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Question

Asked by: Nate
Subject: Precession reversal
Question: What is your definition of Precession Reversal?
Date: 29 May 2014
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Answers (Ordered by Date)


Answer: Blaze - 29/05/2014 17:24:03
 Somehow I think there is more to this question than you are asking. The following is my definition and it may or may not match other people's definitions.

Precession is the 90 degree movement of a gyro that is a result of an applied input force. This means that changing the direction of the applied input force would change the direction of precession movement.

Precession reversal would be precession movement in the opposite direction which could be accomplished by spinning the flywheel in the opposite direction or by applying the input force in the opposite direction. Enough nutation can sometimes momentarily reverse precession movement.

regards,
Blaze



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Answer: Stan Smith - 29/05/2014 19:06:23
 A couple of points: gyroscopes do not precess at 90 degrees to the imposed couple; they only appear to do so. Movement at 90 degrees would contradict Newton's third law.
Gyroscopes can be made to precess in the opposite direction to that predicted by the normal rule.

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Answer: Blaze - 29/05/2014 20:09:10
 Ha, Ha. Very funny Stan. "they only appear to do so". Get a 100 pound gyro precessing at 10 feet per second and then stand in the way of it and let it hit you and see if it "only appear to do so".

By the way, Newton's first and second laws deals with motion. His third law deals with action/reaction.

From Wikipedia "Third law: When one body exerts a force on a second body, the second body simultaneously exerts a force equal in magnitude and opposite in direction on the first body." And that does happen when a gyro is precessing.

regards,
Blaze

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Answer: Stan Smith - 29/05/2014 20:51:44
 I am afraid that it is a fact. Gyroscopes undergo nutation as well as precession. It is a small effect, but nevertheless means that the overall movement complies with Newton's third law. Because it is small, nutation goes unobserved in 'crude' situations such as a top on a tower or a hand-held rotor.
The third law applies to all interactions, not just static ones. Newton also said that action and reaction were in the 'same right line'. There are apparent exceptions to that rule: charged particles for instance. But not gyroscopes. Nevertheless charged particles do obey the third law, contrary to what some textbooks claim.
Grandmothers. Eggs.

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Answer: Blaze - 29/05/2014 21:17:32
 Well regardless of whether "they only appear to do so" or actually do so, the resulting movement when a gyro is at "full precession speed" is at or very near to 90 degrees from the applied input force.

regards,
Blaze

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Answer: Glenn Hawkins - 30/05/2014 00:05:00
 Exactitude is like non-fiction. Sometimes fiction is truer. Perceptively, I know you know nothing can move in a straight line as you alluded to on another post. I think you must know to, the 90 degrees concept here is useful and truer than non-fiction as well, and really, I think it doesn't matter. Try something else. We are very interested. You were on a roll.

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Answer: Stan Smith - 30/05/2014 11:35:18
 It is the ninety-degree fallacy which led to the gyroscopic propulsion fallacy in the first place. Similarly, it is the schoolbook statement that Newton's laws do not apply in a rotating system (the force is radial, but the movement is tangential) which makes others try to use centrifugal force for propulsion. A less well-known fallacy is the one which claims that there is a delay between action and reaction even for objects in contact. Three scientists who held senior posts in the American aerospace and nuclear programs tried to exploit this nonsense in the 60s. Doesn't it make one feel safe that such incompetents were in positions of power during the Cold War?

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Answer: Ted Pittman - 30/05/2014 12:42:49
 Here's a video of Precession Reversal:
https://www.youtube.com/watch?v=0ubKR7_yS68


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Answer: Stan Smith - 30/05/2014 14:11:44
 That is not what I was referring to. It is possible to launch a simple top-on-tower set-up in such a way that the precession is opposite to what it says in textbooks (but not opposite to what it says in the wider academic gyroscopic literature).

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Answer: Ted Pittman - 30/05/2014 14:52:14
 Show it.

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Answer: Blaze - 01/06/2014 03:34:07
 Hi Glenn.

To me the question was about precession reversal, which I interpreted as after full precession speed is reached, not during the brief time it takes to get up to full precession speed.

Of all the people who write on this forum, I would venture a guess that I probably know the most about what happens during that brief time it takes to go from zero precession speed to full precession speed. That is because I have specifically studied it, experimented with it, filmed it and mathematically modeled it on different sized gyro systems. I can tell you with absolute confidence that when the input torque is applied to a gyro, the initial reacting movement is NOT at 90 degrees to the input torque, however in a very short period of time, when the gyro is at full precession speed, the residual movement is usually very, very close to 90 degrees to the input torque. So the net result is that (after a very brief period of time) a gyro precesses at 90 degrees to the applied input torque.

That is why I addressed the question the way I did, leaving out all of the complication that happens during the fraction of a second that a gyro is coming up to full precession speed.

cheers,
Blaze



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Answer: Glenn Hawkins - 01/06/2014 07:19:03
 Hi Blase,
This is very interesting and I had not seen it that way; certainly though it is true. Even while in the process of gaining study state, the precession reaction can be 89.999 more or less of a right angle, which is essentially the same as you say. Only now do I do I see that drop and precession degrade at the same changing degree and time. Very good.

My reply thought had not been to you, but to Stand though not naming him, suggesting that such minute differences as 89.999 : 90 was picking at straws, for as well as he knows nothing travels in a straight line, therefore a perfect angle, but when it is .001 different, why bother making a distinction. What I didn't know then was that he was studying particle acceleration so a billionth of a degree matters to him.

Cheers,
Glenn

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Answer: Glenn Hawkins - 01/06/2014 07:20:14
 Hi Blase,
This is very interesting and I had not seen it that way; certainly though it is true. Even while in the process of gaining study state, the precession reaction can be 89.999 more or less of a right angle, which is essentially the same as you say. Only now do I do I see that drop and precession degrade at the same changing degree and time. Very good.

My reply thought had not been to you, but to Stand though not naming him, suggesting that such minute differences as 89.999 : 90 was picking at straws, for as well as he knows nothing travels in a straight line, therefore a perfect angle, but when it is .001 different, why bother making a distinction. What I didn't know then was that he was studying particle acceleration so a billionth of a degree matters to him.

Cheers,
Glenn

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Answer: Ted Pittman - 11/06/2014 19:53:09
 Hello Blaze,
Thanks for your answer to my question. Would you elaborate more about "...the complication that happens during the fraction of a second that gyro is coming up to full precession speed..."?

Nate

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Answer: Blaze - 12/06/2014 00:57:10
 Hi Ted. Take a look at
http://www.gyroscopes.org/forum/questions.asp?id=1441

It is something that I wrote up just over 2 years ago and it is fairly accurate, although you might want to substitute the word "torque" for the word "force" in the posting. I have found through later experimentation and reviewing the movies of those experiments that the write up is generally correct. There is more happening during the fraction of a second the gyro is coming up to speed than is in the write up, but you can derive the rest from what is in the write up.

cheers,
Blaze


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