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Another flour sack test

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I was doing a little research on flour sack exercises and saw one post that the tabs, or arms and legs of a flour sack are more for conveying emotion than for a means to create motion. That sort of resonated with me, so I revisited the rig on my flour sack and added some dynamic constraints to the bones for the "arms", then ran a quick test. The result is below.

 

The big question now is, if the tabs, tassels, whatever, are not for motion, then how to we motivate a flour sack to scoot across the screen?

 

 

 

https://youtu.be/-hrv65lValY

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I've always thought of the flour sack like this setup...the "arms" can be thought of as arms or as ears depending on what is needed for the shot (and can be used both ways in the same clip in my mind). I made a very simple animation with this rig here: https://www.hash.com/forums/index.php?showtopic=33048&p=377570

 

Hope that helps, Paul.

 

 

 

 

 

flour_sack_rig.png

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The big question now is, if the tabs, tassels, whatever, are not for motion, then how to we motivate a flour sack to scoot across the screen?

 

It would be my understanding that we can look to the bouncing ball exercise for the answer to that as the ball can be motivated to move (act or react) without appendages.
Another way of saying that might be to consider weight (and therefore squash and stretch) and the forces such conveys.
For instance, when compressing downward (squashing) the object (flour sack or whatever) is storing energy that is then released upon release (stretch).
Add to this the idea of torsion (another way of storing energy) and additional movement can be represented.
In the flour sack I suppose the first thing to consider would be what type of movement is desired.
In other words, what motivates the flour sack to move.
As with the bouncing ball it could be simply a matter of gravity.
If the flour sack is not sentient in any way then the environment might be the catalyst for change.
For instance, if the flour sack is on the top step of a flight of stairs and the sand inside is shifting to reach proper blance then that might force the flour sack to proceed down the steps. The same would be true of sloping terrain... the weight of sand shifting and adjusting the center of gravity.
If the flour sack is seen to have a mind of its own then a degree of suspension of belief is assumed in that the sand might not fall entirely as it would with respect to gravity but is being constrained in such a way as to appear to 'walk', jump or perform some other activity. Even in these cases though I think a high degree of interaction with the environment would be ideal with continual displays of action/reaction. Again, this depends on what you want the flour sack to do. There might be an unseen hand that initially tosses the flour sack onto a teeter totter which in turn launches another flour sack into the air where it performs a somersault.
Consider where the center of gravity is with regard to the flour sack and set up some initial condition (or force) where the flour sack is set out of balance. This would then require the sand inside the sack to move and to seek a proper distribution/balance.
I suspect that a lot of flour sack animation starts with an initial force being generated by an unseen hand. The action seen thereafter following the rule of 'an object in motion continues in motion'. We just never see the initial force being exerted. If the flour sack is sentient though its reaction to a given situation provides the initial movitation. An example of this from fellow A:M user Paul Daley whose "Sack Attack" had live action dogs chasing a flour sack, the sack was motivated to move by the dogs who were chasing it.

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I've always thought of the flour sack like this setup...the "arms" can be thought of as arms or as ears depending on what is needed for the shot (and can be used both ways in the same clip in my mind). I made a very simple animation with this rig here: https://www.hash.com/forums/index.php?showtopic=33048&p=377570

 

Hope that helps, Paul.

 

 

 

 

 

 

You know, I never thought to run the arms and legs up the side like that. Might have to play around and see if it works for me!

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I figure the tabs are ambiguous. They can be whatever you need them to be to make the shot work.

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For instance, if the flour sack is on the top step of a flight of stairs and the sand inside is shifting to reach proper blance then that might force the flour sack to proceed down the steps. The same would be true of sloping terrain... the weight of sand shifting and adjusting the center of gravity.
If the flour sack is seen to have a mind of its own then a degree of suspension of belief is assumed in that the sand might not fall entirely as it would with respect to gravity but is being constrained in such a way as to appear to 'walk', jump or perform some other activity. Even in these cases though I think a high degree of interaction with the environment would be ideal with continual displays of action/reaction. Again, this depends on what you want the flour sack to do. There might be an unseen hand that initially tosses the flour sack onto a teeter totter which in turn launches another flour sack into the air where it performs a somersault.

 

Rodney when i first read your response I instantly got an image in my head of a giant finger poking the poor flour sack in the back and tipping it over, ala Monty Python. But then that spun off onto a weird tangent and turned into the idea of a hill, then a sledding hill, then alas, two months later, the following short.

 

https://youtu.be/NxVc4PwtvPk

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I enjoyed that!

 

giant finger poking the poor flour sack in the back and tipping it over

 

In animation we can do just about anything. :)

 

I'd imagine that if a giant finger poked at a flour sack, the sack's weight would be such that it wouldn't tip over unless already precariously perched somewhere.

The idea being that most of the sand/weight is near the bottom of the sack and so the finger would simply redistribute the sand at the top of the sack. (we could actually have a go at animating this!)

This is the same premise of what might happen if someone were to push on a regular human being whose is balanced. The push might cause some movement but if the base of the human is well balanced then only the upper extremities would react.

 

Consider the law of motion that states "a body in motion tends to stay in motion".

If the flour sack is already in motion (i.e. unbalanced) then it will be more likely to tip over.

If in balance (equilibrium not in motion) then chain reactions will effect the object part by part depending on the construction of the object.

As such I can easily see where a giant poking finger might press into the sack... leaving an indentation... and slightly moving the top of the sack... but not effecting much of the rest of the sack.

I guess we'd have to consider the weight of that sack.

When thinking of it I definitely get a sense of the weight of a really heavy flour sack.

 

Rather than make suggestions concerning this present animation I"ll suggest telling another story with the sack.

Keep animating! :)

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I enjoyed that!

 

giant finger poking the poor flour sack in the back and tipping it over

 

In animation we can do just about anything. :)

 

I'd imagine that if a giant finger poked at a flour sack, the sack's weight would be such that it wouldn't tip over unless already precariously perched somewhere.

The idea being that most of the sand/weight is near the bottom of the sack and so the finger would simply redistribute the sand at the top of the sack. (we could actually have a go at animating this!)

This is the same premise of what might happen if someone were to push on a regular human being whose is balanced. The push might cause some movement but if the base of the human is well balanced then only the upper extremities would react.

 

 

In the spirit on Monty Python, I give you the finger poke.

 

floursack_mp.avi

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