Tutorial 3: Animating a Biped with Footsteps

Lesson 3: Gymnastic Motion Flips with Ballistic Tension

The basic jump has already been set up for you. It is a basic eight-footstep backwards jump produced by the Create Multiple Footsteps dialog. The last pair of steps have been moved in to reduce the jump height of the final hop.

Loading the motion file

  1. Open cs3_tut03_flip1.max.

  2. Select the biped.

  3. Go to the Front viewport and play the animation using Biped playback.

    The basic jump

    Notice that the upper body appears mechanical, although the biped leans slightly into the jump and bends its knees in anticipation of the jump.

    You will add a flip to the motion.

Adding a flip

Adding a flip involves setting rotation keys for the body by rotating the center of mass object (Bip01) while the body is in the air. If the feet are not touching the ground, rotating the center of mass rotates the entire body. If the feet are planted on the ground, rotating the center of mass rotates only the upper body. The feet remain on the ground.

You want the biped to rotate 360 degrees during the flip. You must define at least two turning keyframes in the air to make the biped flip all the way around in the same direction.

Producing the first flip

  1. Click Body Rotation on the Track Selection rollout to select the center of mass rotation track.

  2. Click Lock Selection Set.

    When working with objects like the center of mass that are close to other objects, lock your selection to avoid accidentally selecting another object. This is especially true if you will be switching viewports or zooming and panning.

  3. Move the time slider to frame 31.

  4. Right-click Select and Rotate.

    The Transform Type-in dialog is displayed. This lets you enter precisely the transform you wish.

  5. In the Offset Local area enter a Local rotation of -94 degrees in the Y axis field.

    The biped rotates onto its back.

    Use Transform Type-in to rotate the biped.

  6. On the KeyInfo rollout, click Set Key to set the turning key.

  7. Move the time slider to frame 42.

    The biped rotates back as a result of continuity with other keys. The next step will fix the rotation.

  8. Rotate the biped -196 degrees about the Local Y axis.

    The biped is upside down with its feet about to come back down.

  9. Click Set Key.

    That completes the first flip.

  10. Close the Transform Type-In dialog.

    You can use the body keys you just created to produce the second flip. Since the second flip is similar to the first, you can copy body positions from the first flip to equivalent frames in the second flip.

Producing the second flip

  1. Move the time slider to frame 31.

  2. Click Copy Posture on the Keyframing rollout to copy the body rotation to a buffer.

  3. Move the time slider to frame 74.

  4. Click Paste Posture to replace the body rotation at this frame with the rotation in the posture buffer.

    The biped body rotates into the same position at frame 74 and at frame 31.

  5. Click Set Key.

    Do the same for the rest of the flip frames.

  6. At frame 42, click Copy Posture.

  7. At frame 85, click Paste Posture.

  8. Click Set Key.

  9. Move the time slider to frame 0, and play the animation.

    Now you have two complete flips in the jump sequence.

    Two flips (shown using ghosting)

  10. Unlock the selection set.

  11. Save your motion data by clicking Save File on the General rollout.

  12. Save the file as myflip2.bip.

Verifying your work

  1. Click Load File to load another biped motion file, then choose cstudio\tutorials\tutorial_3\flip2.bip.

    This motion file contains the same movements that you created in the last procedure. You can use it to check your rotations.

  2. Play this version to verify that your motion sequence is accurate.

    You can continue the tutorial with this prepared motion file to insure that you are starting from a known point. If your motion sequence is correct and you would rather use your own file, you can reload myflip2.bip and proceed with the tutorial.

    In addition to setting keys for the body in the air, we must also alter the rotational keys of the body about its center of mass on the ground to create the impression that the body is preparing for the back flip by whipping itself backwards just before lift-off. Because the feet are planted on the ground, rotating the center of mass rotates only the upper body.

    The whipping action will also involve the spine and arms, but you'll begin by setting the body's rotation keys about the center of mass.

