Inertia Machine
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waspy,
I have to admit, your description leaves me breathless ("...simulation (stepping at 0.001s) where the torque is constant at 1 positive 0-π and negative π-2π.")
What the heck are you saying? That you rotationally accelerate the mass in one direction, and decelerate it in another, yet produce a force?
I have to admit, your description leaves me breathless ("...simulation (stepping at 0.001s) where the torque is constant at 1 positive 0-π and negative π-2π.")
What the heck are you saying? That you rotationally accelerate the mass in one direction, and decelerate it in another, yet produce a force?
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Nick, I liked your rocket in a bag as it somes up the situation nicely.
I modelled purely the behaviour that Jiff described. The net result is that a force acts (or more importantly must be reacted). If you visualise how such a motion can be produced then the situation becomes clearer.
Imagine a two stroke engine (running with just enough fuel to overcome friction). On the power stroke a force is generated and accelerates the crankshaft (0° - 180°), it then goes into compression decelerating the crankshaft (180° - 0°). If you look at the forces on the piston (assuming 0° is at the top of the stroke) the power stroke exerts a downward force created by the expanding gases, and the compression stroke exerts a downward force on the piston by the gases resisting compression.
Now look at only the crankshaft's motion (no piston or connecting rods) without assuming how it is created. You see a rotating mass that accelerates around half its cycle and decelerates around half its cycle, this matches the description that Jiff has presented to us.
In the piston engine the torque is created via the piston, and reacted via the piston. In Jiff's machine the torque is created at the driveshaft, momentum is changing and therefore a force must be acting. Unfortunately there Jiff's description ends. Jiff has put a bag around only half of his machine.
I am not aware of any means of creating the torque, as described by Jiff, without the reactive torque (and therefore a similar force) acting on the body of the machine. However my ignorance doesn't mean it isn't possible.
I think we agree as to the impracticality of Jiff's machine, but I still maintain that the original description does what it says.
I modelled purely the behaviour that Jiff described. The net result is that a force acts (or more importantly must be reacted). If you visualise how such a motion can be produced then the situation becomes clearer.
Imagine a two stroke engine (running with just enough fuel to overcome friction). On the power stroke a force is generated and accelerates the crankshaft (0° - 180°), it then goes into compression decelerating the crankshaft (180° - 0°). If you look at the forces on the piston (assuming 0° is at the top of the stroke) the power stroke exerts a downward force created by the expanding gases, and the compression stroke exerts a downward force on the piston by the gases resisting compression.
Now look at only the crankshaft's motion (no piston or connecting rods) without assuming how it is created. You see a rotating mass that accelerates around half its cycle and decelerates around half its cycle, this matches the description that Jiff has presented to us.
In the piston engine the torque is created via the piston, and reacted via the piston. In Jiff's machine the torque is created at the driveshaft, momentum is changing and therefore a force must be acting. Unfortunately there Jiff's description ends. Jiff has put a bag around only half of his machine.
I am not aware of any means of creating the torque, as described by Jiff, without the reactive torque (and therefore a similar force) acting on the body of the machine. However my ignorance doesn't mean it isn't possible.
I think we agree as to the impracticality of Jiff's machine, but I still maintain that the original description does what it says.
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That's it, strictly speaking it's half a machine.
It is not unlike drawing a rotor head without anything at the other end of the driveshaft. Eventually you face the fact that somehow you have to counter the torque.
It is not unlike drawing a rotor head without anything at the other end of the driveshaft. Eventually you face the fact that somehow you have to counter the torque.
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Waspy, i imagine Jiff's machine driven by a turboshaft driving a mechanism to vary the rotational speed - it's primary intent is afterall a VTOL craft. Your analysis (Excel, Delphi or Fortran i presume) cannot have included the centrifugal force (Mass*Radius*(Rad/Sec)^2) acting along the radius. If it had you would see that increasing the rotational speed would negate the force in the Pi azimuthal direction over a complete cycle period. The machine will just sit there shaking, but absolutely nothing more.
For this sort of problem keep the analysis simple. In this case it can be reduced to the fact that there is no means to provide reaction. End of story.
For this sort of problem keep the analysis simple. In this case it can be reduced to the fact that there is no means to provide reaction. End of story.
Last edited by Graviman; 19th Jul 2007 at 08:46.
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I feel this technology would work well for STOL and VTOL applications however there are many other applications.
With regard to the analysis lets remember that there are analytical packages that will tell you that it is OK to balance a 1,000,000 ton weight on a mm diameter wire that is a mile long. Before you continue your passionate affair with your package of choice remember to keep one eye above the monitor.
