Adding a secondary motion factor to a rig using constraints
By Michael Malinowski
||This tutorial will go through the process of setting
up secondary motion and skin movement on characters using constraints as
apposed to the use of softbodies etc.|
I will start from the very beginning, so we can see the problems and benefits. So to begin with lets create a cube, duplicate it, move it and scale it, then repeat the process so you create something similar to the following image.
Now enable constrain compensation, and choose constrain pose whilst having cube2 selected, then select cube1, set the blend to 0.5 ( this is the strength of the constraint), now choose cube3, select the constraint and select cube2 ( set this blend to 0.3) and so one, so cube2 is constrained to cube1, cube3 is constrained to cube2, and cube4 is constrained to cube3.
Now if you rotate cube1 you will notice that the constrained cubes all follow behind in a delayed motion, so already were beginning to make use of secondary motion. However, we can quickly spot a problem with this setup.
we wanted to set this secondary motion on the arms of a dinosaur, so that
when it walks its arms bounce up and down automatically, we could do this
using the above setup, however we would have no control over the arms as
they are now constrained to another object which gives us little scope for
||So lets being the fun part, we need to create another object, I am using an implicit sphere, although it really doesn't matter what time of object you use for this. We will then position constrain the new object to the upper spine, making sure you have compensation enabled, set the blend to whatever value you feel fit, for this I will set it to 0.5 then set it to a custom slider later so the values can be easily changed.|
the dinosaur moves you will notice that the object we just constrained
moves with an offset. All we need to do now, is make the new constrained
object a child of the spine so its all part of the same hierarchy, then
cut the parenting between the spine and the arms, and instead make the
arms a child of the constrained object.
|In this quick example video file you can see the dinosaur walking.
(excuse the rough animation, I only spent quite literally 60 seconds
setting the keyframes) but you can see the amount of extra movement you
get, all of which is entirely editable, and all the arms, head and tail
are still keyframable giving the animator just as much control as he/she
would have without the secondary motion. From all that motion, only 3
objects were keyframed! The rest was all automated.|
With this in mind you can begin to think of the possibilities this gives!
click the image on the left to view the file.
if you have encountered any problems with this tutorial then please email . firstname.lastname@example.org and i will try to resolve it. This was created using Softimage|XSI 3.0, but should run down to 2.0.
hope this helps.