Priority number one needs to be safety. Lifting 200 lbs is not a big deal. Lifting 200 lbs when people might be underneath is a very big deal. If something breaks and it drops 16 to 25 feet it could kill somebody.
Maybe you already know all this stuff - in that case, please don't be offended. Better safe than sorry. Does the stage already have a fly system? Even if it is manual, having the pulleys and counterweight system in place simplifies things a lot. In any case, I would strongly recommend counterweighting the chandelier. Hang two strong pulleys in the fly loft, one where you want the chandelier, and one backstage or in the wings. Run a cable from the chandelier to the first pulley, then the second, then the counterweight. Make the counter weight maybe 10-20 lbs heavier than the chandelier, so the chandelier will naturally want to go up. Then to drop it, use the motor to lift the counterweight. That way, if the motor fails, the chandelier goes up. The counterweight will fall, but you can locate it in a spot where it can't hit anyone. Everything should be ridiculously strong and overbuilt if there is any chance of people under the load. Breaking strength of all cable, fittings, pulleys, and rigging should be at least ten times the maximum expected load. Use as much redundancy as possible. Pulleys should be hung from the ceiling from strong structural members, using two independent methods of attachment. One that bears the load under normal conditions, and a backup (such as a loop of chain or steel cable) in case the first one breaks or comes loose or slips. The backup loop probably should pass below the actual lifting cable, so even if something crazy happens (like the pulley axle failing), the cable will still be caught by the safety line. Ideally you would never let it be above people at all. Perhaps you can drop it at the very front edge of the stage, and instruct the cast to never enter or cross that spot. Be very cautious about lifting and especially holding any significant weight with a servo. If the drive shuts down or trips out for any reason, the weight will drop unless the motor has a brake, AND the brake is properly interlocked with the drive, AND it works correctly. Holding a weight stationary is typically harder on the drive and the motor than making the same torque while spinning - that just increases the risk that the drive might overheat and shut down. My gut tells me that it will be very difficult to slow the "falling" chandelier without it being very obvious. The mind knows what a falling object should do, and is pretty good at detecting "unnatural" behavior. The control can be done in HAL if you want. It isn't hard to set up a servo loop with a PID controller. The position command could come from hal-streamer, which would let you define a position vs time profile using something as simple as a spreadsheet, and play it back exactly as many times as you want. You could experiment with different profiles to try to get something that looks as natural as possible. Making the cable wind evenly side to side can be done with a level wind mechanism. If the cable is short and thin and the drum is wide it can be a simple threaded rod 6 inches or so in front of the drum that is belted or geared to the drum, and moves a guide across the drum. For example, assume you are using a 1/4" cable, and your drum is 4" in diameter. One turn of the drum means 4 times pi = 12.56 inches. Call it a foot. To handle 25 feet of line, you will have 25 wraps on the drum. If each wrap is 1/4" and you want to have a single neat layer, then the total width of the drum needs to be at least 25 times 1/4" = 6.25 inches. If your level wind uses 3/8-16 threaded rod, it will take four turns of the rod to move the cable guide 1/4". So the threaded rod needs to turn four times for every revolution of the drum. Small timing belt pulleys would work for that. A couple years ago I built a system somewhat like this. I was lifting a much smaller load - a prop that weighed less than 10 lbs and was bulky and rather soft - so I didn't have the same safety concerns. I used three winches with a kinematics module in HAL so I could control the prop in three dimensions over a fairly large working envelope. I was using kevlar line that was about 0.035" in diameter. I used 1/4-20 threaded rod for the level wind, geared roughly 4:5 with the drum. So the 0.035" line wound onto the drum at about 0.040" per turn. The drum was over a foot long, so I could fit at least 300 turns on it. The drums were made from 4" schedule 80 PVC pipe with plugs for the motor shaft on one end and a bearing on the other. The OD of the pipe was about 4.5", so when completely wound up I had over 350 feet of line on the drum. The motors were some beefy NEMA 42 steppers with microstepping drives. Even with my much lighter load, powering down the stepper drive would allow the string to unwind and the load to drop, Here is some testing of that system: http://www.youtube.com/watch?v=uVdXyU4W5dQ On Tue, Jun 25, 2013, at 11:03 PM, Bruce Klawiter wrote: > I need help to get me started on this. > The winch is to drop and raise a chandelier for the local high school doing > Phantom of the opera, I am building the chandelier and would like to build > the winch also. > The chandelier I'm guessing will weight 200 pound and the winch can be 120 > volts > I would like to drop, free fall the chandelier 16 to 25 feet then in the last > foot or so arrest its fall so it crumples on the stage without actually > crashing into the stage floor, then raise it back up slowly. > I'm thinking I could just attach a spool to a servo motor and unwind the > cable really fast, some question I have would be what motor, how do I size > the motor, what controller that's easy to program, how do you guarantee the > cable does not get tangled up, how do you make the cable wind up side to side > on the spool. > Any help or ideas I can get on this project or if you can point me where i > can go to learn or get help will be greatly appreciated. > > Regards, > Bruce > > ------------------------------------------------------------------------------ > This SF.net email is sponsored by Windows: > > Build for Windows Store. > > http://p.sf.net/sfu/windows-dev2dev > _______________________________________________ > Emc-users mailing list > Emc-users@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/emc-users -- John Kasunich jmkasun...@fastmail.fm ------------------------------------------------------------------------------ This SF.net email is sponsored by Windows: Build for Windows Store. http://p.sf.net/sfu/windows-dev2dev _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
