Rigging for Moosah & Chub
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.
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.
Under the position options window, lower the Blend Weight (the lower it is, the bone structure will be more flexible).
In this same window, set the Coupling to soft, rather than hard.
Branch select the bone's root (by middle clicking), duplicate it, and bring the duplicate down so the duplicate root is between the effector and the null (image a).
image a
image b
image c
Now make the duplicate root the child of the original effector (image b).
You can easily double the length of your chain by branch selecting the original root, duplicating, and parenting the duplicate to the proceeding effector. The more bones you have, the more fluid motion you can achieve (image c).
Now time to test out the chain. Translate the original root in your view; the chain should lag behind based on the blend weight percentage you set.
You can adjust this be selecting the appropriate effector and opening its Position Constraint window, which is easily found under 'Selection' on the right side of the screen. In some cases, you may find it more believable to have a higher Blend Weight on effectors closer to the root then gradually decrease towards the end of the chain.
If any of the roots are rotated, the following chain links will adjust accordingly.
This allows for easy adjustment to fit meshes. Once it's drawn and setup correctly from one angle, adjust the rotation of the roots as needed in another. This chain is what I used for the canopy branches on my model. The original root was the child of the hip bone on the beast, so once he was animated the canopy bounced to his steps.
I used single bone soft constraints for hard items that needed secondary motion like the skulls, jawbones, water bag, horn, etc. Using a single bone soft position constraint for these objects allowed them to pivot at their designated spots (where the root was placed) and to keep their volume. For my model, there were quite a few accessories that were weighted to single or small soft constraint bone chains, and had their roots being children of the hip bone.
After setting up this type of chain a few times, you'll get used to the procedure and will start to understand how and why it works. Keep in my you can even use the basic position constraint to get certain effects you want.
To setup the spear quiver I simply used a combination of soft position constraints and specific weighting. The spear basket was weighted 100% to the yellow implicit sphere, which was a soft position constraint of one of the spine bones. The top section of the spears were weight 100% to the green implicit, which was a soft position constraint of the yellow implicit. The spears' grip was weighted appropriately so that it stayed with the shaft. I also set up a couple more soft position constraints with the blue and red implicates and weighted appropriately to give the spears' feathers more life (red constrained to blue which was constrained to green).
This similar method was used for the dreamcatcher and antler sinew as well.
You've noticed that these soft constraints will interact real time. This is because its based on the previous frame for its calculations. If you happen to be rendering on multiple machines, you may need to bake in the animation of the constraints.
Do this in the animation toolbar by plotting all transformations for all the soft constrained objects.
After the transformation is baked in, you'll have to remove the constraints from everything to make sure it does overwrite the animation already baked in. This may take a while depending on the number of constraints you have setup.
The only other complicated feature of the rig on Moosah and Chub was the Syflex setup, which was created for the two reigns, flag and canopy cloth. Having the Syflex cloth react with the canopy branches and loops involved a huge combination of Syflex nails and position constraints, but Syflex is a whole other setup.
Thanks for reading, and happy rigging!
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