Have we considered an angular X,Y force plot?
Regards
Jiff
With regard to the analysis lets remember that there are analytical packages that will tell you that it is OK to balance a 1,000,000 ton weight on a mm diameter wire that is a mile long. Before you continue your passionate affair with your package of choice remember to keep one eye above the monitor.
Have we considered an angular X,Y force plot?
Regards
Jiff
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My simulation is Excel for case 1 of constant torque,
and a toolset I created in F90 many years ago for case 2 of proportional torque. This was due to a need to carry out a convergent iteration for position.
I modelled a point mass in free space with the forces necessary to create the motion described in a rotating frame of reference,
I chose to use centripetal force ~v2,
and normal to that, tangential which depends on the case.
For case 1 it was constant but swapping sign at the top of the circle. (assumption)
For case 2 ~θ similar to SHM. (assumption)
I am aware of no other forces acting on the mass to create the described motion.
The tangential force, created by the torque, causes an increase in angular velocity.
The centripetal force, necessary to maintain circular motion, grows from minimum at the bottom to maximum at the top as the mass reaches its maximum angular velocity, and then reduces back to mimimum at the bottom.
Draw out all the "centrifugal forces" acting on the mass as it travels around its circular path if you wish. Or consider that if the torque magnitude is symmetrical laterally (assumption), then all the centrifugal forces in the bottom half of the circle are always smaller then their mirror in the top half, as the velocity is always greater in the top half of the cricle than the bottom. Due to the reversal of the torque, the tangential force always has a vector horizontal or above.
Graviman, with your engineering experience, can you please point to the incorrect assumption(s) or the ommission(s) in the above analysis that lead to your statement that my analysis is "garbage". I am always willing to learn from my mistakes.
In mechanical implementation. The torque acts at the driveshaft, is transferred via the rotor arm, creating acceleration. The centripetal force is provided by the rotor arm, constraining the motion to a circular path. This force must be reacted at the driveshaft end. The changing centrifugal force (in reality the reaction of the centripetal) doesn't negate anything, but in fact is the mechanism for the linear force creation.
I suggest a turboshaft is a bit of overkill, and not the best way to create varying rotational motion. I imagine that Jiff is thinking some form of electrical motor to create the torque, with polarity changing to produce the reversal. This is all assumed implementation of course.
Jiff, creating the torque is just one (and probably the least) of your problems.
1. How do you react the opposing torque on the engine body, such that it doesn't undergo an equal and opposite motion? If not reacted this would produce an equal and opposite motion. Net change at best is rotation.
2. Instinctively I suspect that the centre of mass of the rotor is towards the lump at the end. The motion would therefore be both mass and drive mechanism rotating about this centre and causing an almost self cancelling effect. How do you intend to "anchor" the driveshaft?
3. When the body starts to translate, the motion is no longer circular, and the torque would have to be varied in order to maintain the same equations of motion, as the start and end point are no longer the same place. How do you intend to calculate and compensate for this effect?
and a toolset I created in F90 many years ago for case 2 of proportional torque. This was due to a need to carry out a convergent iteration for position.
I modelled a point mass in free space with the forces necessary to create the motion described in a rotating frame of reference,
I chose to use centripetal force ~v2,
and normal to that, tangential which depends on the case.
For case 1 it was constant but swapping sign at the top of the circle. (assumption)
For case 2 ~θ similar to SHM. (assumption)
I am aware of no other forces acting on the mass to create the described motion.
The tangential force, created by the torque, causes an increase in angular velocity.
The centripetal force, necessary to maintain circular motion, grows from minimum at the bottom to maximum at the top as the mass reaches its maximum angular velocity, and then reduces back to mimimum at the bottom.
Draw out all the "centrifugal forces" acting on the mass as it travels around its circular path if you wish. Or consider that if the torque magnitude is symmetrical laterally (assumption), then all the centrifugal forces in the bottom half of the circle are always smaller then their mirror in the top half, as the velocity is always greater in the top half of the cricle than the bottom. Due to the reversal of the torque, the tangential force always has a vector horizontal or above.
Graviman, with your engineering experience, can you please point to the incorrect assumption(s) or the ommission(s) in the above analysis that lead to your statement that my analysis is "garbage". I am always willing to learn from my mistakes.
In mechanical implementation. The torque acts at the driveshaft, is transferred via the rotor arm, creating acceleration. The centripetal force is provided by the rotor arm, constraining the motion to a circular path. This force must be reacted at the driveshaft end. The changing centrifugal force (in reality the reaction of the centripetal) doesn't negate anything, but in fact is the mechanism for the linear force creation.
