Stage Revolve (Motor and Power Question)

[rapscaLLion]

Sorry, not sure where this should go.

I am building a 16' (diameter) stage revolve. It will consist of floor mounted wheels upon which the platform will ride. There will be a pivot at the center to keep the platform centered, but is not load bearing. The set is built on top of this platform and may require some household lightbulbs and possibly a fog machine (with DMX cable). My problem is how to run power onto the revolve? I figure running cables under the platform to the center and then up through the pivot (then back through the platform to the devices that need power) is the best and simplest way, however I am concerned about the cables getting too twisted. The revolve may complete multiple rotations in one direction before reversing. Is there any way to solve this? Or should we put a limit on how many revolutions the turntable can make in one direction?

Also, a question about motors. We are going to use a permenant magnet DC motor to drive the turntable. Which method is cheaper/easier? Belt driven via the central pivot, belt driven via the circumfrence, or by direct contact with a spinning wheel underneath? The max rotation speed is slow but variable, and precision should be within 5 - 10 degrees max.

Any suggestions?

 

[Van]

I'll leave the electrical to someone else, though I know there are several techniques of producing electrical "races". As to the drive portion I would suggest you use a direct drive wheel on the underside of the outside diameter of the revolve. This will give you the most torque for horsepower, trying to turn a 16' revolve from the center pivot is next to impossible , 'specially when you get the added weight of scenery on it .
Now, just to CMA it's possible that if you don't have enough wieght on the outside edge of the revolve table, that the wheel might not get enough traction. This can be allieviated byt adding a "pinch wheel" on the topside above where your motor wheel makes contact withthe underside ofthedeck. If this is not possible then you may need to either add traction tape to the underside < Which I would suggest anyway> or move the wheel to drive from the top side of the platform.
Are you using a Stepper motor ? or some sort of passive feedback system to control the stop points ? Is you motor geared ? or straight driven? that will effect how accurate the start stop points are as well.
Good Luck Tell us how it goes. I'd love to see pics. I love a well engineered theatre project!

 

[rapscaLLion]

Hi,

This project is in the planning phase, and will most likely be built in increments. We will likely start with just a simple speed controller, but we are designing with the eventual aim of the computer controlled motor. But I will certainly post pictures, and likely a full DIY tutorial since everyone seems to like turntables.

I am hoping to engineer this one well enough to be able to rent it out to small tradeshows and school theatres and the like.

As for the direct drive idea, I agree that direct drive on the outside is best. Underneath is of course preferable since it is hidden. Traction tape is an excellent idea that I never thought of. Also, the point about weight... I am certain this one will have enough weight to work since there will be a heavy set attached on top, it's a good point regardless. I don't like the idea of a wheel on top because it is visible. I would rather not put the wheel onto the side for fear of warping the circle. Any other ideas for providing extra traction?


Also, what motor would you recommend to use. A stepper motor could work since it is already designed to do preset movements (ie- 1 degree). But would it be: A) Strong enough, B) Smooth enough?

 

[Foxinabox10]

For added traction, Home Depot or stores of the sort sell an additive for paint that you just mix in and paint it on. It's like little bits of sand, but it gives the motor more to grab on to. Wouldn't be a bad idea for the top either for when it rotates with actors on it too.

 

[rapscaLLion]

A great idea FoxinaBox. Extra traction on top for the performers is another thing I never thought of but makes sense.

 

[rapscaLLion]

Well no one seems to have any input, so I just thought I'd say I've invested in a couple stagecraft books that should arrive soon that will hopefully have some tips!

 

[cutlunch]

I would go with the friction drive because if the revolve jams the drive wheel will start slipping. On a belted system the motor will try to keep driving until the belt snaps.

For the cables I would bring them up through the center like you suggested. But I would wind the turntable back every so often to untangle them. On a professional system they would probably have a series of contacts and brushes. These can just keep revolving a round for ever so long as the contacts are cleaned.

