On Tue, 6/25/13, Bruce Klawiter <bmkl...@yahoo.com> wrote: Subject: [Emc-users] OT, Programable winch design, need help To: "Enhanced Machine Controller (EMC)" <emc-users@lists.sourceforge.net> Date: Tuesday, June 25, 2013, 9:03 PM 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. ------------
What you've described is essentially a descender rig, which has replaced airbags for almost all falling stunts in TV and movie production. Hook up the actor, he jumps, acts like he's falling and just before *splat* the descender quickly slows and stops. I did a quick search for diy descender rig and homebrew descender rig, didn't see anything that looked like a how-to. Guess either nobody has made their own or if they have... pesky liability issues even with "Don't try this at home!" disclaimers. Look up level wind winches. How fat is your wallet? They're overgrown versions of bait casting reels with a diamond screw system that runs a guide back and forth to keep the cable winding level. If you're near a coast or large/deep lake you might find a deal on a used electric downrigger. Load it up with 300 pound test line and there's your mechanicals, just need to figure out how to brake it to a stop at the right moment without breaking things. ;-) They usually have some kind of spool rotation counter so you can figure out how much line has payed out, which varies depending on line diameter since larger line changes the diameter of the wrap faster. I can think of a few ways of controlling the drop. One is with a paddle that rides in the spool, running on top of the cable as it unwinds. When the diameter gets down to the right level the paddle trips a switch, activating a mechanical brake or other control system to quickly slow and stop the motor. Repeatable control requires the cable to wind up level without crossing up and making lumps. Another is active sensing. Put a sensor on the chandelier and a wireless transmitter (like an XBee) that sends the 'touchdown' signal to the control system to brake the fall. A simple way to make the sensor is with a metal rod inside a plastic tube with a metal washer on top of the tube. That makes a normally closed switch. Attach something to the bottom of the rod so it's the lowest thing, will hit the floor first. You'll want to have the system setup so that once the touchdown switch opens it cannot go back to fall mode without a manual override, the button to raise it. It's a bit like the sensor the Apollo lunar landers used to detect when they were at the right height to shut off the descent engine. Simple and robust, extremely unlikely to fail... but only single use. I assume you'll want yours to last for more than a single performance. ;-) Yet another way is a colored marking on the cable and an optical sensor. To set the mark's position, lower the chandelier manually until it's just off the floor then mark the cable, I'd put it at the end of the downrigger arm. The ideal location for the mark and height of the chandelier when the mark is sensed would depend on how fast the braking system can slow it to a stop. I assume you want it to appear as if the chandelier has come loose and fallen free to crash on the stage, with appropriate smashing sound effect? This looks interesting. Controlling things from a DMX lighting system. http://bruce.pennypacker.org/category/theater/ Having a vision of a programmed lighting ramp that goes bright then quickly fades to off, with the chandelier dropper using the the varying voltage output to the light as the motor control input. ------------------------------------------------------------------------------ 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
