Perpetual Motion Machine?

Hello everyone. I've decided to build a revolve that will be lightweight, easy (ish) to assemble, disassemble, and store, and that will allow for casters to be either floor or revolve-mounted, and that can powered by an electric motor, if one wishes (leaving room for chain or cable.) But for my first use I'm hoping to abandon the motor and use human power to turn it: specifically, the actors, of which there are three. No set, just the actors, three small chairs and a small table. Here's the question (please be kind) - for those of you who have built your own revolves and have real-life experience: if the actors get it going at a reasonable clip (average playground merry-go round clip, fast, but not dangerously so), and if I lubricate the stuffing out of it, and keep if exceedingly plumb and level, etc. etc., as a practical matter how long might I get it to spin once it reaches the desired acceleration? The actors will hop on once it gets spinning. Diameter 18 feet, total weight, with actors, what? - 800 to 1200 lbs, I would guess. How much friction will the casters create? Should I use a central bearing? Have I really thought this through? Of course not! Why would I mess this up with clear and rational thinking?
 
My thought would be too much weight + too many points of contact. Merry go round has one central axle so you only have friction at the one spot. There are just too many places for the friction to slow it down. Take one of your castors and spin it. How long will it spin before it stops? translate that distance to the outside diameter of the revolve and I would think one or two rotations max.

This is wholly theoretical for me as I've never worked with a revolve, but I feel like the level of engineering required to make this work well and with any modicum of safety would be cost and time prohibitive.
 
My thought would be too much weight + too many points of contact. Merry go round has one central axle so you only have friction at the one spot. There are just too many places for the friction to slow it down. Take one of your castors and spin it. How long will it spin before it stops? translate that distance to the outside diameter of the revolve and I would think one or two rotations max.

This is wholly theoretical for me as I've never worked with a revolve, but I feel like the level of engineering required to make this work well and with any modicum of safety would be cost and time prohibitive.
I looked at playground carousels, TheaterEd, and was really amazed at thier simplicity - a post with two cups, a ball bearing, and lots of grease (simply put.) That's a lot of spin for the price, and the weight helps with the inertia once the thing's in motion, but your point is well-made: one pivot point verses many contact points. I wonder if metal conveyer-type casters on a metal chase might not help? Or using the central privot with the casters just "kissing" the underside: enough to keep the thing stable (thinking aloud here...) That is, split the difference between the casters and a center bearing (even if its a bearing device on an axel, like an automotive wheel). I still have a few weeks to deliberate, but time is marching forward. If I can engineer this wheel to move smoothly enough, then the the actors can keep in spinning for as long as they need (I haven't expained how they're to spin it, but they will be standing and moving along a stage raised to match the plane of the revolve.) I had better give some casters a spin test, though, as you suggest.
 
Any professional revolve I have seen had not the casters on the ground, but mounted solidly to a frame (inverted) so that the stage floated on them. This way, they do not rely on the smoothness of your stage to operate properly, and they also won't damage the floor or get things caught in them. You will however need to come up with a good, smooth track under the revolve floor for them to travel. Be sure to use fixed axis -- none of those swivel casters.

Just food for thought.
 
All of the above is true, so thank you all. The guys here at the shop are determined to make a central bearing device of some sort. Don't know why - I think they just like going to the junk yard. The great thing about bouncing ideas around in Control Booth is that it lets you toss a handfull of ideas into a sifter to see what shakes out. The revolve will be built, and I'm starting to focus on what's practical and important, so keep the ideas coming. It won't spin forever, but I'm starting to get some clarity....
 
Just make extra sure that the actor's safety is being accounted for. It may just be that I am not picturing it correctly, but it sounds like it would be pretty easy to walk or jump onto the revolve and throw one of the other actors off balance. What level of theater is this for? I would be quite nervous with this rig in a high school.
 
Just make extra sure that the actor's safety is being accounted for. It may just be that I am not picturing it correctly, but it sounds like it would be pretty easy to walk or jump onto the revolve and throw one of the other actors off balance. What level of theater is this for? I would be quite nervous with this rig in a high school.
Yikes! That's really something I've not considered at all, actually, TE, so thanks again. This configuration is strictly for two/three mature adults, well-rehearsed and the rotation sparingly used. The revolve is actually just the central cog in a sort of literal deus ex machina that sets a chain of mechanical and electrical things in motion. I have included, as I've said before, a motor drive, but the chain would actually get in the way of this particular effect, which is why I want to can the motor for this show. Moreover, thematically, this is about men moving things - creating things - sometimes dangerous things... about humans pushing boundaries maybe too far, about the joys and horrors of our contraptions. I'll put on the motor if I have too, and run it safely from the control booth, but I trust the actors with this (I think. Do I?) I'll for sure consider it, as well as everything else you offer up! It also occured to me (after weeks - months now) of thought and research, that everyone who's built a revolve and talked about it online has designed it to be driven by some continuous means, either motor or human, and that this continuous force applied meant that, although friction and spin length weren't ignored, they weren't at all critical. Leave it to me to make friction reduction the main consideration. Just a few days left and we have to come to a firm decision and start designing.
 
It sounds to me like you'll be alright, just make sure to have some sort of lock / brake that the actors can operate.

