How to position compacted mass?

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Discussion Overview

The discussion revolves around optimizing the positioning of a compacted mass in the form of a cone with a spherical cap to counteract torque effectively. Participants explore the implications of varying densities within the mass and how these affect the center of mass, moment of inertia, and overall stability under applied torque. The conversation includes theoretical considerations and mathematical modeling aspects.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • Some participants propose that varying densities at different locations within the cone can help lower the center of mass and maximize counter torque.
  • Others argue that the goal of "taking on the most torque" is vague and suggest that a clearer definition of constraints is necessary for meaningful optimization.
  • A participant mentions that for a homogeneous cone, the moment of inertia is maximized when height approaches infinity and radius approaches zero, while for heterogeneous density, the greatest density should be at the base.
  • There is a suggestion that a full matrix solution involving eigenvalues and moments of inertia is needed to analyze the problem comprehensively.
  • Some participants express uncertainty about how to weight the different densities effectively when torque is applied.
  • One participant questions the completeness of the problem statement and requests a free body diagram to clarify the setup.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the optimal approach to the problem, with multiple competing views on how to define and solve the optimization challenge. There is ongoing debate regarding the clarity of the problem statement and the necessary constraints for the proposed solutions.

Contextual Notes

Limitations include unclear constraints such as fixed volume or mass, and the need for a complete free body diagram to fully understand the forces at play. The discussion also highlights the complexity of optimizing for torque without a clear definition of the desired outcomes.

colinbeaton1
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My goal is to fight the max amount of torque with the weight by having different densities at different places and by keeping the z center of mass low.
I need to find the answer out in terms of the three angles, and the final answer must not have a substituted angles such as 45 degrees.
I need an ideal density function in terms of x,y,z. In terms of height and radius from vertical axis.
The main function is the cone, and the details are here
http://www.wolframalpha.com/input/?i=cone+moment+of+inertia&lk=4&num=5&lk=4&num=5
At the bottom of the cone there is a spherical cap, details here
http://www.wolframalpha.com/input/?i=partial+sphere

Use mass m, and radius r, the angles, and the equations and please show me all the work so I can fully understand for later use.
 

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Engineering news on Phys.org
angle three can be equal to 0 or more
 
colinbeaton1 said:
My goal is to fight the max amount of torque with the weight by having different densities at different places

What does this mean?
Your attachment looks like the cone may be hanging like a pendulum? Is the diagram on the right what you think the force will cause?
 
Sorry about the picture, the force is on the wrong side. Just pretend the force is on the other side.

What I want to do is create a 3d cone with a 3d spherical cap, and in order to take on the most force times an arm or torque, I want to have a the perfect densities at different locations in the mass.

I want an optimization formula. Gravity is in the picture too.
 
colinbeaton1 said:
What I want to do is create a 3d cone with a 3d spherical cap, and in order to take on the most force times an arm or torque

It's still not clear what this means.
"take the most torque" is vague and would normally be interpreted as 'What geometry and material is required to minimise deformation or failure due to torque" or similar.

Are you trying to minimise the angular acceleration due to an applied torque? Obviously you want to maximise the moment of inertia, but without knowing your constraints (which are unclear; fixed volume? fixed mass? etc) or what exactly you are trying to do it's difficult.
Can you provide a complete free body diagram?

For a cone of homogeneous density the MOI about it's peak is maximised when h →∞ and r→0 (where h = height of cone & r = radii of it's base)
For a cone of heterogeneous density and fixed dimensions the MOI about it's peak is maximised when the greatest density is concentrated at the base.
These are trivial conclusions and can be proved via calculus but should be intuitive; concentrate the mass as far from the axis of rotation as possible.
 
I want the mass to be able to counteract a maximum amount of torque, T1.

1) The cone with sphere end, the object, is unmoving until a torque, T1, acts on it.
2) We take mass of object, m, and play with the density, inertia, and center of mass to optimize an equation to find what values of what we need to optimize the objecct itself.
3)For example, we could make the density of mass increase in the object of mass m as we go down the object, to make the center of mass lower, to create more counter torque. We could also make it more or less dense with respect to the radius.
4)Basically we have 3 or 4 or more densities of mass at different places in the object, summing up to mass m
 

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Also, the next part to take note of which I do not know is how to weight the masses differently because the actual time we need the mass is when it has T1 acting upon it.
 
colinbeaton1 said:
I want the mass to be able to counteract a maximum amount of torque, T1.

1) The cone with sphere end, the object, is unmoving until a torque, T1, acts on it.
2) We take mass of object, m, and play with the density, inertia, and center of mass to optimize an equation to find what values of what we need to optimize the objecct itself.
3)For example, we could make the density of mass increase in the object of mass m as we go down the object, to make the center of mass lower, to create more counter torque. We could also make it more or less dense with respect to the radius.
4)Basically we have 3 or 4 or more densities of mass at different places in the object, summing up to mass m

You'll end up with a point mass, m, of infinite density at the bottom centre of the rounded base. The rest of the cone will have a density of zero (or negative if you forget a constraint in your working).
All roads lead to Rome;
billy_joule said:
concentrate the mass as far from the axis of rotation as possible.

https://en.wikipedia.org/wiki/Moment_of_inertia#Calculating_moment_of_inertia_about_an_axis
colinbeaton1 said:
Also, the next part to take note of which I do not know is how to weight the masses differently because the actual time we need the mass is when it has T1 acting upon it.

I can't understand this.
 
We need a full matrix solution for the problem in the picture. 3d matrix. Eigen values, moments, inertia, forces, etc. I have not done this sort of matrix before, please guide me.
 

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  • #10
Is that the entire problem statement word for word? It seems incomplete and there's no mention of variable density, do you have the actual diagram? Where is the spring connected to the cone? ie does h,r,a affect the torque about the rotation axis due to the spring?

You'll need to do a good free body diagram that includes all the given information.

It still seems fairly trivial, it's clear maximising for T will lead to h →∞, r →∞ and a→0 (and l → 0).
 

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