Making a Hand Follow an Object

Interacting with Objects

Creating the Illusion of Weight

 

Autodesk 3ds Max Tutorials > Character Animation Tutorials > Biped Beyond the Basics > Interacting with Objects > 

Making Feet Follow Objects

In this lesson, you’ll make a character ride a skateboard.

In practice, you could accomplish this animation by linking the skateboard to one of the biped’s feet and animating the entire biped. However, this would make it extremely difficult to animate the biped’s upper body leaning and dipping as he rides the skateboard. If you did so, every time you moved the biped’s foot or leg, the skateboard would skitter and slide unnaturally.

You can’t link the biped’s feet directly to the skateboard with Select and Link. These body parts are already linked to the legs, and linking them to another object would cause them to become disengaged from the legs and the rest of the body.

Instead, you’ll use IK linking to make the biped feet and body follow an animated skateboard. With this method, you can animate the upper body leaning and turning without interfering with the motion of the skateboard. This feature makes it easy to animate a character doing any motion where the feet need to stay stuck to the apparatus while the body moves freely, such as pedaling a bicycle or skiing down a slope.

Set up for this lesson:

1. Open the file skating_start.max.

   

   This scene features Wilson on a skateboard.

2. Play the animation.

   The skateboard follows a path, but Wilson doesn’t go with it. You’ll work with Wilson’s biped to make him ride the skateboard.

3. Choose the named selection set Wilson Mesh, and hide the selected objects.
4. Choose the named selection set Wilson Biped, and click Yes on the warning dialog to unhide the biped.

Position the feet:

1. Go to the Motion panel.
2. Go to frame 0.
3. In the Front viewport, zoom in on the feet.
4. Turn on Auto Key.
5. Rotate each foot so it sits parallel to the top of the skateboard.

   

Link the feet to the skateboard:

In order to link the feet to the skateboard, each needs a key set at frame 0. You have already created keys for the feet by posing them on frame 0. If you hadn’t, you could use the Set Key button on the Key Info rollout to set keys for each foot/leg.

1. Select a foot or leg.

   You can select any part of the leg or foot to link it to the skateboard.

2. On the Motion panel > Key Info rollout, expand the IK bar.
3. Click Select IK Object, and click the top portion of the skateboard.

   The object name Skateboard Top appears to the left of the Select IK Object button.

4. Choose the Object option just above the Select IK Object button.
5. Change IK Blend to 1.0.
6. Select any part of the other foot or leg, and repeat these steps to link it to the skateboard.
7. Play the animation.

   

   The biped tries to follow the skateboard, but he’s not very successful. The legs extend as much as they can, but the skateboard moves away and the biped's center of mass stays in the same place.

   To make the entire body go along with the skateboard, you’ll link the center of mass to it.

Link the COM to the skateboard:

The center of mass object (COM) is the only object in the biped that isn’t linked to other objects in the biped. It can be linked to any object with Select And Link to make the entire body follow along with the object.

1. Select the center of mass object, named Wilson Biped.
2. On the Main toolbar, click Select And Link.
3. Link the center of mass to the skateboard.
4. Play the animation.

   The entire biped moves with the skateboard.

   

Animate the upper body:

The linking method you’ve used allows you to animate the upper body freely without interfering with the skateboard motion.

1. Go to frame 0.
2. Make sure Auto Key is turned on.
3. Pose the biped in a crouch, as if ready to turn a corner on the skateboard. Move the center of mass downward to bend the biped’s knees, and move it horizontally to shift the biped’s weight. Rotate the spine to make the biped lean forward, and pose the head and arms.

   

   TipTo rotate the legs outward, rotate the calf and not the thigh. This will rotate the legs while keeping the feet in place.
4. Go to frame 60 and change the pose slightly. You can move the center of mass to shift the biped’s weight, turn his head, or move his arms to different positions.
5. On frame 120, change the pose again.
6. Play the animation.

   The biped rides the skateboard, leaning and dipping to keep his balance.

See the animation on the character mesh:

1. Select the named selection set Wilson Mesh, and click Yes to unhide the mesh.
2. Select the named selection set Wilson Biped, and hide the selection.
3. Play the animation. Cowabunga!

   

   You can see a finished version of this animation in the file skating_complete.max.