Saturday, November 2, 2013

Lighting Rig v2.0

Since 2001, my gaming group Rogue Cthulhu has used special effect lighting in our game room at Origins. To hold all the lighting equipment overhead, I constructed a custom lighting rig, which consisted of four telescoping upright posts and two 20 foot long sections of an aluminum ladder.
 It has undergone a few modifications to improve its stability over the years, but it has essentially remained unchanged since it was first built. Like any system, it has its drawbacks. The fact that all four posts have to be raised and lowered simultaneously was a big one. Also, those ladders are difficult to store and transport, and they don't provide any adjustability. I've been telling myself for years that I was going to build something better, but cost, portability, weight, and simplicity kept bringing me back to the same design. This year I finally made some progress on improving the RC light rig- starting with getting rid of those damned ladders.

While it's hard to beat aluminum for its strength to weight ratio, the ladders were really overkill in the strength department. They are capable of holding several hundred pounds of load, while we only really needed to use about fifty pounds of cords and lights. I looked at several (many, many) material and design options to replace the ladders. I needed something lightweight, easily portable (probably modular with sections no longer than 8-10ft), durable, cheap to build- requiring no equipment or skills to which I did not have access, and able to span 20+ feet with no center support. That last one was the killer. Lots of things can span 10ft. with no problem, even 15ft. if pressed, but 20 or more feet with no center support and you start to have troubles. In order to have the strength to span that distance and hold any kind of load safely, your truss starts to become huge and heavy, and its own weight becomes an issue. Although I had trouble with using wood as a material for the upright posts (warping, splintering, etc.), it gave me the best strength to weight ratio that I could afford. After looking into several truss designs, I decided to make telescoping sections of square tubing out of 3/8in. plywood.
 The plan was to make several sections of rectangular tubing. Some would be slightly larger and would slide over the others. Each truss would be made from three sections; one outer tube in the middle with one slightly smaller tube coming out each end. The outer tube would have to be completely hollow inside, but the inner tubes could have bulkheads to give them strength and stability without adding much weight. I ripped a sheet of 3/8in. plywood into strips. The strips, when put together, would make a box (tube) roughly 6in by 7in by 8 feet. I also cut 5/8in. MDF into rectangular bulkheads to fit inside the smaller tubes. Though I didn't have an immediate need to, I drilled out the centers of the bulkheads because I would never have the opportunity to again. Also, it cut down a little on weight.
Five bulkheads were equally spaced along the 8ft. length of the tube. They were glued and stapled in place. A prodigious amount of clamping was done to ensure a tight glue bond. The edges of the plywood, where they came together, were also glued and stapled. For maximum strength, I used a LOT of staples. About one every two inches. Hey, staples are cheap!
 Before the last side was glued and stapled into place, I gave the interior a good coating of stain and polyurethane mix. Then, after the last side was in place and the glue dry, I sanded the exterior smooth with a belt sander, making sure to round off the corners to avoid splintering and to give a little clearance at the corners when the sections were fitted together. Since the sections would need to fit together with minimal clearance, and yet slide smoothly, I needed the exterior of the inner tube (and the interior of the outer tube) to be very smooth. After sanding, I gave the exterior two coats of stain and poly mix, sanding between coats. Here are two of the inner tubes finished. One is still waiting to be stained.
Putting together the outer tube was a little trickier. The interior of the outer tube had to be nice and smooth, so the strips had to be sanded before assembly. Since it didn't have interior bulkheads to keep the sides square while gluing and stapling, I used one of the inner tubes as a temporary bulkhead. I put some glue along the edges of the boards, then clamped the walls of the outer tube to the sides of the inner tube, got everything square and even and then stapled the crap out of it. I had to be very careful to send the staples in straight. I couldn't have any staples sticking through on the interior side, and I couldn't have any splintering.
After the staples were in, I removed the inner tube so I could clean up any glue that smooshed out the seam. I didn't want it to end up gluing the two tubed to each other!
This process was repeated for each side, letting them dry before moving on to the next side.
When three of the four sides were together, I gave the interior a nice heavy coat of stain and poly mix. Then the fourth side was glued and stapled into place (without the inner tube).
 I was careful to make the seams as strong as I could, but without interior bulkheads, the outer tube would be too weak to be used the way I wanted. The stress of the inner tubes prying the sides apart at the ends as the load bore down on the center of the truss would be far more than the glue and staples along a 3/8in. edge could safely handle. And since this thing would be holding lighting over the heads of dozens of people, it needed to be reinforced. I accomplished this be using steel strips to bind around the outside of the tube, like the rings of a wooden barrel.
