Turntable? Not another one...

T

Thefoxygranpa

Active Member
Hello all

Doing a production of Les Mis this summer, looks like turntable is up in the air as a possibility to happen. Going to be in a small blackbox, but I have enough space for a 17' revolve. Going to be building up a stagedeck obviously. Going with the whole upside down casters and two layers of ply on top probably. Lots of thanks to Van for his drawings he posted!

The pickle is coming in at the automation part of it. This might get close to TOS violation so I'll let mods decide.

[media]http://www.youtube.com/watch?v=oEgqLv18_0E&feature=player_embedded#[/media]

Is almost exactly what I'm looking for. He explains details of equipment being used at the beginning of video. My questions are...is that large of a motor necessary? 3phase 2hp is quite a beefy motor.

Also, chain-drive or direct friction? Pros/Cons of each?

Any questions just ask! Thanks in advance!!!

-Evan
 
Chain drive or cable drive is the way to go, warping either around the circumference of the revolve. Friction drive can work well but the motor/drive has to has to be designed for it and that takes a bit more then just an old tire and a chain. I have seen revolves ran with 1hp motors. It depends on how much weight you are putting on it and what kind of reducer/gearing you have on it.

If you are trying to do this from the ground up and don't have a motor, VFD, and a Goddard I would suggest you rent from Creative Conners. They have essentially a turnkey solution to get you up and running fast and safely. Chicago Scenic also has a great automation department that can help you do what you need to do.

I can guarantee you can rent their system for a 1/4 of the cost of building a proper system.
 
The amount of power you need to apply to the revolve depends on the mass of the revolve and everything on it, the distribution of that mass, and how quickly you want to accelerate it. Mechanical Design for the Stage has the forumlas you'll need to calculate the required force, which combined with speed will give you power. Remember that in physics terms, acceleration is any change in velocity--speading up, slowing down, or changing direction--so calculate stopping power the same way.

Required motor power is the above figure, plus drive transmission losses plus drag on the revolve itself.

The disadvantage to chain drive is that the tensile forces (the critical factor for chain) required to transmit large amounts of force can get pretty expensive. The downside to direct friction drive is that it can be hard to acheive adequate friction and it requires a wide face on the revolve to drive against. There's also cable drive to consider. The pros and cons of these are all laid out in the book, I'd highly recommend you get it and study it thoroughly before making any other decisions.

And of course, don't forget to include E-stop systems (make sure you design the system to withstand a rapid E-stop!), hold-to-run switches, and above all, make sure that the system is truly fail-safe.
 
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Rental is still an option at this point, but leaning towards building from the ground up because it may be able to be used for a variety of shows upcoming.

With a 20:1 reducer on the motor should get me ~88rpm at the gearbox...so what would I get max rpm? at the 17' diam revolve? Also if someone could show the math involved my mind would be at ease.

Pricing out ansi #40 chain and sprockets...fun.

Edit: Thanks for the link to the book, ordered it now!
 
Thefoxygranpa said:
With a 20:1 reducer on the motor should get me ~88rpm at the gearbox...so what would I get max rpm? at the 17' diam revolve? Also if someone could show the math involved my mind would be at ease.
Click to expand...
Ha!

That part is the most fun!

What you really do with these type of things is start with how fast you want it to spin and how much weight you are going to put on it and work backwards, unless you already have the motor.

I doubt you are going to want this thing to spin any faster then about 3rpm.

Also keep in mind that controlling a motor safely is pretty involved. If you have experience working with industrial automation components its not too hard to do, but there is a learning curve there.
 
Footer said:
Ha!

That part is the most fun!

What you really do with these type of things is start with how fast you want it to spin and how much weight you are going to put on it and work backwards, unless you already have the motor.

I doubt you are going to want this thing to spin any faster then about 3rpm.

Also keep in mind that controlling a motor safely is pretty involved. If you have experience working with industrial automation components its not too hard to do, but there is a learning curve there.
Click to expand...

Hmmm let me think about how much weight is going on and all and I'll be back tomorrow. And thankfully my father has automation experience! His knowledge will be pulled on definitely.

Thanks for all your help already
 
Thefoxygranpa said:
With a 20:1 reducer on the motor should get me ~88rpm at the gearbox...so what would I get max rpm? at the 17' diam revolve? Also if someone could show the math involved my mind would be at ease.
Click to expand...

The missing piece of information is the diameter of the drive wheel (that may not be the proper term) off the gear box that is turning at 88 rpm (revolutions per minute or rev/min).

For the sake of discussion, assume that it is 2 inches in diameter.

The circumference, C, equals pi times the diameter:

C = 2 inches x 1 foot/12 inches x pi = 0.52 feet
So one revolution (rev) travels 0.52 feet.