I suggest a turboshaft is a bit of overkill, and not the best way to create varying rotational motion. I imagine that Jiff is thinking some form of electrical motor to create the torque, with polarity changing to produce the reversal. This is all assumed implementation of course.
Jiff, creating the torque is just one (and probably the least) of your problems.
1. How do you react the opposing torque on the engine body, such that it doesn't undergo an equal and opposite motion? If not reacted this would produce an equal and opposite motion. Net change at best is rotation.
2. Instinctively I suspect that the centre of mass of the rotor is towards the lump at the end. The motion would therefore be both mass and drive mechanism rotating about this centre and causing an almost self cancelling effect. How do you intend to "anchor" the driveshaft?
3. When the body starts to translate, the motion is no longer circular, and the torque would have to be varied in order to maintain the same equations of motion, as the start and end point are no longer the same place. How do you intend to calculate and compensate for this effect?
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Waspy, we are just going to have to agree to disagree. I am convinced your analysis is wrong, but genuinely have no time to discuss the details (big project & second degree in physics). I can only refer you to some info about circular motion, for you to check your vector sums:
http://en.wikipedia.org/wiki/Circular_motion
To me it is very simple, nothing is being reacted against. If mech worked you require no energy to keep the weights rotating, but somehow produce kinetic energy in your craft. This is just plain wrong, so i stand by my assertion that the analysis has produced a garbage result.
http://en.wikipedia.org/wiki/Circular_motion
To me it is very simple, nothing is being reacted against. If mech worked you require no energy to keep the weights rotating, but somehow produce kinetic energy in your craft. This is just plain wrong, so i stand by my assertion that the analysis has produced a garbage result.
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I understand circular motion.
I understand Keppler's laws of planetary motion that indicate that as the Cp force changes (due to varying radius of rotation) the tangential vleocity changes, such that the area swept out remains constant, i.e. a change in velocity indicates a change in force.
Visualisation of this is counterintuitive, but it helps of you imagine how to create the motion (try attached to a sealed piston of gas) If you ignore friction etc. once started the system continues without additional energy, and the linear force is seen on the piston.
If the system starts to translate through space, then the work done on one side is greater than that on the other. An effect not identical, but similar to the advancing vs retreating blade on a helicopter. Hence where the energy transfer occurs.
Good luck with the 2nd degree.
I understand Keppler's laws of planetary motion that indicate that as the Cp force changes (due to varying radius of rotation) the tangential vleocity changes, such that the area swept out remains constant, i.e. a change in velocity indicates a change in force.
Visualisation of this is counterintuitive, but it helps of you imagine how to create the motion (try attached to a sealed piston of gas) If you ignore friction etc. once started the system continues without additional energy, and the linear force is seen on the piston.
If the system starts to translate through space, then the work done on one side is greater than that on the other. An effect not identical, but similar to the advancing vs retreating blade on a helicopter. Hence where the energy transfer occurs.
Good luck with the 2nd degree.
Avoid imitations
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I like the concept. I think the latest development means that if I remove the balance shaft from the engine of my motorcycle it will fly, Yippee!
I always wondered why they fitted them, I previously thought it was just to reduce horizontal vibrations caused by the vertical balancing of the crankshaft assembly.
Now, where's my socket set?
I always wondered why they fitted them, I previously thought it was just to reduce horizontal vibrations caused by the vertical balancing of the crankshaft assembly.
Now, where's my socket set?
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waspy,
Your explanation is now finally clear, and also completely wrong.
Like the downwind turn, the concept of the machine inventing a force as it is being "swept through space" is a mis-reading of what an "inertial reference frame" is.
Please go back and look again at how Galileo and Newton defined the reference frames for their laws. A translating frame does NOT change the relationship. Otherwise our 33,000 mph trip around the sun would make a big difference in your tire wear as you turned certain corners!
Your analysis, and Jiff's device, are a lot of hooey. I think I will end my attempts to teach Physics 101 to the both of you.
Shytorque, remove that balance arm and hit them with it, please!
Your explanation is now finally clear, and also completely wrong.
Like the downwind turn, the concept of the machine inventing a force as it is being "swept through space" is a mis-reading of what an "inertial reference frame" is.
Please go back and look again at how Galileo and Newton defined the reference frames for their laws. A translating frame does NOT change the relationship. Otherwise our 33,000 mph trip around the sun would make a big difference in your tire wear as you turned certain corners!
