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I see. I understand what you're saying. The main thing I'm looking for in
this case, though, is a constant downward speed which does not accelerate.
Your ideas are interesting though, I will probably incorporate them into
future projects (a working Star Wars shuttle is a particularly neat idea,
I'd almost like to see pictures of yours).
--
Paul Davidson, aka Tinman
www.theforce.net | Your Daily Dose of Star Wars
www.filmforce.net | Your Daily Dose of Film News
Opens everywhere, January 2000
Peter Callaway <pcallaway@bmcl.com.au> wrote in message
news:FM1DuD.Box@lugnet.com...
> In lugnet.technic, Paul Davidson writes:
> > A counterweight doesn't change the speed at which something falls, does • it?
> > It may reduce the apparent weight of the main structure, but objects of
> > different weights fall equally fast.
>
> Not entirely true. Your thinking of the "what falls faster, a tonne of • lead or
> a tonne of feathers" question (or - "what's heavier, a tonne of lead or a
> tonne of feathers") which is actually more complicated than it seems.
>
> The thing with a counterwight is that it contains potential energy. From • what
> I understand you want to control the decent of an object. If you have a
> counterweight that is slightly lighter than the main object (ignoring
> mechanical loss in the pulley system, etc), gravity will take over the • descent
> of the object and it will gradually accelerate downwards (realising its
> potential, turning it into kinetic energy). Eventually it will reach a
> terminal velocity (I'm only ignoring mechanical loss, otherwise it will
> accelerate to infinity). Both the counterwight and the main object exert a
> downward force (acceleration x mass) on the system, but the net force is • down
> for the main object, and always increasing as acceleration has the per • second
> per second factor.
>
> In the wonderful world of reality you have mechanical losses due primarily • to
> friction in this case. There will be a point where the friction in the • system
> will balance out the net acceleration and the system will reach a constant
> velocity.
>
> With LEGO this will be difficult to achieve IMO as you are dealing with • small
> masses, which makes the system hard to fine-tune. A small difference in • the
> counterweight/main object weight will produce a slow decent, but it takes • a
> while to get going. The greater the weight difference the greater the • final
> velocity and the greater the acceleration. Inducing friction into the • pulley
> may help with the fine-tuning, either with elastic bands or using the • technic
> axle stoppers (the latter is a "cheap" way of doing it, but needs constant • re-
> adjusting as the stoppers work loose).
>
> I recently made a (very bad) Star Wars shuttle with moving wings. I used • the
> fly-wheel system to control the descent of the wings. Worked pretty well
> actually. I like the idea of the scissor system, perhaps combining it with • a
> pneumatic cylinder on the bottom arm to overcome the short cylinder travel • of
> the pneumatics, and as suggested crimp the outlet hose to control the • descent.
>
> I hope that makes sense. I guess I'm saying that all objects will • eventually
> fall at the same velocity (terminal velocity, and lets keep it to planet
> Earth's gravity), but there are ways and means to control the rate at • which
> this velocity is reached, and ways to control and reduce it. Hard to • explain
> in a short amount of time, and I hope I'm not teaching anyone to suck eggs • ;-)
>
>
> Pete Callaway
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