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In lugnet.org.ca.rtltoronto, Jeff Elliott writes:
> I think it'll take 40. I can loan you some if you need 'em.
40! Crap. I'll have to see what I've got when I get home.
> I'm not clear on the range of motion on the ride - I take it the head
> swings back and forth, hanging from the place where the 4 legs meet, but
> how far? Can it go right over the top? Or just 90 degrees each way?
You know, I think I've already stressed to Calum enough how tired I am of
hearing people in line, when they first join the queue, and they all turn to
one another and ask "Does it go all the way around?" :)
(Going all the way around isn't really viable and hasn't been done on rides
without counterweights, the acceleration you get without a counterweight is
devestating, results in something like 12 g near the bottom. It's why
roller coasters don't have circular loops*)
* - unless your name is Anton Schwarzkopf and you built "Thriller"**
** - "Thriller" by Schwarzkopf bent the rules by having two circular loops
right next to each other, unfortunatley it was shut down the day I visited
Astroworld in Texas to have a go on it...
But, as you discovered, the range of motion either way is a (very
impressive) 120 degrees.
> I'm tempted to try something with rubber bands... imagine two 6-hole
> pulley wheels facing each other like discs in a transmission. Now,
> attach bands between, say, 2, 3, 4, or 6 of the paired holes in the
> disc. Keep 'em loose. When the motor starts, it'll begin winding the
> elastics around one another, building up tension rapidly. When the
> tension becomes enough to move the ride, it'll start to swing, slowly at
> first, and gaining speed. Depending on the power of the motor, and
> gearing, and the bands, I'm betting you could get a nice pendulum swing
> by reversing the motor with the right period. The trick is to gear to
That makes a lot of sense, but unfortunatley that isn't my problem:
> Oh - one other problem you're going to run into: Period of a pendulum
> doesn't scale: If your model is, say, 100 times smaller, the period
> will be the square root of that, (10 times) faster. So if the Psyclone
> (<- see? I spelled it properly) gets a sedate swing of about 10 seconds
> (a simple, undriven 25m pendulum), your model would have an undriven
> period of, um, 1s. Eek. More akin to the spin cycle in a laundry
> machine...
This, itself, is the problem I was trying to get around by using a flywheel.
The only way in a scale model to get the pendulum to go slower really is to
put a counterweight on it, but since that is out of the question I am trying
to put a high-speed flywheel in line with the drive so that it is a "Forced"
swing, that is, it is not a pendulum for hte model anymore it is just a
driven arm, that is being driven by the acceleration and deceleration of the
flywheel.
It should, in theory, work, however since friction is naughty on things like
this I have a feeling even this won't work smoothly. And I dont know how to
do nice smooth sinusoidal accelerations of motors wiht NQC...
If I can't get past the drive head issue and geting it to swing smoothly
then I will not proceed any further with this, if I am going to build a
model of this then it has to run very smoothly and true to life.
And yeah, Revolution is so large that the period of swing is something in
the order of 10 seconds. It's really, really, really incredible to watch.
It seems to stay up in the air forever.
(I can't remember how to calculate swing - did you, and thats how you got 10
sec. for 25 m pendulum?)
Iain
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Message has 1 Reply:
 | | Re: Decagon?!
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| (...) Huh, good point, hadn't thought about the gmax at the bottom :) Mind you, 7 or 8 G sounds like fun... (...) I'd point out that circular motion and sinusoidal motion are interrelated... if you use a cam or off-centre gear drive, you could get (...) (22 years ago, 4-Sep-02, to lugnet.org.ca.rtltoronto)
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Message is in Reply To:
| | Re: Decagon?!
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| (...) Thanks, Iain. :) (...) I'm not. Lucky thing, my clothes wouldn't fit if I was Bjork. (...) Nope, it just became "Cyclone" in my head and I didn't go back to look at the name... (...) I think it'll take 40. I can loan you some if you need 'em. (...) (22 years ago, 4-Sep-02, to lugnet.org.ca.rtltoronto)
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