Tutorial 4: Animating Bipeds interacting with Objects

Lesson 1: Dribbling a Basketball

This example animates the biped's hand and a basketball to simulate the biped bouncing the ball. The ball is animated on its own, bouncing up and down. When the ball is at the height of its bounce, it controls the hand through inverse kinematic blending. When the ball strikes the ground, the ball and the hand are not connected, and the hand is animated independently. You'll animate IK Blend on and off to create this effect.


  1. Open cs3_tut04_bouncestart.max.

  2. Play the animation to see what happens.

    The biped bounces the ball 5 times while walking forward.

Understanding the Keyframing

Use Key mode to understand the structure of the animation.

  1. Select the ball.

    Keys appear in the track bar.

  2. Turn on Key mode.

  3. Move to each key using Next Key or clicking the arrows on the time slider.

    The ball strikes the ground at frames 15, 39, 58, 78 and 101.

    The ball is at the top height of its bounce at frames 0, 30, 48, 67, 89, and 111.

  4. Select the biped's right hand (Walk01 R Hand).

    Keys appear in the track bar.

  5. Open the IK Key Info rollout and play the animation.

    The fields in the rollout blink rapidly because IK Blend is animated.

  6. Move to each key, looking at the IK Blend field.

    IK Blend fluctuates between 1 and 0.

    Observe the pattern of the keys in the track bar. There are groups of three or more keys followed by a single key.

    The groups have IK Blend set to 1, but the single keys have IK Blend set to 0. The groups also have Object Space selected. Sphere01 (the basketball) has been designated as the Object Space Object.

    Note that only one Object Space Object can be defined for the hand. You cannot change from one Object space object to another during the animation.

Adjusting the Basketball's animation

  1. Turn on Animate.

  2. Select the ball.

  3. At frame 30, move the ball up and closer to the biped's body.

    The hand follows the position of the ball because the hand is locked into the object space of the ball.

    Tip: If the hand does not move with the ball, select the hand and verify that Object space is turned on in the IK Key Info rollout.

    Hand follows ball

  4. At frame 0, move the basketball down.

    The hand moves with the ball because since IK Blend is set to 1 and the ball is the designated Object.

    Note: If you move the ball too far it leaves the hand behind.

  5. Move the basketball up so it is in contact with the hand.

  6. Rotate the spine so the biped crouches over.

  7. Move the basketball down so the dribble is low.

    Rotate the spine.

    Moving the basketball repositions the hand when the IK Blend is set to 1 and the basketball the object.

    If you move the basketball while IK Blend is set to 0, the ball will not affect the hand.

  8. At frame 14, set IK blend to 0.

  9. At frame 16, set IK blend to 0

  10. At frame 15, move the basketball.

    Nothing happens to the hand, because IK blend is 0.

Animating the dribble

The basketball bounces one time more than the biped dribbles it. You'll set up the last dribble to see how this works.

  1. With Animate still turned on, go to frame 111.

  2. Select the right hand.

  3. Move the hand up out of the way.

    You'll be moving it again, so it doesn't matter where you move it.

  4. Select the basketball.

  5. Move the ball in front of the biped, at about waist height.

  6. Zoom in the Perspective, Left and Front viewports so you can see the biped's hand.

  7. Rotate and move the biped's hand so it is in contact with the ball. Rotate the fingers so the hand cups the ball.

  8. In the IK Key Info rollout, change IK Blend to 1 and turn on Object.

    Sphere01 is already designated as the Object Space Object, so you don't need to select it.

  9. Raise the ball.

    The hand moves with it.

    If you move the time slider back and forth, you'll see there's still more work to do.

  10. At frame 109 move the hand down so it is just above the basketball, change IK Blend to 1, and turn on Object.

  11. At frame 113 move the hand down so it's just above the basketball, change IK Blend to 1 and turn on Object.

  12. Move to frame 117.

    You need to set IK Blend back to 0, or the movement of the ball will continue to influence the hand. But the fields are not available because there is no key set.

  13. In the Key Info rollout, click Set Key.

    This sets IK Blend to 0 and turns on Body space.

    Move the time slider to see the movement.