Your analysis, and Jiff's device, are a lot of hooey. I think I will end my attempts to teach Physics 101 to the both of you.
Shytorque, remove that balance arm and hit them with it, please!
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Hehehe, i was going to comment about keeping an eye out for loose screws under the machine. I like this response better!
http://en.wikipedia.org/wiki/Inertial_frame
Waspy, a lot of folks here think you have some fundamental misunderstanding. In my experience a good grasp of the fundamentals gives good intuition about these sorts of concepts. Mine tells me that it just will not work...
http://en.wikipedia.org/wiki/Inertial_frame
Waspy, a lot of folks here think you have some fundamental misunderstanding. In my experience a good grasp of the fundamentals gives good intuition about these sorts of concepts. Mine tells me that it just will not work...
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Back in your boxes gentlemen. I have said many times that we only have half the mechanism drawn, not only that but it is drawn for the static case (i.e. the situation changes once moving).
Shy,
In your engine all the forces can be held in balance by the fact that opposite to the piston force is a force acting on the cylinder head. By the way, why do you need any form of balancing if a rotating mass can't create lateral force at any particular instant in time?
Nick,
I responded to Graviman's intuition that says that Kinetic Energy appears to be created from nowhere. Quite rightly Graviman has looked at the machine and sees that no energy can get transferred as everything is symmetrical. Yet apparently the kinetic energy of the body increases (to a stationary observer). What I have attempted to illustrate by analogy is that the asymmetry is created by the movement (change in velocity) of the body itself. I suggest that you yourself go back and consider your application of frames of reference, they must be of constant velocity in order to be inertial. If the body is in constant velocity then there is no change in KE.
Graviman,
But nobody can actually tell me what it is. They can make belittlling comments, they can talk about intuition, but they can't show me where I have applied incorrect physics, or made an assumption or ommission. That's all I'm asking for, is a technical answer to a technical problem.
I will state my fundamental intuition simply.
If a rotating mass cannot create a lateral force, why do we bother worrying about vibration?
If a rotating mass can create a lateral force, then if we can vary the rotation, then we can vary the force. If we can vary the force cyclically, we create a net force.
I also maintain that the impracticality is not in what Jiff has drawn, but in the creation of the torque, and the managing of the reaction of the forces through the point that creates the torque.
Shy,
In your engine all the forces can be held in balance by the fact that opposite to the piston force is a force acting on the cylinder head. By the way, why do you need any form of balancing if a rotating mass can't create lateral force at any particular instant in time?
Nick,
I responded to Graviman's intuition that says that Kinetic Energy appears to be created from nowhere. Quite rightly Graviman has looked at the machine and sees that no energy can get transferred as everything is symmetrical. Yet apparently the kinetic energy of the body increases (to a stationary observer). What I have attempted to illustrate by analogy is that the asymmetry is created by the movement (change in velocity) of the body itself. I suggest that you yourself go back and consider your application of frames of reference, they must be of constant velocity in order to be inertial. If the body is in constant velocity then there is no change in KE.
Graviman,
Waspy, a lot of folks here think you have some fundamental misunderstanding.
I will state my fundamental intuition simply.
If a rotating mass cannot create a lateral force, why do we bother worrying about vibration?
If a rotating mass can create a lateral force, then if we can vary the rotation, then we can vary the force. If we can vary the force cyclically, we create a net force.
I also maintain that the impracticality is not in what Jiff has drawn, but in the creation of the torque, and the managing of the reaction of the forces through the point that creates the torque.
Avoid imitations
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Shy,
In your engine all the forces can be held in balance by the fact that opposite to the piston force is a force acting on the cylinder head. By the way, why do you need any form of balancing if a rotating mass can't create lateral force at any particular instant in time?
In your engine all the forces can be held in balance by the fact that opposite to the piston force is a force acting on the cylinder head. By the way, why do you need any form of balancing if a rotating mass can't create lateral force at any particular instant in time?
.On a plain crankshaft the mass of the pistons and con-rods would cause severe out of balance rotational forces / vibration. The crankshaft is therefore shaped/forged with balance weights to counterbalance their mass - if this wasn't done the engine would shake itself to bits.
Unfortunately, the crankshaft balance weights also go through the lateral "fore and aft" positions during their 360 degree rotation and in those positions they themselves are not opposed by the up/down movement of the pistons and con-rods. This results in fore and aft vibration. For this reason, engine designers traditionally never fully balanced a crankshaft; they "left off" some balance mass as a compromise between allowing vertical and longitudinal vibrations.
