On Wed, Jun 26, 2013, at 05:29 AM, Erik Christiansen wrote: > On 26.06.13 01:30, Gregg Eshelman wrote: > > 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. ;-) > > Careful; 200 pound chandelier x 1.5g deceleration = 300 pound force. > > By the time that a visually acceptable sharp deceleration is achieved, > and a good safety margin is allowed, we might be up around 6000 lb or > more? >
Exactly! I was thinking about that last night while walking the dogs (after I sent my earlier message). Some numbers: suppose you start with it 20 feet above the stage, let it "free fall" until it is 4 feet above the stage, then decelerate to a stop at stage level. First the free fall. Gravity is 32 feet per second squared. That means in the first second it will go from zero to 32 feet per second and fall 16 feet, winding up 4 feet from the floor. To bring it to a stop in four feet would require decelerating at 128 feet per second squared, and it would stop in 0.25 seconds. That deceleration rate is 4 gees, so if the chandelier weighs 200 lbs, you will need 800 lbs of force to do the job. At the beginning of the decel, you have 800 lbs of force and a velocity of 32 feet per second. That is 25,600 ft-lbs per second. One horsepower is 550 ft-lbs per second. So you need a 46 horse power servo to do the braking electrically. Not gonna happen on any reasonable budget. The force at the pulley is higher than the cable force. If the cable turns 90 degrees at the pulley, it is 1.41 times higher, if 180 degrees it is double. So the 800 lbs becomes 1100 to 1600 lbs. That is half to three-quarters of a ton. So you need a very strong pulley, and a very strong place to anchor it. If you would be nervous hanging a car from your anchor point, you better not hang your chandelier on it. I think the very first thing you should do is try to figure out how to make the chandelier as light as possible. It is a stage prop, not a real article. Can it be made from materials that are lighter than brass and glass? Can you use bright amber LEDs for the "candle" flames? Can you make the prisms out of clear plastic? Can you stylize it a bit? Maybe a very light frame, LEDs inside, and artfully folded and arranged clear or silvery (or both) mylar film to get the same "gilttery" effect? I think some out-of-the- box thinking could make a "chandelier" that weighs 10 or 15 pounds, which would completely change the nature of the job. Good luck! Let us know what you come up with - this is an interesting challenge. -- 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
