Revolve zero position - why?


I am working in China at the moment commissioning a new automation system here. They have, amongst other things, a revolve built into the rear wagon. As I cant speak the same language as anyone else onsite I cant find out why there is a limit switch that marks 'zero' position.
The machine has an encoder and I can tune it in degrees or millimeters or what ever so why wouldn't the operator just be allowed to 'move up 180' or 'move down 720' - who cares where 0 is? As long as it really turns 180 degrees when asked why not just use the position it is in on the day of the bump-in - irrespective of the position reading. Mechanically there is no reason it cannot revolve infinately so can anyone thing of a good reason to have a zero position marker - and would you want me to stop the machine there or just let you know it has past that position with an indicator on the operator interface? Or should I just ignore it?
Any thoughts welcome. Cheers all.
I would guess its for degrees past that point. Lets say there is a chair on the turntable. The chair needed t oroutate t ofo ur differnt positions over the course of the show, sure you could base each move off of the current position, as in position three is 260 degrees from position two or you could refrence the home. The only advantage that I can see is if you need it to run out of order for some reason you sill still be able to hit your marks.

If its still not clear I can try and repharse it.
Perhaps also it was done on the cheap in some way and there say is only in some way enough power cable to feed the thing to some extent before it becomes a wee bit over-twisted about the thing and torques it's way out of working.

Could be an interesting thing to find out more about.

Could otherwise zero position be the position where what is installed or put atop the wagon lines up with it's designated set position?
What is the top of the revolve made of? If it more then one peice maybe they want a zero position that the seams match the rest of the stage. The simple thing would be to get a translator, your company should pay for it. This is probably the best course of action as else it could blow up in your face with unecessary waste of time and money. With a translator you could explain your idea to them they may not have thought about it. Is this a completely new revolve or just an upgrade ? If it is an upgrade then maybe this is what they are use to. Is there space under the revolve for things like trapdoors that have to line up or let people pass the revovle understage? There is a million possible ideas.
Ok - so that was a spookily good response! Thanks all.
Firstly, Soundman, the control system allows either a 'move up/down' type move or a 'move to' type move so any of those scenarios are still possible without a limit switch. Ship, there are 3 static motors attached to the flooring around the outside of the revolve (driving it using tensioned friction wheels) so there are no trailing cables to foul up. Sure I can understand the need for a zero during construction but why during operation - especially as it has an encoder built into it the gives position and speed feedback to the operator? If, as an operator, I want it to go to zero - I just tell it to go to zero and away it goes - timber all lines up nicely and presto - so whats with the mystery limit switch?
Cutlunch - the surface is timber - sadly they didn't fit rubber between the steel frame and the timber so it will alsways ceak and groan abit but, that said, they've done quite a noce finish on it. Its only a single revolve built into a 350mm deep wagon - no traps (except service traps for the encoder etc) so that doesn't come into the equation. Its a brand new theatre with completely inexperienced operators so past experience doesn't come into it.
I'm only here because I worked for the control system company 5 years ago - before they sorta went out of business and seem to be the only person available to commission the bloody thing - as for my company paying for a translator - I am my company so it comes out of my own wages. No, its just one of those curiosos from commissioning that I thought I might get a second opinion on from a few of you folks to see if I could straighten it out. The mystery remains!! Gotta love a mystery!
Tomorrows challenge is to get 8 side stage wagons (4 each side) to run onto stage but not into each other when the designer DIDN'T put a limit switch in - the fun continues
The other thing you guys should remember about designing your next revolve is the resolution of position. The guys here want it to be measured in degrees. As it has a circumference of about 29000mm that means accurate stopping anywhere within about 80mm of target - so it is better to work in smaller increments like millimeters or at least allow it to be set up with 3600 or even better 36000 instead of 360 - just a tip. Cheers
My two bits: Maybe they wanted independent verification of the position, say at the start of the show or at some other time when the operator cannot see the turntable position. (I’m assuming that at the start of the show, the turntable is in the “zero” position.) Even though the controller directed the turntable to turn through specified arcs, say 90 degrees, then another 90 degrees, then back another 180 degrees, the actual motion may be slightly off and could add up over several sequences.

Or maybe as a way to “recalibrate” the turntable position if they can’t actually get someone to the turntable and/or readily communicate with someone at the turntable.

solelly so you can control it. much like robotic lights it has to have a place to start from that way when programming the revolve each posistion has a certain numer assigned to it. without zero it would be impossible to program.
I agree it is from a programming perspective, you need to know the point of origin, and having a zero position allows you to reference everything from that position. It also means that people using it also have a marked reference position. There also might be a time when someone remotely without being able to see it needs to set it to a specific position, where again, being able to determine position based on relative to the zero position would be important


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