Main reason I thought of it is that I had a kid run and jump onto a scenery wagon on the last show and slide the sucker a couple of feet. Lucky for me all the other actors were sitting down so no one fell. Added an extra brake and changed the blocking a bit and we were good to go.
 
I'm not loving the idea of getting this thing to anywhere near playground carousel speed. There's a reason they don't put those on playgrounds anymore. There's the danger of losing your balance and falling. But there are also going to be pinch points between the revolve and the deck. What happen if an actor gets a shoelace or pants cuff caught in the crack as it's going full speed? A motorized system would have a technician with line-of-sight to the action on an e-stop.

My opinion: this effect requires a stunt professional to design and train. Or use standard methods with standard safety procedures.
 
I'm not loving the idea of getting this thing to anywhere near playground carousel speed. There's a reason they don't put those on playgrounds anymore. There's the danger of losing your balance and falling. But there are also going to be pinch points between the revolve and the deck. What happen if an actor gets a shoelace or pants cuff caught in the crack as it's going full speed? A motorized system would have a technician with line-of-sight to the action on an e-stop.
Good things to think about. Is 4 rpm at 18 diameter playground speed? It does seem very fast, now that I walk it out, especially at that weight: a lot of torque to stop it. Funny how we've moved from "will it turn fast enough and long enough" to "will it turn slow enough and stop easily enough." Well, I'm thinking (aloud, again) that easy turning is better than the opposite, and that the actors can manipulate the spin to a safe and comfortable level, for sure. The gap is another matter, and I think you're right: it needs careful attention.
What really amazes me is that I work with a lab that spin-tests gas and fluid measuring devices and it never occured to me to spin test the casters until Theater Ed mentioned it. So today we drove and walked around with a stopwatch spinning every caster and cart wheel we could find and wow, is there a marked difference between them all! Some tested as high as 118 seconds (and these were on older buggies), others as low as 5 (of those that spun: some were stuck). The 118 was impressive: it was on a Family Dollar cart. Even a Rockwell (now Sensus) turbine rotor for Natural Gas measurement rarely spins that long in a windless room when zapped with an air gun. In any case, if I begin by focusing on friction and spin time I can ultimately transition to power management knowing that my device requires the minimum affordable effort to spin, which is really my ultimate goal. And if it can be easily manipulated by human power, that will save us from having to use the motor and chain unless we absolutely need it. Thanks again for the line of thought, especially safety. i think you just saved me several days work and a few $$.
 
Good things to think about. Is 4 rpm at 18 diameter playground speed? It does seem very fast, now that I walk it out, especially at that weight: a lot of torque to stop it. Funny how we've moved from "will it turn fast enough and long enough" to "will it turn slow enough and stop easily enough." Well, I'm thinking (aloud, again) that easy turning is better than the opposite, and that the actors can manipulate the spin to a safe and comfortable level, for sure. The gap is another matter, and I think you're right: it needs careful attention.
What really amazes me is that I work with a lab that spin-tests gas and fluid measuring devices and it never occured to me to spin test the casters until Theater Ed mentioned it. So today we drove and walked around with a stopwatch spinning every caster and cart wheel we could find and wow, is there a marked difference between them all! Some tested as high as 118 seconds (and these were on older buggies), others as low as 5 (of those that spun: some were stuck). The 118 was impressive: it was on a Family Dollar cart. Even a Rockwell (now Sensus) turbine rotor for Natural Gas measurement rarely spins that long in a windless room when zapped with an air gun. In any case, if I begin by focusing on friction and spin time I can ultimately transition to power management knowing that my device requires the minimum affordable effort to spin, which is really my ultimate goal. And if it can be easily manipulated by human power, that will save us from having to use the motor and chain unless we absolutely need it. Thanks again for the line of thought, especially safety. i think you just saved me several days work and a few $$.

That speed works out to ~3.75 feet/sec at the circumference. Way too fast to be able to be safe, even with E-stops.....in my opinion. Just think of the centrifugal forces involved with a ~150lb man standing on the edge or near it traveling at that speed.

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Without being under load, I don't think those spin tests are telling you much. You'd want to load the caster and see how much force it takes to get it / keep it rolling at the desired velocity.

Back to safety, a little googling indicates that airport walkways move at 1.2 ft/sec. Seems a good benchmark for how fast you could go at the perimeter without needing specialized stunt training. In my opinion. Then you'd better calculate how much force it would take to stop that thing on a dime, and if it's enough to break a bone, you better have some kind of E-stop and brake.
 
^ No doubt you guys have got me thinking hard about this. No one has even mentioned turning around and walking on it while it's spinning, which was my intention. I have (in my mind) slowed it down to 2 rpm or less, which is about walkway speed (without the centrifigal force), and it still seems fast now that you all have weighed in. My motor/gearing mechanism will turn the revolve at a maximum rate about .8 rpm, which seems a snail's pace by comparison, but much safer. Well, thanks everyone for keeping me grounded in reality. [On the spin tests: If putting a 180 pound man in a Family Dollar buggy (about twice the weight-to-wheel ratio as the planned revolve, loaded) and pushing him across a smooth concrete floor at high speed isn't a viable test, then I don't know what is.]
 

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