Subject:
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Re: Some help or advice requested
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Newsgroups:
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lugnet.technic
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Date:
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Fri, 22 Jan 2010 23:52:14 GMT
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Viewed:
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20537 times
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In lugnet.technic, Kevin L. Clague wrote:
> In lugnet.technic, Owen Dive wrote:
> > Hi all.
> >
> > I am currently working on a project (to be revealed in due course!) and I've
> > come across something of a stumbling block. I have a tray that is constrained to
> > move in one dimension, and a series of short liftarms under the tray, all
> > rotating in phase with each other, and placed such that once per rotation, they
> > connect with the tray (ok, so the tray can move vertically as well, but only a
> > little bit!) and move it along a specified distance. So far so good. What I need
> > is for the motor to change direction when the tray has reached the limit of its
> > travel, and to have such a mechanism at each end of the track, so the tray moves
> > back and forth for as long as power is supplied. Make sense?
>
>
> <snip>
>
> Hi Owen,
> As you say, you want a mechanism where the switch wants to be either on or
> off, but not in the middle. Had you thought about adding a pivot point at the
> top of the switch handle, with an axle going up and a weight at the top.
>
> Imagine the right hand switch, switched to the left, and the pivot having the
> weight directly above the pivot. The tray slides right, hits the axle, tipping
> the weight to the right. There is a limit on the pivot, so the weight's
> momentum then forces the switch to flip.
Hmm, an interesting solution.
> Presuming you can do that, then all
> you have to do is somehow get the weight back to the starting position.
But there's the rub! I'm afraid I can't see an obvious way to do that, given
that the weight will need to be positioned quite precisely. I will play around
with it, though, and see what I can come up with.
> This solution may not work, but it is worth a try. The word hysteresis comes
> to mind, but I'm not sure that is really the case here. I know the problem well
> though... Imagine a pneumatic piston flipping a pneumatic switch, but the
> switch's outputs control the piston. Once you hit the off position everything
> stops. Like you, I worked out a rubber band based mechanism where the switch
> hated to be off:
>
> http://www.kclague.net/oscillator/index.htm
>
> But given you already found one of my other "no off" solutions, you probably
> found this one as well.
I had indeed found that one, but was put off by "Once the piston achieves the
strength to move the handle, the pressure built up in the piston makes it snap
into motion. That snap gives the valve enough momentum to make it beyond the
center of travel on the switch.". I'm not working with pneumatics, so I don't
have the advantage of storing potential energy in that way. If I could figure
out a way to introduce some delay into the system, so that whatever pushes the
switch continues for a short while after the motor stops, then I'd be set!
Thanks for your input.
Owen.
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Message has 1 Reply:
 | | Re: Some help or advice requested
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| (...) <snip> (...) I've got a slightly different solution, where the tray tips an inverted pendulum right and left. The pendulum's momentum/weight flip the polarity reverser. The tri-blade bounds the inverted pendulum's swing. The first three steps (...) (14 years ago, 26-Jan-10, to lugnet.technic)
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Message is in Reply To:
| | Re: Some help or advice requested
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| (...) <snip> Hi Owen, As you say, you want a mechanism where the switch wants to be either on or off, but not in the middle. Had you thought about adding a pivot point at the top of the switch handle, with an axle going up and a weight at the top. (...) (14 years ago, 22-Jan-10, to lugnet.technic)
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