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Question: If you have one of those gizmos that transforms rotational
motion to reciprocating motion, what path does the reciprocating part trace?
Answer: As far as I can tell, the path is
cos a + Sqrt(k^2 - sin^2 a)
where k is the length of the connecting rod that is free to pivot. As
you can see, that means that for large k, the path is approximately a
sine wave. However, for small k it deviates significantly from a simple
sine wave...
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Le 28/09/2010 10:09, Invisible a écrit :
> Question: If you have one of those gizmos that transforms rotational
> motion to reciprocating motion, what path does the reciprocating part
> trace?
>
> Answer: As far as I can tell, the path is
>
> cos a + Sqrt(k^2 - sin^2 a)
>
> where k is the length of the connecting rod that is free to pivot. As
> you can see, that means that for large k, the path is approximately a
> sine wave. However, for small k it deviates significantly from a simple
> sine wave...
You are also forgetting in the equation the offset between the axes
(when the center of rotation is not aligned with the translation path).
--
A: Because it messes up the order in which people normally read text.<br/>
Q: Why is it such a bad thing?<br/>
A: Top-posting.<br/>
Q: What is the most annoying thing on usenet and in e-mail?
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On 28/09/2010 09:14 AM, Le_Forgeron wrote:
> You are also forgetting in the equation the offset between the axes
> (when the center of rotation is not aligned with the translation path).
If the center of rotation isn't aligned with the translation path, would
the device even *work* any more? Certainly I've never seen that done
(and hence it doesn't interest me).
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Le 28/09/2010 10:25, Invisible a écrit :
> On 28/09/2010 09:14 AM, Le_Forgeron wrote:
>
>> You are also forgetting in the equation the offset between the axes
>> (when the center of rotation is not aligned with the translation path).
>
> If the center of rotation isn't aligned with the translation path, would
> the device even *work* any more? Certainly I've never seen that done
> (and hence it doesn't interest me).
If the "engine" is the wheel, it always works.
If the "engine" is the translation, it works also, but an inertial wheel
is recommended. (used with 8 mm offset on 450 Honda engine)
If you want a true sine movement (for a constant rotational speed), you
need a scotch yoke system.
http://demonstrations.wolfram.com/ComparingSimpleCrankSliderAndScotchYokeMechanisms/
http://demonstrations.wolfram.com/SliderAndCrankMechanism/
--
A: Because it messes up the order in which people normally read text.<br/>
Q: Why is it such a bad thing?<br/>
A: Top-posting.<br/>
Q: What is the most annoying thing on usenet and in e-mail?
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On 28/09/2010 11:14 AM, Le_Forgeron wrote:
> If you want a true sine movement (for a constant rotational speed), you
> need a scotch yoke system.
This is what I was really interested to find out - how much the motion
of a simple crank deviates from a pure sine wave. Apparently the answer
is "it varies, depending on the length of the crank".
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