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Author Topic: The sum of torque not at 0 ?  (Read 905 times)

Offline LB7

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The sum of torque not at 0 ?
« on: 24/05/2016 17:07:50 »
Look at the device at the last message post
« Last Edit: 25/06/2016 19:05:23 by LB7 »


 

Offline timey

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Re: The sum of torque not at 0 ?
« Reply #1 on: 31/05/2016 21:22:02 »
Aw... I'm really not qualified to comment, but if it's any consulation, I would if I was...
 

Offline impyre

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Re: The sum of torque not at 0 ?
« Reply #2 on: 01/06/2016 18:48:36 »
The problem with this post thus far (besides language) is that it's unclear what the physical constraints of the system are. It's entirely unclear what you hope to accomplish with this. What are you trying to prove? What's the problem or question? I can math, but I have no idea where your math is coming from. Simply put, I have no clue what's going on with any of this. It seems like it's being presented as a perpetual motion machine, but admittedly I'm unsure. In order to make this more clear you need to:
1) enumerate all axes
2) enumerate all fixed bodies
3) enumerate all discreet mobile bodies
4) enumerate all connections and constraints
5) describe all constraints on motion for mobile bodies relative to their point of connection to the root object (most likely a fixed body)
6) describe significant physical properties of all bodies (are they rigid? flexible?)
(IE: if a swinging arm is connected to a fixed body by a joint, does that joint allow movement in one, two or three axes? Does it slide? Is it degree-limited?)
It might also be helpful to provide a visual model that shows each part labelled as such.
 
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Offline impyre

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Re: The sum of torque not at 0 ?
« Reply #3 on: 02/06/2016 12:33:24 »
There should be a net torque on the disk. If a real model were built then a net torque would be present. The reason for this is that the balls or whatever would disperse the forces amongst each other, but the forces exerted on the container would not be equal at all points. You must consider that some force must be exerted on the balls to keep them in the container and in their present orientation. This force is exerted on them by the container itself; however, since the balls have an attractor they are not exerting force perpendicular to the surface as you suggest. They are exerting the majority of force in the direction of the attractor, which means the container must exert an opposing force to counter this. This opposing force could be thought of to originate from the geometric center of the interface between the balls and the container, but suffice it to say that it will *not* be applied from the axis. The difference vector between where this counter force must be applied and the location of the axis will result in leverage and torque, every time. The container will attempt to find the most stable configuration, which will occur with the center of mass of the balls is as close to the attractor as it can be.
You mentioned it was unstable without a motor, what I said above explains why. Where does this torque come from in your model? It appears to be provided by the red arm. The red arm will apply greater force to whichever side of the container attempts to protrude (the lower side in this case), thus correcting for the torque, but this results in a new torque being transferred down the length of the red arm to the red axis (and to your motor). The motor will have to do work to keep the container from righting itself.
The black arm can be used to generate energy to compensate for the energy spent at the red axis; however, due to mechanical inefficiency not all of the energy will be recovered. The net result is a loss of energy to keep this thing moving. Why spend that energy to move it at all? Does it do something useful besides suck up energy?
 

Offline impyre

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Re: The sum of torque not at 0 ?
« Reply #4 on: 04/06/2016 18:38:34 »
I hate to be negative, but people have been trying to do this for ages. When I was younger I even tried myself a few times. In my experience (personally as well as dealing with others), the basic laws of physics tend to hold true (especially in a classical sense where they excel in describing and predicting the kind of macroscopic mechanical behavior that you're trying to describe.) This simply cannot be done with classical mechanics. If anyone were to find/create something that tends to generate energy, that energy has to come from somewhere... even if we don't understand the physics of it (and that's being very generous in this case).

However, I think I can safely say that mechanical engineering is not only well understood and practiced across the world every day by many people. It's rooted in time-tested proven principles based on math and physics. This isn't quantum mechanics, it's just a complex mechanical design.

Just because complex mechanics is well-understood and reliable does *not* mean that it's always straightforward or simple. In my own cases (and often times with other people as well), misunderstandings tend to result from incorrect intuition or math that's more complex than it seems on the surface. You might "simplify" your model by making some assumptions, and this is often done in physics to make it easier for students to focus on learning one thing at a time; however, as an engineer you learn that these "negligible" variables that are often ignored for the sake of simplifying problems can sometimes creep up in unexpected or unintuitive ways to create problems.

In short, I think you're chasing a dead end. I'm simply trying to give you some advice here. I think you'll find that a physical model will not function the way you want it to, regardless of how convoluted the design is.
 

Offline LB7

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Re: The sum of torque not at 0 ?
« Reply #5 on: 22/06/2016 06:20:33 »
I studied the sum of energy of the device for a small angle like 0.001 rd for example. I studied only the horizontal forces here because the vertical force is at 0.

I supposed the wheel rotates and moves before the study of the sum of the energy
I supposed an external device force the wheel to turn and rotate without an acceleration like that it's easier to calculate the energy in/out.


1) enumerate all axes
The green axis is fixed on the wheel

2) enumerate all fixed bodies
The ground
The device that gives the force Fq

3) enumerate all discreet mobile bodies
All the device moves in translation and rotates clockwise like a wheel of a bike

The red wall
The outer circle of the wheel and the blue wall (blue color = one body)
N balls (small like molecules of water, just for simplify the calculations), without mass (simplify)
N springs, without mass (simplify calculations)
Gaskets (I don't drawn them)

4) enumerate all connections and constraints
The red wall can only turn around the green axis, the red wall is in contact with balls only, the red wall receives the pressure from the balls
Each ball is attracted by a spring from the center C
The device like that is unstable but I give the force Fq from an external device fixed on the ground.

5) describe all constraints on motion for mobile bodies relative to their point of connection to the root object (most likely a fixed body)
When the wheel moves and rotates, all the device turns and moves, the springs never lost their potential energy because the balls are always in the same relative position

6) describe significant physical properties of all bodies (are they rigid? flexible?)

All bodies are rigid except the springs
The springs and the balls are without mass
The wheel has a mass.
Each ball is attracted with the law 1/dē with 'd' the distance between the center of the wheel and the ball

The device:


The names of points:


The integrals:


All the device moves and rotates like a wheel of a bike (balls don't escape):


The energy:

« Last Edit: 26/06/2016 23:32:36 by LB7 »
 

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Re: The sum of torque not at 0 ?
« Reply #5 on: 22/06/2016 06:20:33 »

 

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