Group Post – Maya Bone Skeleton Systems

Patrick Hayes, Ben Koontz, Dalton Witham, Bo Hubbard, Sam Joe Carl, Nick Hansman

When we first chose Maya Bone Skeleton System we had not the slightest clue of what it was or how it worked. We had been under the assumption that it possibly had something to do with the skeletal structure of a building. Though that initial idea was wrong, what we did find out about Maya Bone Skeleton Systems was so much more than we could have expected. We were able to find a real-world application of the program in the Academy Award winning short film The ChubbChubbs! and an instruction manual that related to the movie as well. Using the manual, we were able to learn more about Maya Bone Skeleton Systems and constructed our own character from the short film. (below is a YouTube link to the animated short film)

Maya Bone Skeleton Systems is a tool used by animators to help prepare geometries created in Maya for movements and animation. The skeletons built in the program provide a framework and structure that will regulate the movement of a character or geometry. However, Maya Bone Skeleton Systems is less about actually moving around and animating geometry than it is about creating a structure in order to control and create logical and appropriate movements later in the animation process. Without the skeleton system, the character or geometries would be useless to the animator.

Maya Skeletons are made by drawing a series of joints to form a skeleton chain, also referred to as a joint hierarchy. These chains create a continuous hierarchy of joint nodes that are parented to the join before them. The geometry or character that will be moving using the skeleton system is generally created/built first. Once the character is built, the placement of the joints become easier. The first join that is placed in a joint chain is known as the Root Joint or the Parent Joint. This Parent joint is the top joint in the chain hierarchy. Each subsequent joint in the chain is then considered a child joint to the parent and moves as the parent joint is moved or rotated. In most cases, many different joint hierarchies are created within a geometry for maximum control of the character later in animation. For example, a characters two legs would be considered a different joint chain. Despite being different chains, the legs are part of a complete skeleton and are thus joined together  by the hip joint. The hip is the parent to both the left and right leg joint chain hierarchies. This method of parenting multiple chains is called Parenting Skeletons.

Most of the animation of joints is done using rotation because that is the appropriate and natural movement of joints. Each joint has its own axis and the most desirable orientation of each joint is critical in order for animations to move correctly later in the animation process. Joints whose rotation axis, in both single hierarchies and multiple chain hierarchies, face the same direction will all rotate appropriately and logically according to one another. The most basic type of movement is called Forward Kinematics and it was already briefly described above, but to reiterate, the parent joints control the child joints and any movement that the parent joints make the child joints follow.

However, Forward Kinematics creates a problem for animators when they are attempting to generate a more complicated movement sequence. The problem stems from the principle that child joints have to move and follow parent joints as they move. For example, if you are animating a bipedal character and this bipedal character is walking, when the character plants its foot on the ground it should logically stay there until it is lifted up again to take another step. However, when using strictly Forward Kinematics, any movement that occurs in the hips or legs of this character (joints that are higher up in the joint hierarchy) will cause the planted foot to move along with and follow its parent joints. Inverse Kinematics is the solution to the problems that are posed by Forward Kinematics. With the use of an Inverse Kinematic Handle (IK handle), a child joint can be allowed to move or stay put, and the IK handle will calculate the movement of the parent joint and adjust the child joints according to what has already been assigned to them.

Forward Kinematics is useful for basic movements such as the swinging of a person’s arms while walking. Inverse Kinematics are useful in more complex movements like picking things up, jumping and planting a foot on the ground. Because of their different uses, both processes are used when animating any character and this is called IK/FK Blending. In most animation processes many IK handles will be used (and then blended with FK handles) and built upon a skeleton system in order to give the animator more logical control over how a geometry will move. These handles can be prioritized within Maya and can create a hierarchy of potential movements for joints and joint chains when rotated or translated.

Unfortunately, the amount of time it takes to build custom geometries and characters just to be used by the Bone Skeleton Systems makes it a tough tool for architects. It could be possible to use the program to generate a walk-through of a proposed building using different characters, but again there are other programs to do that much quicker. Maya Bone Skeleton Systems are a much better tool for digital designers, game developers, and movie animators.

Link to online video tutorial that we created for our presentation that failed to load for said presentation.

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