Tutorial 4: Animating Bipeds interacting with Objects

Lesson 2: Climbing a Ladder Using IK Blend

It takes a lot of steps to create a freeform animation because you're animating the feet and hands without any automation. Once you learn a technique, you repeat the same sequences over and over for each limb to create the keyframes.

In this lesson you'll load a file that is partially animated and you'll create the animation for just one of the arms. Normally, you would then repeat the steps for the other limbs.

Setup

  1. Open cs3_tut04_ladder_start.max.

  2. Play the animation.

    Let the animation loop while you watch the movement of the green hand. It grabs the ladder to support the biped as he steps up on the green foot.

    You'll make the left hand grab the rung and then slide up the rail as the biped climbs.

Creating the first poses

  1. Turn on Animate.

  2. Select Bip01 L Hand.

    At frame 0, the arms are at rest. The first pose is at frame 19.

  3. At frame 19 move the hand forward and slightly up, as if the biped's about to shake hands.

    The arm at frame 19

  4. At frame 30 move the hand so the left fingers just touch the ladder.

  5. Rotate the hand about the Y axis so the hand is perpendicular to the ladder rung.

    The arm at frame 30

Grabbing the ladder

You'll position the hand to grab the ladder. The fingers will rotate, the hand will have IK Blend set to 1, and you'll put the hand in the Object space of the ladder rail.

  1. At frame 36 select the hand.

  2. Move the hand so the palm is flush with the ladder rail, near the third rung.

  3. In the Top viewport, move the hand to the right of the ladder rail.

  4. Rotate the hand so the palm is flush with the ladder rail.

    Watch the Top and Perspective viewports as you move the hand.

  5. To select all the fingers, double-click the hand to select the hand and all the fingers, then hold down the ALT key and click on the hand.

    Now all the fingers are selected.

  6. In the Top viewport, rotate the fingers about the Z axis so they curl to grab the ladder.

    You can also adjust each finger individually.

  7. Deselect the fingers and select the hand again.

  8. In the IK Key Info rollout, change IK Blend to 1.

  9. Change from Body to Object Space.

    The Object Space Object, Box06 is now active.

    Move the time slider to see the animation. The biped appears to grab the rail.

    The arm at frame 36

Sliding the hand up the ladder

The hand is locked to the ladder rung at frame 36 so it stays as the rest of the biped moves in the frames that follow. To slide the hand up the ladder, you'll use a trick. You'll move the hand in the Reference Coordinate System of the ladder.

The arm at frame 49

  1. Choose Select and Move in the Main Toolbar, and make sure Bip01 L Hand is selected.

  2. In the Reference Coordinate System selector in the Main toolbar, choose Pick, then select Box06.

    The Transform gizmo changes. You can move the hand so it remains aligned to the ladder rail.

  3. At frame 45, move the hand up so it is farther up the rail.

    The hand now immediately starts to slide up the rail from frame 36 to frame 45. It should grip the ladder for stability for a few frames before the slide begins.

  4. Hold down the SHIFT key and move the key on the trackbar from frame 36 to frame 39.

  5. This clones the key from frame 36 to 39.

  6. In Key Info, set the Tension and Continuity to 0 at frames 36 and 39.

  7. Move the time slider to play the animation.

    The hand grips the rail starting at frame 36, then begins the slide from frames 39 to 45.

  8. At frame 49, move and rotate the hand so the gripping fingers stay wrapped around the ladder.

    The movement takes place in the Reference Coordinate System of the ladder rail (Box06), but the rotation does not. Each transform can use a different coordinate system. Selecting one system for position doesn't affect the system for rotation.

Opening and Closing the Grip

At frame 61, the green foot is planted on second rung. The hand will release its grip on the rail.

  1. At frame 61, select all the fingers.

  2. Rotate the fingers so they loosen their grip.

  3. Move the hand out so it comes off the rail a little.

    At frame 80, the blue toes touch the top rung. The fingers grip again.

