User Guide > Learning > Characters > Kinematics

Heel-to-Toe Foot Setup

In this lesson you will create a leg setup that lets you animate how a foot rolls from heel-to-toe. This motion helps anchor the character to the ground and create more realistic walk and run cycles.

To simplify the manipulation of the foot, you will create a control hierarchy that lets you position and rotate the foot, while rolling the ball and toe areas.

This lesson contains the following sections:

Part One: Create the Leg Bones
Part Two: Create the Foot Control
Part Three: Set the Leg Kinematics


Part One: Create the Leg Bones

To create a heel-to-toe setup, you will need to start with bones that define the thigh, calf, ankle and foot. At this point, you will not need any Kinematics. These can be added when they are needed later.

1. Set up the workspace

Set up with two side by side views. Point at the front view and then the right view. Link the ortho views so that the grids match. Zoom out then pan the view until the ground level is near the bottom of the screen.

Open the snap controls and set cp points to a stronger value. Turn on snapping.

2. Create a Subnetwork

In the network view, press tab > Subnetwork. This will create an empty subnetwork operator which will be used to contain the character. This will help you make sure that all the part are contained in a single network which will make it possible to create a Digital Asset of the character later.

Press i to go into the subnetwork Operator. This is where you will draw the bones.

3. Draw the Leg Bones

Press tab > Character > Bones. Make sure that Kinematics is set to No Kinematics.

In the Front view, place the first bone in the front view about 15 units above the ground. Now click four units over and one unit down to place the hip joint. In the right view, click at the knee then the ankle, ball and toe. Use the grid to align the points.

4. Rename the Bones

Now rename the bones as pelvis, thigh, calf, ankle, and foot. Notice how in Houdini you are naming the bones and not the joints. This means that the final click defines the end point of the foot bone instead of the position of the toe joint."


Part Two: Create the Foot Control

To create the reverse foot setup you will build a hierarchy of null objects which will be used to control the kinematics of the foot bones.

1. Create the Heel Control

Create a Null object. Name it heel_control then move it to where the heel of the foot would be. Make sure that it is aligned in both views.

2. Create the Toe Control

In the Viewer pane, press tab > Copy. Click on the heel_control object then RMB-click to accept. Next, Transform the object so that it snaps to the foot’s toe. Rename the object toe_control.

3. Create the Ball Control

In the Viewer pane, press tab > Copy. Click on the heel_control object then RMB-click to accept. Next, Transform the object so that it snaps to the foot’s ball. Rename the object ball_control.

4. Parenting the Control Objects

Click on the toe_control object and in the Parameter pane turn on Keep position when parenting. Now parent the toe_control object to the heel_control object in the network view.

Repeat for the ball_control object then parent it to toe_control.


Part Three: Set the Leg Kinematics

Originally, you drew the bones without any kinematics. You can now go back and add Kinematics to the bones of the leg and foot.

1. Add Inverse Kinematics to the Leg

Press tab > Bones and in the set Kinematics to IK with Twist Affector. Move into the viewport then Ctl-RMB click and select Add Kinematics from the menu. Click on the thigh_bone then RMB-click to accept. Next, click on the calf_bone then RMB-click to accept.

Now an IK chain runs from the hip to the ankle. An end effector has been added to the ankle and a twist affector has been added to the knee.

2. Parent the Twist and Goal

Rename the end effector to leg_goal and parent it to the ball_control object."

Next rename the twist affector to knee_lookat and parent it to the heel_control object. Transform the twist effector cube to a point in front of the knee.

3. Test the Setup

With the Transform tool, select the heel_control object and Rotate it to see the leg and foot rotate with the control hierarchy. Now Move the heel_control up to further test the setup. The controls are moving the leg but the ball and toe are not yet working.

Undo back to the start position.