Action Constraint Alternatives?

Question

I wanted to give the Action constraint a try by making a simple translation/rotation animation, using a bone as the guide for the translation via the copy location constraint.

What I didnt know at the time, doing this directly after seeing the video, is that the Action constraint doesnt actually animate anything other than the transformation keyframes of the bone.
(This makes sense thinking about it, since it's only accessing the data of the bone directly not any other attached data such as constraints)

Video Link

Is there any alternative way to do this? Primarily for the sake of animating something on a single slider (ie. single key frame pair) such as the Evaluation slide as you mentioned.
Drivers maybe, though I wouldnt see how that works with the other influences/head-tail/etc. sliders that require different values?

Answer 1 · 2024-11-01T01:04:40Z

Wayne Dixon replied November 1, 2024 1:04am

This is an interesting test that you are trying out Pascal.

The action constraint is being overridden by the copy location constraint - which is why only the rotation is working in your final test.

From what I understand about what you are trying to do..

You want these bones to slide along the length of 2 different bones, yeah?

I don't think this type of thing will work with the action constraint because it would require secondary constraints to be animated.

I don't think this data can be captured by the action constraint.......unless you see up a bunch of mechanisms that converted this switching into a bone transformation.

So other solutions might be to set up a spline that has a control vert at each guide bone joint and then parent those verts to the bones.

Then on your other bones, clamp them to the spline with a constraint, and then drive the movement along the spline with an action constraint or a driver.

But then dealing with the rotation is another problem to solve.

This reminds me of the Treasure Chest project, that had the retractable cannon inside. (It opened like a sliding bread box)

This required A LOT of mechanism to make it easily animatable with a single control.

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Answer 2 · 2024-11-01T09:52:31Z

replied November 1, 2024 9:52am

What I was trying to do, was Translate and Rotate the three bones along the bendy bone (could have been a normal bone with the way I did it, as it only created linear Translation between head/tail of the bendy bone).

I swapped around the order to see how the Copy Location affected the Action constraint, but since the Action constraint doesnt capture the influence values it didnt change.

But yes your right it would most likely require multiple mechanism bones now that I think about it performing different actions with drivers in order to try and bring that into a single property.
Though interesting to explore, do you happen to know of any content creators that further explore this type of complex setup -> simple control rigging that I could take a look at for further study?

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Answer 3 · 2024-11-02T10:06:41Z

Wayne Dixon replied November 2, 2024 10:06am

You can get the bone to follow the bendy bone. You just need to enable the follow b-bone button.

As for setting this up to a single control. You can do it with some copy loc and copy rot constraints, but you will need to drive the Head/Tail value and the sequential constraint.
ie - it follows 1 bone from the head/tail, then the next bone from head to tail when the influence on the first bone turns off.
You just need to be really clever with the curve mapping on each part you are driving.

As for content creators doing this type of stuff.............ummmmmm.................not that I can think of.
Maybe a guy called Pascal (but not just quite yet haha)

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