  4. At frame 80 select all the fingers.

  5. Rotate the fingers back into a grip.

  6. Move and rotate the hand so it grips the ladder at the top of the rail.

    The arm at frame 80

    The green foot is planted on top of box at frame 115. This is the last frame in which the hands grip the rungs.

  7. At frame 115, rotate the hand about the Y axis, so the hand pivots on the top of the rung.

    The arm at frame 115

  8. Hold down the SHIFT key and move the key on the track bar from frame 115 to frame 122.

    This clones the key from 115 to 122.

  9. In the Key Info rollout set Continuity and Tension to 0 for keyframes 115 and 122.

    This locks the hand in place until frame 122.

Releasing the grip

  1. At frame 126, select the hand again and set a free key.

    Setting a free key sets IK Blend to 0 and turns on Body Space (it turns off Object Space).

  2. Move the hand off the ladder.

    The hand is not affected by the ladder any more.

  3. Select the fingers and rotate them to relax the grip. Rotate the hand about the Y axis so the hand is pointing more towards the ground.

    The arm at frame 126

  4. At frame 154 rotate and move the hand so it is loosely outstretched.

    Biped steps onto the blue foot.

    The arm at frame 154

  5. At frame 169 select the entire right arm.

    In the Keyframing rollout, choose Copy Posture, then Paste Opposite.

  6. The biped stops, rests his hands on hips, and preens.

    Hands on hips, fingers curled back

    Everything you just did was also done on the opposite hand. The feet also were animated by creating IK Blend keys to lock and unlock them to the rungs.

    Use Animating a Walk Cycle with IK Constraints and Animating a Leap with Freeform Animation to animate the feet and hands working with pivot points.

  7. Save your work as myladder1.max. If you want you can open cs3_tut04_ladder_end.max to compare your work to the correct animation.

Linking the center of mass to an object

When the hand is locked to the ladder, any animation of the ladder affects the hand. If you want the movement of the ladder to affect the entire biped, use the Select and Link tool.

You'll look at a scene from the production"Pool Tools" to see this in action. When the ladder in the scene swings from side to side, the biped will swing with it.

Setup

  1. Open cs3_tut04_ladder_swing.max.

  2. Play the animation.

    The pool guy climbs the ladder.

    The animation of the pool guy climbing the ladder has already been done. The ladder has also been animated, but there is no link between the two.

    The ladder swings, but the biped stays put.

    You will lock the hand down and then link the biped's center of mass to the ladder.

Making the hand grab the rung

  1. At to frame 431, turn on Animate.

  2. Select the left hand and move it close to the ladder rung.

  3. Select the Bip01 L Finger0.

  4. Right-click and choose Rotate.

  5. Rotate the finger about the Z axis, to grasp the ladder.

  6. In IK Key Info, set a sliding key.

    This sets IK Blend to 1, which locks the hand in Object Space.

Making the biped swing with ladder

If you play the animation you'll see that the ladder still swings, leaving the biped behind in the air. You'll use the Select and Link tool in the Main toolbar to change this.

  1. Choose Select and Link from the Main Toolbar.

  2. Click on the biped's center of mass. When the icon changes, drag to the ladder and link.

    Linked center of mass moves biped with ladder

  3. At frame 451, select and move the center of mass.

    The hand is locked, but the rest of the biped can be changed.

    Note: If you move the center of mass far enough, the hand leaves the ladder. If you override the IK limits, the forward kinematics take precedence.

  4. Rotate the center of mass about the X axis, so the biped swings a little bit.

    Move and rotate the center of mass until the biped is in position.

    Hand is locked, the rest of the biped moves

  5. Repeat the process at frame 482, moving and rotating the center of mass, so the hand remains on the ladder and the body swings in the opposite direction.

    Biped swings with the ladder

    To finish the animation, you'd have to repeat this process to match all the keys as the ladder continues to wobble back and forth. You can do that for practice if you like.

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