How are you going to get your positional information. On some systems they use shaft encoders attached to the end of the motor shaft. But they can be quite hard to program and cost a bit.

On your system I was thinking that you could use reed switches. You would have a series of reed switches mounted very close to the turntable on the non -turning platfrom. Then you mount a magnet under the lip of the turntable so it passes within millimeters of the reed switch. When the switc closes you know where you are.

What voltage is the DC motor? Do you have a background in building speed controllers? I just ask because this one will have to be pretty heavy duty. You have probably already thought of this but make sure there is a safety stop switch that disconnects the motor from the power.

I just have been looking through an old second edition copy of "Scene design and Stage lighting" Parker , Smith. They have a small section on turntables. I would take it the later editions also had this section.

I am sorry I don't know your skill level but I would probably get some outside help with this project especially with the design of the turntable and it's load bearing. Also if you want to hire it out to other venues this adds another whole sets of problems. Eg how to make it portable to get into other venues, what if the floor in another venue is not level? etc

I look forward to your journaling of this project.

 

[j_blinker]

http://www.mercotac.com/ has rotating connectors that I've used in revolves. I just mounted it in the center pivot. It means you can only use a single connector so it has to have enough poles in a single until. The wheels up design will make it easy to run your power under the rotating deck. The hardest part of constructing a revolve is keeping its circle true and its pivot at exactly center. The wheels all have to be 90 degress to the pivot or they will drag. And if you plan on moving this thing around a metal frame is a big must.

As far as you DMX line you could rig in into the rotating connector but the resistance might wreck havoc on your data.

 

[cutlunch]

I forgot in my last post to disagree with Foxinbox about putting that traction paint on the top surface. This would cause to much friction for the dancers. If the deck is made out of plywood it should have enough grip just using an ordinary paint.

j_blinker those revolving contactors look good. If their spec's can be believed it could be worth giving them a try for the DMX. Milliohms of resistance shouldn't effect it, also they are rated for frequencies upto approx 100MHz. Do you make revolves for a living? Are there any more tips you can share with us. Also what is your normal means of drive, drive control, positioning reference? I understand you may not be able to tell us due to business confidentiality but anything you can will be useful. Thanks.

 

[Van]

Got to go with cutlunch. No traction over the general area of the platform top, only on the wheel traction area. Dancers would kill you.
Disagree with blinker, on the metal framing. I've had a revolved tour for over 5 years that is a completely wodden design and holds up quite well, not to mention it is quite light for a 16' diameter turntable.. Oh what the heck I'll post a nasty Acad drawing of it.

Ok it's a .zip file with .pdfs and a .dwg

 

[Foxinabox10]

On the traction on top, it depends on how much dancing is involved with the show and how often it is being rotated with people on it.

 

[saxman0317]

Ive seen set ups where you have essiantially a stationary plate under the plateform and brushes that contact that. Power into the stationary plate, goes through the moving brushes into a pocket on the table. ive had this set up a couple of times, but i always get someone else to rig it up...like a ME.

 

[rapscaLLion]

Ok wow where do I begin!

Cutlunch: I've pretty much decided on friction drive. I did think about the cables going up through the center and have decided to do that, with plans to upgrade to a mercotac connector later.

Positional information would be done via incremental encoder I think. I'm talking to a manufacturer of encoders right now running through options. It is likely that the first iteration will only use a manuel speed control, as I don't have time at the moment to write control software (since DMX should NOT be used to operate moving machinery!) I am also looking into using similar switches to the "reed switch" you mentioned. The encoder doesn't seem to be extremely pricy, but there is a problem in that they may not make ones large enough for the diameter I need.

I am getting outside help on the motor as well, no news on that front besides using a DC motor to turn a wheel
I intend for the operator to hold down a button while the revolve is in operation to make SURE that they are paying attention. There is also plans for an E-Stop at the operator's desk and off to the side of the revolve. I still have to clarify what laws apply to this here. I'm also looking at other sensors and such to ensure safety, including a "just in case" speedometer attached to a cutoff.

