Question |
| Asked by: |
Blaze |
| Subject: |
Does the flywheel rpm have to increase with increased precession speed? |
| Question: |
If one was to apply several G's to a gyro system (like if it were on a much larger planet), the precession speed would also increase. That is known.
The question is this: would the flywheel rpm have to be increased to prevent Newtonian effects during precession in the higher G environment? |
| Date: |
11 October 2012
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Answers (Ordered by Date)
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| Answer: |
Momentus - 11/10/2012 13:37:54
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| | Hi Blaze
Increasing the gyro torque (by any means) increases the precession speed.
A precessing gyro rotates about two axes and the vector sum of precession and spin is the original spin speed.
So to answer your question, the spin speed reduces as the precession increases this also conserves energy, an important check.
Try hanging the gyro from a bungee cord. Its good fun watching the precession speed changing, but to detect the associated changes in spin speed would require a sensitive tachometer.
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Blaze - 12/10/2012 02:58:27
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| | Thank you for your response Momentus.
I didn't think it was possible to actually change the rpm of the flywheel by changing other parameters in the system. I thought the only way to change the rpm of the flywheel would be to speed it up or slow it down with a motor. Certainly, if you slow down the flywheel (this usually happens naturally due to friction), the precession speed does increase and if you increase the flywheel speed the precession speed decreases but that is because all other system parameters remain constant (length of arm, gyro torque due to gravity, etc).
My theory, and I am just "spit balling" here, is that the flywheel simply acts as a "mechanical catalyst" to change gyro torque from gravity into precession and like any catalyst in a chemical reaction, it takes part in the reaction but does not get consumed by it. In other words the flywheel rpm does not change.
We know that if the flywheel rpm is too slow, Newtonian effects start happening. I believe that this is due to the flywheel not being able to fully convert the gyro torque into precession.
For example, if you have a constant flywheel speed of say 2000 rpm for a given gyro system and you wildly increase the gyro torque or the arm length so that the precession takes 1/100 of the time, then I would think that you would have to increase the flywheel rpm to prevent the Newtonian effects from coming into play at the higher precession speed because the ratio of flywheel rpm to precession rate is drastically different at the elevated precession speed.
Or am I imagining it wrong?
Blaze
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Momentus - 12/10/2012 12:50:08
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| | Blaze
The angular momentum of the gyroscope is fully and completely described in standard text books. There is no mystery, no need for a catalyst etc.
The mystery is that academics do not accept that by using the standard gyroscope formulae it can be demonstrated that Angular Momentum is not conserved.
If you look at this post :-http://www.gyroscopes.org/forum/questions.asp?id=460, 04/09/2005
I dealt with the changes to spin with high rates of precession, up to the point where the precession axis becomes the spin axis.
You are correct to say that torque applied to the axle of a flywheel does work, changes the speed. Torque applied at right angles to spin does no work, as there is no displacement at the point of applied force (the definition of work), as you well know, the displacement is orthogonal to torque, known as precession.
The loss of speed on one axis is equalled by the increase in speed on the other, orthogonal axis. As “The square of the hypotenuse of a right angled triangle , is equal to the sum of the squares of the two adjacent sides”, and energy is a square law, then the vector sum of the two rotations must equal the original spin speed. Unless you want to repeal the law of energy conservation.
Regardless of the speed of flywheel rotation, a gyroscope is orthogonal spin torque and precession.
Nitro has been posting lately and he has a wonderful expression which goes something like “It does not matter what you think you are doing, the gyroscope is precessing torque”
I hope this aids your understanding.
Keep posting
Momentus
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Blaze - 14/10/2012 00:45:13
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| | Yes, of course what you say makes sense Momentus, but that is not really what I am asking about.
What I want to know is does the flywheel have to have a higher rpm for a faster precession rate to prevent Newtonian effects? After reading your answers, I realized that I have already done this experiment and know the answer.
I have a 2 pound, 5 inch diameter flywheel spun up to 1750 rpm. When precessing with a 2.25 inch arm there are no Newtonian effects. With the same 1750 rpm and a 3.5 or 4 inch are there are large Newtonian effects. I had to increase the flywheel to about 2200 rpm for the 3.5 inch arm to prevent Newtonian effects when precessing. So, for a faster precession rate, the flywheel rpm has to be greater to prevent Newtonian effects. That is what I wanted to know, however I did learn something from your answer too.