This was very obvious on single cylinder or twin cylinder motorcycles up until the 1970s, where the engine was often bolted rigidly in the frame and the rider felt those out of balance forces through his most sensitive regions.
The BSA Goldstar (500 single) was a "classic" example. At idle, the bike can be seen to rock fore and aft on it's wheels as the crankshaft mass balance goes through the fore and aft positions.
These days engines are much more sophisticated and multi cylinders prevail but as far as I am aware, the basic rules of physics have never changed.
In modern engines, a balance shaft is sometimes fitted to oppose some of the lateral vibrational forces. My Honda four cylinder motorcycle has one, unless their designers and salesman have been conning me
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Newtonian Physics 101
Waspy, this is what bothers me: You demonstrate a fundamental misunderstanding about simple engine balancing, then proceed to try to tell us that not only should we disregard linear momentum but that physics has been wrong for years about conservation of energy. Much to my annoyance i am no longer involved in engine design/simulation/development, but if project delivery was at stake i would beat a path to well understood principles of mechanics - every time.
http://ocw.mit.edu/OcwWeb/Physics/8-...ures/index.htm
This Walter Lewin lecture series on mechanics is well worth watching - if only for the great entertainment value. Please review these, since it will help you gain the grounding you need to discuss such concepts.
http://ocw.mit.edu/OcwWeb/Physics/8-...ures/index.htm
This Walter Lewin lecture series on mechanics is well worth watching - if only for the great entertainment value. Please review these, since it will help you gain the grounding you need to discuss such concepts.
Last edited by Graviman; 17th Jul 2007 at 16:51.
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Waspy,
I mean vibrational forces, the important point being that they occur in one direction, then the other at the same amplitude.
Again if not, as I joked earlier, my bike would fly (or sink into the earth if I was unlucky).
I mean vibrational forces, the important point being that they occur in one direction, then the other at the same amplitude.
Again if not, as I joked earlier, my bike would fly (or sink into the earth if I was unlucky).
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Please go back and look again at how Galileo and Newton defined the reference frames for their laws. A translating frame does NOT change the relationship. Otherwise our 33,000 mph trip around the sun would make a big difference in your tire wear as you turned certain corners!
You demonstrate a fundamental misunderstanding about simple engine balancing
then proceed to try to tell us that not only should we disregard linear momentum but that physics has been wrong for years about conservation of energy
I have tried to identify the bit of Jiff's machine that appears impossible. It proved difficult firstly because it is not drawn, it is part of the assumptions.
The static case works perfectly, but then again there can be assumed to be a reaction force at the driveshaft, keeping everyone happy. Once it is free to translate then the generation of torque, also implies a generation of reaction force. If not the circular motion becomes highly erratic.
I've said before, we are seeing half of a complete engine. If you analyse a rotor head and blades, the fact that you don't inculde the generation of the torque (or torque reaction) does not make it an invalid analysis, it gives highly useful results. It just leaves something to be solved elsewhere.
Patent offices are littered with designs for machines with similar principles to Jiff's. They all fail to completely bound the system. For Jiff's system the trick is being able to generate instantaneous torque, and maintain it at a known position, for others it is the moving of the mass (apparently without having to use a force to move it.) I personally favour the use of anti-matter to increase and decrease the mass throughout a cycle!
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Waspy, i reread post #87. Not knowing your background, your knowledge can only be judged by these posts - recanting newtonian physics is not a good start!
The problem in your analysis lies in the fact that you have not included the reaction to the mass tangential acceleration force in the central thrust bearing. So the forces acting at the central thrust bearing should be:
1. Motor torque to drive rotational accel/deccel.
2. Centrifugal reaction force.
3. Linear reaction to tangential accel.
Force 3 in combination with the tangential accel force is what creates the need for there to be torque 1. Rerun the analysis with this in place and you will find all the force impulse balances out over a cycle. The single rotor machine just sits there and shakes...
Physics makes you pay for everything!
The problem in your analysis lies in the fact that you have not included the reaction to the mass tangential acceleration force in the central thrust bearing. So the forces acting at the central thrust bearing should be:
1. Motor torque to drive rotational accel/deccel.
2. Centrifugal reaction force.
3. Linear reaction to tangential accel.
Force 3 in combination with the tangential accel force is what creates the need for there to be torque 1. Rerun the analysis with this in place and you will find all the force impulse balances out over a cycle. The single rotor machine just sits there and shakes...
Physics makes you pay for everything!
Last edited by Graviman; 19th Jul 2007 at 08:49.
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