that goes through another block on the bottom and then attaches to the bottom of the arbor. I'm seeing cable slack in the spot between the bottom of the arbor and the bottom pulley on the stage side of the assembly.

All-in-all, I think it's a really clever idea. The concept being that the 3/4" wire rope is really nothing more than a ballast that is loaded onto the arbor in an identical fashion that the feeder cable is loaded onto the lighting truss, mimicking the added weight.

I'll keep updating this thread as we learn more if for nothing more than the good of the order. It seems there's a dearth of information online about the compensating systems, but I might be looking in the wrong places.

 

[BillConnerFASTC]

I think that's the hard and expensive and add-friction way to do cable weight compensation, but so be it. I much prefer a roller chain - approx length half of arbor travel - tag one end to bottom of arbor and one to middle of T wall. Works slick and quiet and nearly frictionless.

But that doesn't solve your problem. Can you get high on loading bridge and look/photo across stage? Maybe use a laser pointer and see if the blocks are in a straight line?

Of course could be a block bearing has just seized - very hard to find without being at the block with tools.

 

[StradivariusBone]

I much prefer a roller chain - approx length half of arbor travel - tag one end to bottom of arbor and one to middle of T wall. Works slick and quiet and nearly frictionless.

The chain method does sound a bit more elegant than this. I have a feeling this looked really good on paper, but in actual function it's a bit more problematic and adds more points of failure.

I will get aloft again tomorrow morning, hopefully with a better camera than my phone and see what we can discover. Thanks for all the advice so far, Bill.

-ED

 

[StradivariusBone]

Reviving an old thread on the same subject rather than starting a new one altogether, I figured that'd be better forum etiquette.

To recap up the previous bits of the thread HS PAC with a SECOA installed CW single purchase system. 2 dedicated electrics with multi-cable that is collected in baskets and a compensating cable assembly that consists of 2 3/4" lengths of wire rope that roll on top of the arbor as the basket on the truss takes more multicable.

The 1st pulls with a lot of drag compared to the 2nd and they both are built the same. We stripped the pipe today, pulling about 350# of lights off it, found that it was happier balancing about 40-60# arbor-lighter and moves slightly faster. One thing that was noticed is that a rumbling, grinding sound can be heard coming from the headblock, along with what feels like intermittent binding and releasing in the purchase line. I'm about 95% certain it's the headblock, but have no way of really knowing if that's all since we don't have a grid. I don't think we noticed the grinding before since we couldn't move it fast at all. It's definitely coming from the headblock.

In the past, our school district has contract with Tom Kat Rigging up in Georgia, however I am uncertain if they still use him as a vendor, I'm currently going through the fact-finding process for that. I'm also uncertain if there's anyone closer that would be capable of performing this work. Any recommendations close to central Florida would be appreciated!

An inspection would also be in order, to verify that it is the headblock bearings that have failed. The biggest trouble in all of this seems to be the fact that we'll have to de-rig the electric truss which weighs about half a ton by itself. Building some supports to cradle this thing will be a chore and put us out of business for some time I'm anticipating.

 

[BillConnerFASTC]

Do you think the noises could be a problem of different size cables and ropes and not having the right pitch diameter for each on the head block, so one is actually sliding instead of rolling?

I think there are some good folks at Main Stage in Pensacola; some of the best at Interamerica Stage in Orlando, and I wouldn't hesitate to contact Ty at Bellatex up in TN. The fact is that many of the major riggers have crews far and wide, and can schedule a no obligation visit. Texas Scenic is doing a BIG project in Orlando and I suspect SECOA is still active in the FL market. I know you have some issues with the SECOA work but they are the only ones that could unconditionally guarantee any modifications - everyone else will have to include CYA language since they can't know the pieces there.

 

[StradivariusBone]

It's possible, the other thing I still have to check is the tension block. It might be tight or at a strange angle that could be biting. The purchase line has very little slack in it.

I really don't have issues with SECOA, they built it and should know it best. I think the counter balancing cable was one of those ideas that seems really good on paper, but in reality there are some issues that crop up. I will definitely take down the other companies you mentioned and see what is possible.

 

[StradivariusBone]

Here's an update for the good of the thread-

Was visited by our rigger vendor today on his way from one job to another and he took one look at the head block and confirmed the dead bearing theory. He even was able to spot some grease on the side of the block, coming down from the center.

We discussed the options for removing the truss, being that it's 1300~# it's not a simple task. The two plans on the table are to bridle it between two pipes (good idea, but the upstage lineset is the shell and beyond that is pretty far) or to build a frame to hold the truss while we detach it. We have a marine mechanics shop/lab on site and I posited that he might be able to help since they often have to place sailboats on stands and they weigh as much if not more than this truss. So that's an option, not sure if it's a great one. It'd save my rigger friend the trouble of building the stands in his shop in Georgia and hauling them down here. I will keep following up for the good of the thread.

I should also point out that Tom Kat is the company we still contract with and he is ETCP certified and also a heck of a nice guy.