Animate/Mobile Pivot Point

[max-antinone]

I'd like to make a rig that has a movable pivot point, and I haven't been able to figure it out.

It's easy enough to use groups to make a rig with multiple specific pivot points (if, say, the character swings from his hand at one point), but I want to be able to move the pivot so I can arbitrarily rotate the character from any point I wish.
Specifically, I have a setup that can calculate the center of mass given a series of weights in space.  I want to constraint objects with a mass attribute to a character's skeleton so that the character can always rotate from their center of mass, even as their CoM changes when they move their limbs around.

I've tried several tricks with grouping, parent constraints, utility nodes, and expressions, but I've yet to find a setup that still works once I rotate the system.

[joojaa]

you can do this, unfortunately its VERY convoluted. because it needs 3 vectors of information to work out, And because of dg rules its not easily groupable into one move.

Also its near unusable because its so timeconsumning to key, honest*. Google for animating a cube rolling.

*also since its a path integral you can only ever animate it going forward or all your later keys will crap up.

[daikath]

I hope it's not too late, but I found a way to do thi,  in the connecion editor connect the translate vector of a locator(not the seperate, X, Y or Z floats) and hook it up to the RotatePivot of the object you want to have a mobile pivot.

Then parent the locator to the object so it moves with it and it works fine.

[joojaa]

Yes but you must also somehow handlöe rotate pivot offset if you intendt to key it!

[daikath]

A simpler idea I for having a pivot point shift during animation for example a shot where your character first runs and then dives is to have two seperate controls for the initial center of gravity. Place them where it the center of gravity is and  going to end up. Parent constrain both to your animation object and key the wheights of the constrains to go totally from the first object to the other object during the shiftt.

But autodesk really needs to make a pivot constrain option.....

[70madmax]

the thing is very simple, i often use it.

1) parent all the controls you want to rotate to something(a group for example), this will be the 'master'
2) rotating the master all is done

when you want to move your 'master pivot point' you have to:

1) save all the children positions
2) move the 'master'
3) move all the children the opposite of the master

this way your master control has moved, and your controls are in the same position they were before

boring to do by hand, simple to do with a script, and it works.

[daikath]

That works with stepped keys Max, but it wont give you a nice transition in a smooth animation curve. You can't gradually move the pivot point, or center of mass like it would in real life if you were to run and then dive or flip.

Using different parent constrains does mean you have to set the different directions at least beforehand, but since those are really only the hip or chest, you take two different Center of Gravity controls to both of em (even can make them move along for the most part). Another control between them could even be a fun visual way to control the influence of the different parent constrains.

That way you can change the effective placement of the pivot with a nice smooth gradual curve instead of one harsh stepped key.

[joojaa]

And thest why theres 2 vectors to animating pivot positions, and thats WHY its hard to do this. Its donet actually help the animatrors if the data is in one extra node or not.

See thing is everybody usderstands what the pivot position is about. but the residual compound of the pivot ofsset is a bit incomprehensible data to animators. Its very easy to animate tough, its just very hard to cope with. All you need is.

for object you want to animate pivot for. open channel control add the following attributes to the keyable list:

.rotatePivotTranslateX;
.rotatePivotTranslateY;
.rotatePivotTranslateZ;
.rotatePivotX;
.rotatePivotY;
.rotatePivotZ;

Tough for pure practiocalöity i suggest you include the scale pivot in the list also! (this make sit easier to move the pivot about later)
Thast it. your now set. to move the pivot just hold down the key 'd' while obejct is selected. then key away. Now youd still need to udnerstand what your doing and that in my experience is a bit problematic.

constraining the pivot, now this is a bit tricky. see pivot is a core dag info. Now the core of dag can not be cyclic.

Then parent the locator to the object so it moves with it and it works fine.

Well this dont really work. see dag MUST compute in order. So the locator MUST be computed before the node it controlls. Thsi is a bit tricky since parentting makes the locator resolve after the parent. (and it MUST ALLWAYS DO THIS) The net effect is that thepivot is actually offset in time by one step in compute order. THis si extremely bad bad bad.

Now you can do this. However this still leaves the pivot offset. Wich is a bit hard to understand. Thsi all sint sucha  problem however one other thing is.

theres a visual clue dscreppancy going on. See your manipulator and the pivot will allways coencide on top of each other so knowincg wich you have selected is rather clumsy to arrange. THis is a much bigger problem. tnhan actually constraimning the data to somewhere.

But autodesk really needs to make a pivot constrain option.....

Actually i dont think that would be wise, theres however a much better thing they could do instead and that is off node aliases. THsi could solve the thing elegantly but it would solve several other known rigging limitations of maya by allowing data to be shared across nodes for keying purposes across different selections.

Now however thing is a parent constraint chain CAN be use dto move the pivot its just not the most productive workflow. The biggest problem si still keeping track of where the firgging pivot is at times. This just convolutes things over whats needed.

PS: pivot locations can slo be emulated by adding 3 different translates instead of 1.

[daikath]

Thanks for all this info Joojaa, I'll definately keep trying to attempt to do stuff with this info.

You could make the position of a pivot between two parent constrains visible though by padding in a control object between them which has a attribute which is at zero when it is placed at the hip control and at one when it is at the chest control. It could even drive the constrains.

But I'll try and keep working with your info for a more interactive solution :).

[joojaa]

Just remeber thet the object thet dives the location MUST be a sibling of the object in question. Its kindof easy if the object is actually only used for rotation but not so much once it isnt. In wich case you need a buch of matrix multiplyu nodes to cope.

Yeah it can be done but ist not a pretty picture.

[molemansd7]

you can try this too...
http://www.creativecrash.com/maya/downloads/scripts-plugins/character/c/zv-parent-master