 The steel flat-stock was bent at right angles in a vise, then taken over to the work piece and measured for fit before the next angle was bent. This was repeated until the steel wrapped all the way around the tube, very snugly. The steel was cut so the ends would just meet and then they were welded together while being clamped tightly to the tube.
I wouldn't have been able to do this last part a few years ago. I just learned how to use a MIG welder at my current day job. I'm no professional welder, but I get by.
 I put four steel bindings on the outer tube. One at each end, and one more about two feet from each end. When the inner tubes stick into the ends of the outer tube, they will only go in about two feet. That will put most of the stress from the cantilever action on the seams at this two foot section at the end. With two steel bindings at each end, it should have no trouble holding together under that stress. I did a stress test with a scrap outer tube (I glued the wrong sides together) without any steel bindings. It held up over a hundred pounds of dead weight, but started to crack when I stood on it (300lbs.).
 After the bindings were in place, I gave the exterior two coats of stain and poly mix. I wanted to have every part of the truss stained and polyed not only for looks, but for smoothness and to help prevent warping.
Here is the full length truss being held aloft by two DJ lighting rig stands that I bought off of eBay. The center section is not stained or bound with steel (it was the scrap one that I glued wrong). With two feet of overlap at each section joint, the overall length is 20ft. I can push it to 22ft if I only overlap 12 inches, but that's as far as I think I should go. As you can see in the photo, there is no deflection at full extension without a load.
I made two of these trusses, to replace the two ladder sections. For their implementation at Origins 2013, I put one of them on the old telescoping uprights and one on a pair of new DJ lighting stands I bought on eBay, and then modified (more on them in another post). You can see a slight deflection in the picture below, but that is not due to the weight. That is due to the 1/8in. gap between the large and small tubes. It was hard to cut and fit the pieces together under tight tolerance, and I was afraid to make them fit together any tighter, for fear that future swelling and warping might make them not fit together or slide properly.
Once the pieces were slid together on site, laying on the floor, I drilled through both outer and inner tubes simultaneously and pinned them together with a piece of all-thread and some nuts and washers at each end. I was going to pre-drill a bunch of holes along the length so it would be adjustable but decided it would be easier to just re-drill holes at whatever position I wanted on site. When it gets full of holes and hard to line up properly (in 10-12 years, I can always re-make them.
The lights were held up with mechanic's wire wrapped around the girth of the truss. The electrical cords were taped up with vinyl electrical tape. I did drill out more holes in the old uprights to make them more adjustable for height. Now that Club Carcosa is over, we only use about 25 pounds of lights and cords on each truss. These trusses can hold more than four times that amount, so we have lots of room to expand our effects repertoire, and a stable platform on which to mount it.
The truss sits on top of the uprights without being clamped down. The wide base of the truss allows it to sit flat on the top of the post with no worry of twisting. The truss has a hole drilled in the bottom near the end which rides on a pin made from a 1/2in. bolt, which sticks up from the top of the upright, about 3in. In order for the truss to fall or slide in any direction (other than straight up), it would have to jump straight up more than 3 inches. I figure, if it does that, we've got bigger problems! And I can always put in a strap or something to keep it from moving in that direction.
 The sits-on-pin design means that the truss doesn't need to be clamped down. Since it can float on the pin to some degree, the two uprights can be raised and lowered independently (or at least they don't have to track perfectly with each other like they did before). Also, one of the modifications I made to the uprights was to put bigger bases on them, so they would be more stable without having to have all four joined together. This allows us to move the two trusses farther apart or put them at odd angles, and allows us to raise and lower them independent of each other. That's a big improvement over the previous design.

 During Origins, we extended the new trusses to 22ft, and they seemed quite stable and safe, and were much easier to work with than the ladders. Sadly, the new DJ stands didn't work as well as I had hoped and the old uprights I had build out of 2x4s ten years ago actually worked better than the new manufactured steel ones. The trusses are a bit lighter than the ladders, but not as light as I wanted. They do, however, transport much easier. Each section, truss and upright, is no more than 8ft. long, so they all neatly fit inside the bed of a full sized pick-up truck.And two of the truss sections can be nested inside one another to conserve space.

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