Blaze
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Glenn Hawkins - 14/10/2012 23:39:54
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| | Hello Blaze,
I was happy to see you again. Yes, yes you have the answer. Years ago I would spin up a gyro, put it to precessing around a tower and hit the 'free' knob circling straight down with a 20oz. framing hammer. The gyro would fly ten or twelve feet off the table in one direction, while the tower flue fast into a wall in the opposite direction. I took that to mean pretty much what you are saying it means.
Glenn,
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Blaze - 15/10/2012 00:19:58
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| | Thanks Glenn. I wouldn't have asked the question if I had realized that I already had the answer. The experiment I was doing was to try to prove something else entirely, that is why I didn't think about the flywheel rpm versus precession rate thing. It just so happened that the experiment answered my question about that too.
So, the followup question is this:
If the flywheel rpm was just sufficient to prevent Newtonian effects and you double the gyro torque, would you also have to double the flywheel rpm to prevent Newtonian effects at the higher precession rate? I am thinking it may not be linear relationship so the rpm would have to increase but probably not double.
Your thoughts on the followup questions?
Blaze
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Glenn Hawkins - 15/10/2012 13:08:59
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| | Good morning Blaze,
It is good to converse again. I have believed for a long time that the Newtonian effects never go away, but are merely overwhelmed. Yes to your general question about doubling both forces to prevent Newtonian effects -- I am certain. I am not sure of the ratios, but double would be my guess. Great idea it was to question the linear relationship. We could think about that and talk. The idea has come to mind many times, because it is important. I think this way.
The liner effects are determined by the speed of precession, which is built by the ratio between angular momentum to toque. Those two; angular momentum and torque seem to be a constant, not a variable in maintaining same precession speed. You can maintain the same precession speed by keeping spin and torque in equilibrium, regardless of the magnitude of forces applied. God! I hope that is not true, but it would seem to be.
You are really asking the right questions. I have always wondered if by applying greater, shall we say dual forces, could there be some variation between the two that would allow an increase precession speed-- WITH OUT increasing the Newtonian effect. I think you understand the implication and that is why you seek an answer to this question. I hope you can add more reason for us.
Glenn,
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Blaze - 15/10/2012 18:23:22
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| | Well, lets assume that for a given gyro system, the gyro precesses once every 3 seconds, the flywheel rpm is 2000 and that this is JUST enough for this gyro system to NOT display any Newtonian effects. That means for this system, if you were to speed up the precession any amount without changing any other parameters you would get Newtonian effects.
Now, using the standard precession calculation, if you were to double the gyro torque (down force) or you were to double the arm length, it would double the precession to once every 1.5 seconds. However if you were to also speed up the flywheel rpm to 4000 at the same time as you doubled the gyro torque or doubled the arm length, you would end up with a system that precesses once every 3 seconds, just like before you made any changes.
I would say that the second scenario would likely not display any Newtonian effects either because the precession rate is also once every 3 seconds which, for this hypothetical case, was just slow enough NOT to display any Newtonian effects.
So does that mean that for a given gyro system there is a maximum precession speed that it can operate without displaying any Newtonian effects?
Blaze
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Glenn Hawkins - 15/10/2012 19:24:18
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| | Blaze: "So does that mean that for a given gyro system there is a maximum precession speed that it can operate without displaying any Newtonian effects?"
Sadly that would seem to be true. Remember that I said: "God I hope that is not true.”
You can however change the system! by lengthening the arm and increasing spin speed. The thing should then precess at the same RPMs, but of course, due to the greater circumference, the speed of the traveling gyro should be greater and impact correspondingly greater. It is because you add more torque to the system, that precession should respond unlike rotation, the ice scatter you know. Instead it is the reverse. The outer may travel actually faster than the inter.
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Blaze - 17/10/2012 01:04:50
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| | Glenn: I have believed for a long time that the Newtonian effects never go away, but are merely overwhelmed.
Bingo Glenn. I think you got it. The Newtonian effects SHOULD always be there in diminishing amounts as you precess slower and slower. It is just that you don't always see them for the slower precession rates because the pivot friction against whatever the pivot is resting on is great enough to prevent the pivot from moving about.
