Need a small turntable quick...HELP PLEASE!

[LD4Life]

I work for a university theater that is currently preparing for a production of Sondheim/Lapine's Sunday in the Park with George. For those of you familiar with the show, I am currently working on the design and construction of the Chromalume in the second act. The design, which was collaborative, requires the use of a 4' turntable to spin the top half of the device. The platform must support about 40lbs and, as it is on stage and elevated off the floor about 5', it must be motorized instead of cable driven. The final problem is that the DMX and power cables for three LED washes and a laser unit must pass through into the lower portion of the device. I have tried my best, but I am at a loss as to how to make this work. Any help that anyone can give would be greatly appreciated. I need to get this built as soon as possible, so I'm in a bit of a jam right now.
Thanks for everyone's help,
Rob Pelance
Student Technical Director
Master Electrician
Indiana Wesleyan University

[icewolf08]

First off, welcome to the booth LD4Life. Stop by the new member forum and introduce yourself. We love new people!

As for your problem, does the turntable need to revolve continuously? Doe it need to be able to stop in specific places and hit spikes routinely? Depending on the answers to those questions, you may need a motion control system.

Getting data and power up can be accomplished in two ways, both similar. You will need a revolve center that has commutators in it. Chances are you need two circuits for power, so 4 commutators for power (2 hots, 1 neutral, 1 ground... assuming your circuits are on the same phase). Then you need three commutators for DMX (common, Data+, and Data-). So that is a total of 7 commutators, that could make your revolve center pretty tall. The other option is wireless DMX, so all you need is power to come through the revolve.

As for driving the revolve, it is so small that you probably could get away with a fairly low HP motor, but you will probably need a gear reducer. You can probably connect the revolve right to the output of the reducer and do a direct center drive. You could probably also do a friction drive on the US side of the piece so it isn't seen.

I am sure that more people will be along with more advice.

[LD4Life]

Ok, it only needs to revolve for about 45 seconds to a minute and does not have to hit any specific spikes. It needs to start spinning when the device gets "plugged in" (which it actually is already but a character leaves stage to "plug it in"), but it doesn't matter how long it takes it to stop spinning or where it stops.
The DMX and power stuff presents a bit more of a problem. First of all, we are on a rather tight budget as it with all of the other complicated technical aspects that the show presents, so wireless DMX is not an option. Secondly, I have about a week to get this device designed and built, and I have no clue what you are talking about with commutators or how I would get ahold of them. I'm normally an LD and have been recently hired to my current position, so I haven't had a lot of experience with set design and construction.
I'm all for whatever drive system you would suggest. However, I have done even less with this kind of thing than I have with set design, so I have zero idea what the different types of drive systems entale. I'm sorry if I'm asking you to explain basic technical stuff to me, but I'm really new to this and want to learn. Any help you can give is appreciated more than you know.
Thanks again

[Charc]

What specifically needs to rotate? All 5', or just whatever is on top?

[icewolf08]

Not a problem on the asking lots of questions, that is what we are here for!

A commutator, or really in this case a slip ring, is w device that allows the transfer of electricity to a rotating drum. Here the most important info from wikipedia:

Originally Posted by wikipedia

A slip ring consists of a conductive circle or band mounted on a shaft and insulated from it. Electrical connections from the rotating part of the system, such as the rotor of a generator, are made to the ring. Fixed contacts or brushes run in contact with the ring, transferring electrical power or signals to the exterior, static part of the system.

You can read the rest here.

In simpler terms, the pivot of the revolve has a series of metal bands that rotate with the revolve. Each band is insulated from the others. The bands are wired to outlets or connectors, all of which moves with the revolve, thus no twisting cables. The pivot then sits in a sleeve that has metal brushes, one that contacts each band. The brushes allow a circuit to be made while allowing the revolve to spin freely.

While this would be the ideal way to build your revolve, it would be a big DIY project. I would imagine you can buy these places, though I am not sure where. I have one that if it came down to it, you probably could rent from us. PM or email me if you want to discuss that further.

The other option is that if you run the revolve slow enough over that 45-60 seconds that it is on, you may be able to get away with just letting the cables get twisted. You need to leave them lots of slack, and you need to remember to untwist after each show. If you choose to go this route you really need to pay attention so that you don't destroy your cables. You may find that to get enough revolves in you need to preset by twisting the cables in the opposite direction before each show.

As for the drive system, do you have andy motors and such in stock at your theatre? This could easily become expensive if you need to buy a motor. You will find that most motors suitable for this application will have very high RPMs. You need a gear reducer to get the rpms down to something usable. You get into lots of mechanical advantage and gear ratio math here. Ultimately you need to have the revolve moving slow enough to not throw everything off it, and you need to go fast enough for your effect.

The two drive systems that I mentioned before work like this. The direct drive, is exactly what it sounds like, you build the revolve so that it's center is the shaft of the motor or gear reducer. This is the simplest way to design the system, fewest parts. This system also requires the output RPM to be exactly what you want it be.

