On Wed, 2013-06-26 at 09:53 -0400, John Kasunich wrote: > > 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. > > Maybe think of it as a model airplane structure. Balsa, and very low drag so it falls fast. At worst laminated birch ply like a EAA wing form.
Dave ------------------------------------------------------------------------------ This SF.net email is sponsored by Windows: Build for Windows Store. http://p.sf.net/sfu/windows-dev2dev _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