As for design, I'm getting outside advice on that as well. As for lending it out, I have no idea what the laws and insurance situation would be, so it's just a thought for now.


JBlinker: Thanks for the link, that looks perfect, I'll check it out. It will carry household AC no problem? I think I will want 2 AC, 1 DMX, 1 XLR and a spare.
What do you think?

Keeping the circle true is a hard part indeed. I have not decided between wood and metal, and will probably choose a combination of both. I don't think a metal frame is essential for transportation, as metal has its own set of problems, but I am considering it.

DMX isn't really a big worry for me, I could always spend a little more and go wireless for that bit.



Cutlunch again: I wasn't clear about my intentions, for the stairs and such that will be on the revolve temporarily I will use that, but the deck itself will be smooth and probably matte black on plywood.



Van: Thanks so much for the drawings. I was amazed to find that my plans are very very similar. I am having trouble with some though: Are there no supports that radiate from the center to the outside edge? Is it actually just the races that support the entire deck? Or is the section plan excluding something? How much weight can this revolve take?

So each of the wedge sections fits together in a similar fashion to what I already had in mind, but how do you attach them?


Saxman: Although I have access to a licensed electrician, I don't want to mess with creating something like that myself. Thanks though!




Alright guys, thanks for the enthusiasm and support, but keep in mind this project is at the research stage. I still don't have a green light, so I need to make this project as simple and cost effective as possible!

Thanks!

 

[Van]

I'll do a couple more detail drawings for you. I should have them for my archives anyway. I post a further explanation of the design as well. I'm in the middle of Tech week for a really big production for us right now so I limited time for postings, as well as being in the middle of getting my butt kicked by the worst cold I've had in a long time.

 

[rapscaLLion]

Thanks a lot Van, the timeframe on this is quiet long anyhow (we're talking finish by June if the project gets the go-ahead)

 

[Chris15]

I intend for the operator to hold down a button while the revolve is in operation to make SURE that they are paying attention. There is also plans for an E-Stop at the operator's desk and off to the side of the revolve. I still have to clarify what laws apply to this here. I'm also looking at other sensors and such to ensure safety, including a "just in case" speedometer attached to a cutoff.

I tend to think that an E stop on the operators' controls and one or two on the revolve itself would be sufficient. Just make sure you wire them properly (ie. as a normally closed switch in the main motor feed or with a relay or contactor performing the same. Normally Closed is the only way to do stop switches properly and safely - because if it fails, the power gets cut.) (An side note, the reason for an E stop even with a dead man's type arrangement for driving it, is that IF said switch mechanically failed and hence became latched on, then you use the E stop to hard disconnect the power.) I would also advocate using mushroom head buttons for E stops and make sure that they mechanically latch (you know, the ones that push on and twist to release, assuming these are in use over the pond.)
And a late thought, I recall seeing a circuit in something, I think it was for a garage door opener but that is irrelevant, but the important part is that it had a means by which it was monitoring the current across the motor coil so that if it changed (due to the motor being stuck) it would assume that it had hot something and in this case would reverse. Something similar may be of benefit in case the revolve gets stuck.

JBlinker: Thanks for the link, that looks perfect, I'll check it out. It will carry household AC no problem? I think I will want 2 AC, 1 DMX, 1 XLR and a spare.
What do you think?

...
​

DMX isn't really a big worry for me, I could always spend a little more and go wireless for that bit.

Based on the aforementioned link, carrying the current is not a problem, but the most contacts is 8, which would not take the signal as well as the power you were desiring. I would advocate that wireless DMX might be the best option, or if it is less critical, perhaps the use of DMX over Ethernet and a wireless LAN. If the XLR in question was for audio, then a radio mic might be the answer.

