From: jmb184@servtech.com (John Bailey) Newsgroups: sci.math,sci.engr.mech Subject: Re: HELP on mechanism Date: 23 Jan 1996 02:16:10 GMT In article <4dpdlv$d5u@news.ox.ac.uk>, mert0236@sable.ox.ac.uk (Thomas Womack) says: > >Doug Huffman (dhuffman@mail.awod.com) wrote: > >: Yes, it is possible. Go to your blood services center and look at the >: phoresis machine (e.g., Baxter Fenwal 3000). It uses a centrifuge to separate >: blood fractions in a closed system simultaneously returning the depleted >: fraction to the donor. > >: Scientific American magazine published an article on the topology some years >: ago. With regard to the article, I attach the verbatim correspondence on the same subject which took place about nine months ago when I asked a question very similar to yours on the sci.physics news dl. The Thai dancer model is very worthwhile to act out. Depending on the constraints of a particular problem, the solution may turn out to be useless, but it is nonetheless interesting. What follows quotes the previous correspondence: From: IN%"billb@eskimo.com" To: IN%"jmb184@delphi.com" CC: Subj: RE: Help with SciAm article John, I think it was in the amateur scientist column. I can almost see the crosshatching of Stong's artist on that rotating platform... :) The secret was to take an incoming cable located on axis with the rotating platform, loop it out and around the platform, then back into the center of the opposite face. The loop of cable was then driven to turn twice as fast (or was it half?) as the rotating platform. The tradeoff was that huge loop of cable slicing through the air around the platform. .....................uuuu / oo \ uuuu........,............................. William Beaty voice:206-781-3320 bbs:206-789-0775 cserv:71241,3623 EE/Programmer/Science exhibit designer http://www.eskimo.com/~billb/ Seattle, WA 98117 billb@eskimo.com SCIENCE HOBBYIST web page To: IN%"JMB184@delphi.com" CC: Subj: RE: Help with SciAm article On Sat, 27 May 1995 JMB184@delphi.com wrote: > Thanks very much for your prompt and useful response. > I plan to do another search of my back issues, now > looking in the right place. Your recollection seems > adequate for my purposes. I had hoped the concept was > more practical, but at least now, I can put it to bed. > Thanks very much. > John Bailey > homepage--http://www.servtech.com/public/gcw/john/ Glad I could help. DId you know that the article also showed a Thai dance move which was based on this mechanism? Not hard to do. Hold your hand palm-up and place an object in it. Keeping it palm up, rotate it under your armpit and outwards as far as it will go, then raise your elbow high and over your head, and pass your hand back over your head, still keeping it (approximately) palm-up. Sweep it behind your head and down, and back to the starting position. You will have rotated the object without releasing it. If you do all this while moving your body in order to keep the object in a constant position, you will have duplicated the non-slipring workings mentioned in the article. Now, just do it with both hands at once with full wine glasses! .....................uuuu / oo \ uuuu........,............................. William Beaty voice:206-781-3320 bbs:206-789-0775 cserv:71241,3623 EE/Programmer/Science exhibit designer http://www.eskimo.com/~billb/ Seattle, WA 98117 billb@eskimo.com SCIENCE HOBBYIST web page Date: 27-MAY-1995 21:07:11.72 MAIL From: IN%"stuartf@sequent.com" "Stuart Friedberg" To: IN%"jmb184@delphi.com" CC: Subj: RE: Help with SciAm article In article you write: >Does anyone remember it? Have there been real world >applications of the technique? Yes. It is used in cable and rope winding machines. It is also a handy demonstration of group theory that most people don't believe until you demonstrate it in front of them. :-) Stu Friedberg (stuartf@sequent.com) ** End of message **