The friction drive uses a wheel/tire connected to the motor or gear reducer. The tire is placed in contact with the bottom or edge of the revolve and then when the tire spins the revolve spins. This can allow you more speed control as varying the size of the tire will change how fast the revolve moves.

I am not sure how helpful all that is, keep the questions coming and we will do what we can to help.

[LD4Life]

Ok, here's the 411. In answer to Charlie's question, this is the design for the device. It is shaped like a jewel, kinda like a diamond that you would see set in an engagement ring. It is 4' wide and about 6' tall. The bottom 4' of that 6' height are solid and attached to the carraige used to roll it onstage. The top two feet are constructed as follows. The diamond is six sided, with three of the sides made of plexiglass and three of metalic coated luan, all attached to a wooded frame. Within this shell are three Chauvet COLORado LED washes, which will be mounted on the turntable disk. The top face of the diamond will be inset enough to hold a laser projection unit. All of this amounts to about 40lbs and rotates as one unit.
In response to icewolf (i'm sorry, i've navigated away from anywhere that has your name or else i would refer to you by name), I am seriously considering simply letting the cables turn, possibly around a central post to keep it from catching on anything else. I have a pivot pipe with a center diameter of a bit over 3 3/4", so i will have no problem passing the cables through there. I'm only looking for 12-20 revolutions, so I can gauge the length of cable slack that I will need and construct it accordingly.
The drive system is my biggest concern. We have no stock in the way of motors, so we would have to buy whatever is needed for this project. I described above what needs to be rotated in detail, so if you have any suggestions as to what equipment to use and how to configure it, I'm all ears. I do have some rough renderings of the general shape of the device if you would like to get a better picture of what we are dealing with. They are in pdf, so if you want me to I can send them to you. Otherwise, any suggestions are marvelous, you have been an amazing help so far.
Thanks

[LD4Life]

The motor for the unit is the only problem I am still dealing with, the rest of it is now designed and being built. I would appreciate any help I can get on motorizing this thing. Please refer to the descriptions in previous posts for detailed ideas of what it looks like.

[Van]

Okey Dokey I see what your doing now. Here's a couple of hints.
Google "Display turntables"
There are a ton of companies that make them and they'll handle anything from a diamond ring to a HumVee. There is a company in Princeton,In. called Hansen Corp. they manufacture Slip rings < the commuters dicussed earlier> and they have a listing under "turntables here http://www.thomasnet.com/products/di...9661805-1.html
Though upon perusing their website I didn't see any listed. Perhaps a call first thing Monday might be wise. If they are local, perhaps you can get them to help/donate the necessary parts,
Couple of things to keep in mind about working with turntables. Almost all display turntable of the sort you are looking for are hmmmm what's the word... Clutched, I guess would be the best word for it. If you've ever used a mirror ball you know how the mount for the ball will actually spin freelly if twisted. This is to keep the poetential energy of the rotational momentum from destroying the gearing system when the motor shuts off.
< I'd be happy to explain that some more if necessary, at a later time.>
All display turntable are similarily constructed, so when picking out a wieght rating be sure to get one that will allow you to turn your weight without then spinning for an hour after you shut it off. If you've got one hundred pounds of gear and framing and you need it to turn and start turning on cue you need to make sure your turntable is rated for at least 180 - 260 pounds, this will allow the slip joint to overcome the initial Rotational torsion and allow it to stop a bit sooner after the motor is turned off as well. It is important that the clutch action of theses turntables not be defeated eg. " Hey let's just weld this shaft solid...."
In so doing you would remove a key safety feature. the slip joint protect you if ;
A. Someone were accidently trapped under the turntable.
B. If a cable runing through the center of the turntable were to snag.

Remember you are going to have to balance your load very well, so keep that in mind when computing the load capacity of the turntable, you may need to add even more weight than just your gear, you may have to counter-balance your gear with sand bags, or stage weights to keep everything on an even keel.

I hope that helps.
If you want some Turntable Horrors stories I'll be happy to relate a few, in a week or so.



< Sorry for typos, grammar, punctuation, etc. etc I'm opening tow shows within two weeks and haven't started the second on yet........... can you say screwed?>

[LD4Life]

Yeah, would be great if we could just purchase a unit, but we're on a rather limited budget due to other high-dollar technical things for the show. I have the design down and have started the actual construction of the turntable, right now I'm trying to figure out the best way to configure a friction drive to power it from within.

[cutlunch]

A dumb question but what about person power. You said the base is 4 foot wide. Is the base see through or dark? Does this prop come on / off during the scene or is it pre-set / struck in darkness. A small stage crew member could fit in the bottom and have big vale type handle to turn it by. You could put little wings on the base that come out sligthly to hide their legs. Just a thought. If is only turning for 45 seconds it shouldn't be too hard.