 

[highschooltech]

This seems oldly familar. My school did this a year ago. I wasn't on the build team but i helped with the eletrical parts. We contstructed a sacco breakout that used edison, but for you purpose it could be stage pin or just wire to a string of lights. In order to move the wall the cable was disconected then reconected when the move was complete.

 

[j_blinker]

I'm in my last of Technical Production at Sheridan College Ontario and Just finished a production where I was in charge of a 20' revolve and 4 periaktoi. They all needed a 15amp circuits that wouldn't be hindered by their rotation. The 2 pole connectors worked without flaw.

We went with a fairly simple drive and control system. A Mitsubishi Freqtrol modulated the supply AC frequency to speed up and slow down the AC motor without losing any precious torque. With a DC motor some kind of PWM would achieve the same result. Voltage dimming will slowy kill your amperage and torque and won't have the programmability of a computerized frequency mod unit, but is way cheaper. With the Freqtrol several ramp up/down, and running speeds could be programed in and easily controlled with a pickle and a couple limit switches. Limit switches are no good if you need to set the revolve to several different stop points out of order, but to jog through a series in order they're perfect.

The motor ran a small tire that could be tensioned by 2 threaded rods for more friction. The tire spun the 3/4" edge of the plywood deck. This was a very old revolve that I discovered was not a perfectly true circle and the side rim drive still never faulted. It did cause a lot of problems with the stairs that were built to line up flush to the edge of perfect 20' circle, but thats a different story.

Cutlunch, you're right about the resistance being pretty negligable inside the connector but DMX 512, being the fickle mistress she is, can be problematic from the resistance of plugging 2 cables together. 9 out of 10 times it will work under the worst conditions (mic cable, and long runs comprised of multiple cables) but will sometimes, for apparently no reason, fail because of something you can usually get away with. So if anyone does build a rotating DMX connector I'd like to know how it turns out.

Props on the carps skill Van. I would probably end up with an oval if I attempted it in wood.

 

[icewolf08]

Just thought I would toss in my 2 cents here. Here at the Pioneer Theatre in Salt Lake City we have three shows this season that are using revolves. So we have some experience with setting them up.

Two of our revolves are rim drive by friction, and one is a center drive (due only to space limitations). By far the friction rim drive works the best. If you have the room in what you are building to have a pinch track along the outer circumference of the revolve then you can mount your motors under the revolve with two wheels that pinch the outer rim of the revolve giving you the best traction. Our revolve, which was on the order of 20' in diameter was driven by 2 10HP DC motors on opposite sides of the revolve. The first time we used this setup was with a "dead-man's switch" type control where the max speed was set by the power inverters. It works fine, you just have to teach your operator when to let go of the button to hit each spike.

As for passing power/data up your revolve. Having dedicated commutators at the center is by far the best. But if you have to, you can wrap up your cables as long as you unwrap them in the end. For our current revolve, we have to wind cables up, so our preset position is wound in the opposite direction some so that we never wind the cables too much.

If you are interested in motion control equipment you may want to look into the "Make it Move" system at www.creativeconners.com. They have designed a motion control system that is affordable to people who don't have the giant budgets of commercial productions. Their system will read position information from incremental encoders, provides multiple E-Stop options, and computer control of any motors you choose to use.

 

[lxkev]

Hello

I've got to build a 6 meter wide revolve.. It has 2 be powered.....

The plan...... Batterns with caster on them....fixed to stage....revolve spins on top.... like www.dxarts.washington.edu/courses/490Form/readings/revolve.pdf

I want to friction drive the revolve..... But my big question is what motor do i use?????? and how do i fix a wheel 2 it......

I was looking at Electric Motor, Single Phase, .55Kw, 3/4HP, 2800 rpm. on eBay, also Motors Servos, Components Supplies, Electrical Test Equipment, Business, Office Industrial (end time 14-Mar-09 12:53:58 GMT)

Please note im from england...