At 88 rpm, the drive wheel will move a belt at:

Belt speed = 0.52 feet /rev x 88 rev/min = 46 feet/min.

Next, the circumference of the 17-foot diameter turntable is:
C= 17 feet x pi = 53.4 feet, and one revolution will travel this distance.

The outer edge will move at the belt speed, so the turntable revolve rate in rpm is:

46 feet/min x rev/53.4 feet = 0.86 rev/min (rpm)

Again, the "drive wheel" diameter is needed to estimate the turntable speed.


Hope that helps.

Joe
 
Okay...well a couple more details to further this.

Max 7000lb on platform. Includes lumber, scenery, actors, etc. Though I doubt it will ever be at this, still working on that.

Sprockets I'm looking at are 2.003", so close enough to the calculations above for government work...

Only .83rpm?! Yikes, I guess I'm looking for a full rotation every ~25-30 sec? 2-2.5rpm max I suppose. Am I being over ambitious with that fast of a revolve? When talking to a higher up their response was "as fast as it was on broadway."

Hm time to look at other gearboxes?
 
You can play with the combination of gearbox and drive sprocket to get close to the right ratio. In your case, just going to a 6" sprocket would get you the speed you want. You can also add an additional reduction stage between the gearbox and final drive chain (which can sometimes make the tensioning mechanics easier. I don't really like what the guy in the video did).

Don't forget that your gearbox will need to meet your horsepower and torque requirements, so shopping for gearboxes now is a bit premature until you figure out your power and force requirements.

Also, a few things to take into consideration when selecting a motor:

* Running below rated speed can be hard on motors. Consider spending a bit more to get an Inverter-rated motor--they have heavier windings and better cooling fans to better deal with low-speed operation. You can also get separate blower kits that cool the motor independently of shaft speed if you anticipate running the motor at low speed for extended periods of time.
* Especially since you'll be mounting the motor below a deck, go for a TEFC (totally enclosed fan-cooled) motor--they're much less susceptible to dust than open framed motors.
* Not all motors are designed for bidirectional operation, and it all comes down to the fan design. There are a couple of different fan designs, and not all of them work in both directions. Make sure you select a motor with a bidirectional fan (or fit it with a blower kit as mentioned above).
 
ajb said:
You can play with the combination of gearbox and drive sprocket to get close to the right ratio. In your case, just going to a 6" sprocket would get you the speed you want. You can also add an additional reduction stage between the gearbox and final drive chain (which can sometimes make the tensioning mechanics easier. I don't really like what the guy in the video did).
Click to expand...

Yeah the whole chain running along those pieces of lumber for tension, was not liking it. Was thinking two idler sprockets for the chain to run on.

Couple more things, the motors I am looking at are TEFC and electrically reversible...
 
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I don't think your gearbox and motor are directly compatible. The gearbox specs indicate that the input face is 182TC with a diametric bolt spacing (ØLA) of 7.25", and the motor is 56C frame with a ØLA of 5.875". Looks like the -005 and -010 are the exceptions here, the rest of the 262 family is 56C. You're matching a 2HP motor to a 4HP gearbox (which is better than the other way around!); you'll probably have an easier time if you look at 2HP gearboxes. If you call around to vendors, I'm sure they can help you find a nice match.

But yes, the output shaft (ØS) is 1.125".

Also, I really strongly suggest you wait until you've had a chance to do the math on the required torque before buying anything. Distribution of mass is a huge factor in angular momentum that you'll need to calculate. You don't want to spend a bunch of money on this stuff and get it all set up only to find that you didn't buy enough HP.
 
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Every motor system I have built or have worked with on stage tends to use a SEW Eurodrive motor. You can pick up a 1hp to 4hp motors on ebay for a decent price with the gearbox attached. SEW makes some of the best motors out there. They are solid with great mounting options. I have a 1hp motor with a 20:1 reducer sitting in my storage unit just waiting to get put into a motor frame.... so if anyone has a cable drum, a few sprockets, 4 pillow blocks, and some angle iron and channel iron laying around that needs a home... let me know.
 
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ajb said:
I don't think your gearbox and motor are directly compatible. The gearbox specs indicate that the input face is 182TC with a diametric bolt spacing (ØLA) of 7.25", and the motor is 56C frame with a ØLA of 5.875". Looks like the -005 and -010 are the exceptions here, the rest of the 262 family is 56C. You're matching a 2HP motor to a 4HP gearbox (which is better than the other way around!); you'll probably have an easier time if you look at 2HP gearboxes. If you call around to vendors, I'm sure they can help you find a nice match.

But yes, the output shaft (ØS) is 1.125".

