Basic Skeleton

 Introduction

This is a guide to build a basic bipedal skeleton for your 3D models. I will cover how to setup your character before you rig, how to build the skeleton of your character, how to create handles to move your character, and how to paint your skin weights on your character.

Pre-rig

To start, we will switch our model to wireframe only. To do this, look to the top of your view window and select the see-thru 3D box.

Next we will setup clusters. Clusters will not be part of the main rig, but will act as a guide for where we place our joints.

To begin, turn your model into vertices and find the hip of your character. Select two vertices, one in front of the model and one in back of the model and relatively in the same height. Next, make sure your files tabs are set to “Animation” and go Create Deformers > Cluster. This should create a “C” in the middle of your model. Repeat this process for the spine, the left arm, and the left leg. The spine should have about six clusters. The arm should have a cluster for the shoulder, the elbow, the wrist, the palm, and three clusters for each finger. The leg should have a cluster at the hip, the knee, the ankle, the base, and the toe. You should have something that resembles a stick figure.

 Joints

The pre-rig work is done and now we can focus on creating the actual skeleton. To start, add your model to a layer and turn that layer off . Go to Skeleton > Joint Tool, hold down “v” (snaps your joints to vertices aka the clusters you made), and slowly click on each cluster on your spine. Hit “Enter” and your spine his created. Repeat this process for your arm clusters and leg clusters.

Now that half of your skeleton is created, select the arm joint chain and Skeleton > Mirror Joint (Options Box if necessary). Repeat that process for the leg joint chain. Now we have a full skeleton and need to combine the arms and legs to the spine. To do this, go to Window > Outliner and middle mouse drag the leg joint chains onto the hip joint and arm joint chains onto the middle spine joint.

Now that we have a full skeleton, we can get rid of the clusters. Go to Edit > Delete All by Type > History.

Handles/Constraints

With a full skeleton, we need a way to control the skeleton. We achieve this through handles, which we create with Nurbs Circle. Go to Create > NURBS Primitives > Circle or click on the Curves tab and select the circle.

Create a circle big enough to fit outside  your model so you can select it later on. Now hold down “v” and move the circle until it is in the center of the hip joint. Repeat this process for all the joints  in the upper half of your model (we will worry about the legs in the next part).  Now select all your handles and go to Modify > Freeze Transformations. This sets all handle values to zero, making it easier to reset all controls while animating.

Now that we have created the handles, we need to constrain the joints to the handles. There are five basic constraints:

·         Point

·         Aim

·         Orient

·         Scale

·         Parent

There are only two contraints we care about: Orient and Parent.

Let’s begin with the hip handle. First select the handle and then shift/command select the hip joint. Next go to Constrain > Parent > Options Box. Make sure maintain offset and click “Add.”  A Parent Constraint allows you to translate and rotate your skeleton. Repeat the same process for the rest of your handles but go to Constrain > Orient > Options Box this time. An Orient Constraint allows you to only rotate your skeleton, making it ideal for the spine and arms. You should now be able to move your handles and your skeleton will move.

Now that the upper body is complete, we will build handles for the lower half. We will only need two handles, one for each foot. We will now use an IK Handle to move the legs. IK Handles allows you to move a joint chain from the bottom of the chain to the top.  Go to Skeleton > IK Handle. Select the top joint of the leg (secondary hip joint) and now select the ankle joint of the same leg. Your skeleton should now be an orange color and have a line running through the chain.

We now constrain the leg to the handles. We repeat the same process from the upper body, but instead of selecting the joint we will select the IK Handle. We will also use a Parent Constraint to constrain the joints to the handles.

We now have a fully operational rig.

Weight Painting

Now that we have a fully functional rig, we need to attach it to the model. Before we do, let’s do some organizing. Select your entire skeleton, and add it to a new layer. Do the same for your handles. This will allow you to turn them off if you want.

We now select the skeleton and then select the mesh, Go to Skin > Bind Skin > Smooth Bind > Options Box. Inside this options box are a variety of features, we are only concerned with two: Skinning Method and Max Influences (Fig. 9).

When it comes to Skinning Method, I usually use Dual Quaterrion. It gives the model a nice flex when you rotate it to a certain point. You could also use Classic Linear, but it does not add that flex.

When it comes to Max Influences, we really only want our vertices to be controlled by three joints, so I set the influences down to three.

We can now click “Bind Skin.” Test out your character and see how he moves.

When you moved your character, the mesh deformed in areas you did not want it to move. Luckily this can be fixed by a process called Weight Painting. There is two ways of painting skin weights, but I will only be discussing one: Paint Skin Weights Tool.

Paint Skin Weights Tool allows use to paint the influences on our model. To access this, right-click your model and select “Paint Skin Weights Tool.” Your model will now turn almost entirely black except for some white and grey coloring around the hip.

The white area is the area influenced by the main hip joint. So if you rotate your hip control that is the area that will deform. We can switch between the joints, as well as set the value of influence (0 to 1, 0 being nothing and black, 1 being influenced and white) in the tool settings that appears when you select “Paint Skin Weights Tool."

With this tool, we can weight the skin on our model to move properly with the skeleton.