This could also explain why a gyro hung from a string makes the string cone. That coning would be the small amount of Newtonian effect that actually shows up because it is greater than the pivot friction which is extremely small because the pivot is a long string.
The only way to prevent any Newtonian effects would be to have the flywheel spinning at a theoretical infinite speed which would mean the precession rate would theoretically be zero.
Your thoughts?
Blaze
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Glenn Hawkins - 19/10/2012 22:00:19
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| | Blaze, You are right. The frictions form the force downward on the pivot remains essentially the same regardless of precession speed. Centrifuge you knew weakens with slowed precession speed. You have it. I have noted that by extending the arm precession is faster and will pull the gyro off the pedestal toward the horizontal. You've increased centrifuge, with out increasing pivotal friction.
The mesmerizing condition is as Sandy Kidd discovered. When you force precession to circle the pivot faster and faster centrifuge although greater, is nevertheless overcome by corresponding greater and greater freak-like centripetal effects, which causes the wheel to want to travel inward toward the hub.
There is connection that could allow an inward pull. It is an outer push toward the pivot and just the opposite of centrifuge to counter it.
This is due to a poorly named 'deflection condition' that causes the gyro to act so strangely. I cannot imagine infinite.
The cone, sometimes it is large, sometimes small it seems regardless of observable factors. I am sure I am missing something. Maybe you can discover it.
Regards Glenn,
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Glenn Hawkins - 23/10/2012 18:54:18
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| | Correction to the word 'LEFT OUT' in the above post.
There is 'NO' connection that could allow an inward pull. It is an outer push 'INWARD' toward the pivot and just the opposite of centrifuge. This counters the Newtonian centrifugal effect.
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Blaze - 25/10/2012 01:00:04
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| | Glenn: "It is an outer push 'INWARD' toward the pivot and just the opposite of centrifuge. This counters the Newtonian centrifugal effect."
There is no inward push as I see it. It is simply precession that is moving the flywheel inward towards the pivot.
Blaze
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Glenn Hawkins - 25/10/2012 01:34:03
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| | Exactly. The statements say the same thing. The inward push is in fact the deflection, push, or movement as you prefer.
The push is created in thin air so to speak. It is the invisible action of the wheel being literally bounced/vibrated/deflected toward the pivot. Centripetal contrary to deflections has an actual connection between the pivot and rotating object such as with a string, or chain. It is said that the string pulls the object in a circular path. We can see that. You knew this. Thank you for replying and thank you for an honest evaluation.
Have a good evening my friend,
Glenn
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Blaze - 27/10/2012 01:46:19
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| | Again, this is as I see it. The precession "force" causing the flywheel to rise is greater than the centrifuge force that is trying to prevent the flywheel from rising, so the flywheel rises. If the centrifuge force were greater than the precession force the flywheel would not rise. So for a flywheel spinning at very low rpm it would take a lot higher hub rotation rpm to cause the flywheel to rise than if the flywheel were spinning at a high rpm. One could probably calculate where the cross over point would be for any flywheel rpm vs hub rotation.
This is the same as a gravity powered system where the precession is hurried along with your finger. The flywheel rises because it is precessing upwards due to the force supplied by your finger. In this case there is centrifugal force as well that is being overcome.
Just my thoughts on the matter.
That being said, I believe that there is little if any centrifugal or centripital forces acting on a steady state precessing gyro. There is a completely different set of actions or motions that keep the axle on the pivot, but that is just my theory. Some of this was actually proved in the treehouse experiment that I did a while back but that is food for another thread.
best to all,
Blaze
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Glenn Hawkins - 27/10/2012 22:39:12
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| | But I have not mentioned ‘rise’. I speak only of horizontal positions and horizontally opposing forces, the inward/outward forces. The word precession does not explain precession, but the word deflection does. What is being confused is the nature of deflections. Deflections are only a part of precession. I see them as pacifically separate things that work in conjunction with one another and rely on one another. When we wonder why precession is, deflections are the why and how of the explanation of it. That is ‘how it works’ If I were to go on, I would try again to explain deflects, although admittedly the word is a poor descriptive choice. I tried several times before on the site.
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