Also, I really strongly suggest you wait until you've had a chance to do the math on the required torque before buying anything. Distribution of mass is a huge factor in angular momentum that you'll need to calculate. You don't want to spend a bunch of money on this stuff and get it all set up only to find that you didn't buy enough HP.
Click to expand...

Thanks for that :oops: . Right now waiting on that book you recommended for me. I'm with you on waiting, heads would role if this doesn't work. :grin:

Edit...again.: Footer thanks for that! I'm all for used equipment and the fact it is a widely used named in motors. When looking at all of the SEW-eurodrive motors they didn't seem to have a 90 degree output. I guess that is a big part of what I'm looking for, or if I'm missing something I am all ears....thank you!!
 
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Thefoxygranpa said:
Thanks for that :oops: . Right now waiting on that book you recommended for me. I'm with you on waiting, heads would role if this doesn't work. :grin:

Edit: Footer thanks for that! I'm all for used equipment and the fact it is a widely used named in motors.
Click to expand...

Here is the BIG question...
What are you intending on using for control? A hot box, limit switches, some type of computer program? What type of safety system do you intend on implementing? Any time automation is used on stage, these questions are the hardest to answer and need answering first. I am really concerned because you are buying budget components you are going to skip over this step. I have seen automation run away from the operator because these issues were not taken into account. It can cause damage to the venue, destroy scenery, destroy the automation system, and cause injurys or death. Just because you are using this motor this time to run a simple revolve does not mean that next time it is use it would run a tracking wagon or to lift a piece of scenery. Budget safety and control systems in now.
 
Thefoxygranpa said:
Regarding safety and control. Is it unacceptable to use the VFD to control the motor? The operator will have a clear line of site to the turntable at all times.
An emergency stop will also be in place to ensure power is cut to the motor if any safety concern arises.
Click to expand...

Thats essentially what a hot box is. However, I think its a bit too difficult to run everything off the VFD for the show itself. VFD's are not made for the backstage enviorment. They are made to set up and be controlled externally. If you do go with the hot box option, set it up with a simple "forward", "backwards", E-Stop, and a pot for speed. I would highly suggest either putting in a dead man switch or two e-stops, one on either side of stage.

Idealy you would purchase a control system from Creative Conners, Hudson Scenic, Chicago Scenic, or Goddard .

Once again, for a revolve hard limits are not necessary. However, think about how you are going to adapt this system for the future. It will be used again and you want to have these things answered now so you don't have to buy more gear down the line or even worse go without the gear later on "because it worked just fine before".
 
It would seem I would be going with the hot box solution for control [running form VFD]. The VFD's I'm looking at have the ability to be programmed to do exactly what you described above.

It also has a serial comm port that I may take the time to make something to work with. It would have the very basic commands needed to run the revolve like you stated above [forward, reverse, speed/frequency, e-stop]. I would keep that with the operator and mount the VFD somewhere else then.

I will also design in E-stops backstage. This is a very small blackbox theater with slim to no backstage area...but I will make it happen to install e-stops back there as well. I really do need to post some pictures sometime so show it off, I'm pretty proud of the productions that are put on there. :p .

In the foreseeable future, and after talking with the exec. director of the facility, we see no use for it other than this turntable, and perhaps smaller ones later on. I'll do thinking tonight how I would integrate it otherwise and how it would work in other environments. The big picture is to expand the theater [either build entirely new space or expand current one] , and I would hate to have paid a lot of money for something that will not safely work in the future designs.

Edit: Oh look at these casters!http://www.grainger.com/Grainger/items/2LU83?Pid=search Now I wonder if they have around 80 or so in stock!
 
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The nice thing is that none of what you're looking at using will be useless in a more complex system. You can easily add an electromechanical brake or an encoder to your motor if a situation demands it, or a more complex programmable controller on top of your VFD. The concern that I think Footer was getting at was that down the road someone (not necessarily you, but maybe your managing director, or artistic director) could say "we already spent $X to automate that revolve, why do we need to spend $Y extra now to automate this wagon track?", without realizing that the safety concerns can be vastly different.

You can do a lot with a PLC and a VFD connected via Modbus, however, this introduces a whole new level of complexity not just in making it work, but more so in making it safe. And on top of that, it doesn't matter how thoroughly failsafe your PLC programming is if your underlying electronics and mechanics are flawed, so start from the ground up.
 
To add some authority to this thread:

NFPA 79 - Electrical Standards for Industrial Machinery Chapter 9 covers control circuits. 9.2.2 defines three categories of stop functions, and 9.2.5.3 covers when and how they are to be implemented. 9.2.5.4 covers emergency stops specifically. And there's lots more relevant info in that document that you should look at. You can read it for free if you register.

OSHA 1910.211-219 covers machinery and machine guarding. (there's less immediately relevant stuff here, but still good to read)
 
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