I knew rigging my Moosah and Chub model would be quite the project, but once I understood some of Softimage XSI's rigging features it went pretty smooth. For this model I created a whole series of soft constraints, which can give the effect of secondary action, gravity, wind resistance, etc. These soft constraints will run realtime and can be used to create automated rigs. With my model, I was able to animate the beast and have the rider and accessories all react believably to just the beast's movement.
Looking at the entirety of the bone system might be a bit chaotic, but once I show the process for a single section it'll look a lot simpler. To start things off, you will need to check a couple options under the animation toolbar: Create - Skeleton. Make sure to check "SI|3D Skeleton Drawing" and "Align Root to First Bone When Drawing". The first option properly sets up the parenting for the bones that is needed for this technique (places the effector under the last drawn bone instead of the root). The second option just makes things visually cleaner.
CLICK TO ENLARGE
Time for the construction of the soft constraint; choose "Draw 2D Chain" and create a single bone pointing downwards, then end picking.
Create a null and place it just below the effector.
Make the null the child of the root.
Select the effector and constrain its position to the null.
