My big question now is what would be the most efficient way to control the
turntable... I would like to keep it simple so that my students can learn about electricity and electronics,
wire it themselves, and not have to worry about writing computer programs.
My 1st thought was just simple SPST switches, DPDT switches, and a
potentiometer. This will obviously be easy, but not consistent with the RPM.
Any thoughts?
Icewolf08... I will be contacting you. Thanks for offering your help.
I know that you may be contacting me by other means, but I figured I would give a head start here. First, I have to agree with Footer, friction drives just don't cut it. That was what was originally designed for our production of Mis, and it couldn't last 81 performances, and was always more trouble that it's worth.
Now, it sounds to me from everything else you have done, that your "high school budget" is significantly more substantial than many high school budgets. In any event, Mis is a phenomenon and will sell out every night you perform it, so you should make plenty in ticket sales. So, that being said, I think that it is worth investing in the
purchase or rental of a motion control
system. Before last season, everything with automation here was done via dead-man's-switch, limit switches, and setting speed and acceleration on the
power inverters. Running a major show is a very bad idea without motion control they learned. First off, it is almost impossible to be consistent in where everything lands every night. Second, if your
switch gets stuck or you have a short in your
switch box or
potentiometer then your motors just go until something gets in their way. We actually had major problems during tech for Beauty where the
revolve started going on it's own due to a short, and the couldn't get it to stop until it had ripped through a
drop and tied up almost the entirety of the
stage.
I don't know how you are fixed in motor land, but to drive a
turntable as big as yours, you are probably going to need a big honking motor, probably on the order of 5hp. So you are going to need some serious
power to drive it, as most motors that would fit the bill to drive your
revolve will want 208v or 230v.
The very best way you could set up your drive
system would be a direct gear drive, this is probably also the most expensive. You would need a ring gear that was the same diameter as your
revolve. Then connect motor to gear reducer to
revolve all direct (no chains or cables), this will allow for virtually no slipping in the drive
system, give you very accurate
encoder readings, and probably the least number of problems. This will also give you an infinite rotation.
The next best way would be a
winch and cable drive. This would require you to
build your evolve with a sturdy outer ring, probably steel, that you can wrap the cable around. You probably want to make two wraps around the
revolve for best
grip and least slip. You also need a way to tension the cables once they are attached to both the
winch and
revolve. Due to this tension, you need a very secure
revolve center so it doesn't
shift. Since
wire cables will stretch, you will need to keep an eye on it every night and re-tension the
system. This
system should give you minimal slippage, but you have a finite distance you can move the
revolve if you are using a
winch drum with canted grooves, though that is the best option for
winch drums in this situation.
Last option is friction drive. This is a doable solution, and possibly the least expensive. There are many ways to approach this drive
system, each will have the same flaws in slipping and issues with tire pressure,
etc. The best way to do any friction drive is to have at least 2 motors, to balance the
system. You could set them up so that you have a vertical tire driving the
revolve from below, or you can put a steel ring around the
revolve and drive from the side. If you drive from a ring on the side you can use two tire to pinch the ring and drive it. These systems are going to show the most slipping, and be the least reliable.
I have worked with all three systems, and I know people who have worked all three systems, and hands down the direct drive wins, with winches in second. You could do a cain drive, which would be a variant on both the direct and
winch drive, that would work well, but you would need a lot of chain.
Next of course you need a way to control all this. I would suggest, as I have before on these forums, that you look into the "Make it Move"
system by
Creative Conners Inc. This is a motion control
system that is designed to be simple to use and fit in the budget of many small theaters. Their gear is also available for rental. The offer training, consulting, and
system design help as well. Garreth Conner is a very nice guy, and is happy to help where he can.
Hopefully some of that is useful. I haven't written a post like that in a while. Hopefully it doesn't break any of the TOS, but I didn't really tell you how to do anything, just the basic ideas, and it sounds like you have a pretty engineering oriented mind anyway, so you probably know half the things I just said. Anyway, feel free to contact me with more questions.