Creating the basic windup (or angular momentum) for the flip

  1. Select the center of mass.

  2. Move the time slider to frame 0.

  3. Click Body Rotation Track on the Track Selection rollout.

  4. This turns on Select and Rotate in the Main toolbar.

  5. Right-click Select and Rotate.

  6. In the Rotate Transform Type-In dialog, in the Offset Local group, specify 35 degrees as the rotation for the Y axis.

    The biped bends forward. Because the feet are planted on the ground, only the upper body is affected.

    Only the upper body rotates

  7. Click Set Key.

    Don't forget to set the key. If you're used to animating in 3D Studio MAX you can turn on Animate instead to set rotation keys automatically.

    Next, you will add rotation keys to the center of mass at five different frames.

    Tip: You can also use the transform manipulator to select and rotate about a chosen axis. Watch the coordinate display at the bottom as you rotate in the viewport. For entering exact values however, Type-in Transform is faster and precise.

At Frame...

Do this...

10 

Rotate the biped 30 degrees about the Y axis, then click Set Key. 

20 (lift-off) 

Rotate the biped -25 degrees about the Y axis, then click Set Key. 

53 (touchdown) 

Rotate the biped -15 degrees about the Y axis, then click Set Key. 

63 (second lift-off) 

Rotate the biped -30 degrees about the Y axis, then click Set Key. 

96 (second touchdown) 

Rotate the biped 15 degrees about the Y axis, then click Set Key. 

  1. Play the animation.

  2. Save your motion data by clicking Save File on the General rollout.

  3. Name the file myflip3.bip, and click Save.

Verifying your work

Adjusting the Body Motions

You have made the biped flip. The next steps are designed to improve the quality of the movement and make it look more natural. You do this by working on one body track at a time.

Adjusting the first flip

  1. Click Select By Name, select all the biped spine objects from the selection list, then lock the selection.

  2. Click Rotate.

  3. On the General rollout, turn on Bend Links mode.

  4. Turn on Animate and go to frame 0.

  5. Rotate the spine object 30 degrees about the Z axis to bend the biped forward.

    Frame 0

  6. Move to frame 20 and rotate the spine -30 degrees about the Z axis.

    The status of both feet is displayed as Lift in the General rollout.

  7. Move to frame 42 and rotate the spine 50 degrees about the Z axis.

    Frame 42

    Notice that the biped's back tucks in. This alters the biped's position during the first flip. Next, you'll alter its position during the second flip.

Adjusting the second flip

  1. Move to frame 53 and rotate the spine 20 degrees about the Z axis.

    This is when the biped lands after the first flip. The status of both feet is Touch.

    Frame 53

  2. Go to frame 63, and rotate the spine -20 degrees about the Z axis, so the biped's spine is thrown back in preparation for the next flip.

    At frame 63, the status of both feet is Lift.

    Frame 63

  3. At frame 42, click Copy Posture to copy the position of the entire spine at this frame.

    Note: Copy Posture copies selected biped objects, Copy Pose copies the entire biped.

  4. Go to frame 85 and click Paste Posture.

    The biped changes from a straight posture to a tucked posture.

  5. Turn off Bend Links mode.

  6. Go to frame 0 and play the animation.

    Upper Body bending added

    Notice that the biped's upper body now bends as though it was being used to power the motion.

  7. Save your motion data by clicking Save File on the General rollout and save as myflip4.bip.

Adjusting the legs

  1. Unlock the selection and move to frame 37.

  2. Be sure Animate is still on.

  3. Right-click in the viewport and choose Rotate.

  4. Select a biped foot.

  5. On the Track Selection rollout, click Symmetrical Tracks to select both feet.

  6. Rotate the feet about the Z axis approximately 50 degrees, so the toes point up a little more.

  7. Right-click and select Move. Use the Transform gizmo corners to move the feet so the knees move between the hands.

    Move the feet to bend the knees.

  8. At frame 80, the equivalent frame in the second jump, move the feet again so the knees tuck and the pose compresses.

    Use the file flip4.bip for reference and backup.

    Until now, the biped's arms have been relatively immobile. In a real flip, the arms would begin the flip. In general, arm movement is timed to the spine movement. For the first jump, the arms begin moving at frame 0 and finish moving at frame 20. They accelerate through that period.

Rotating the arms

  1. Make sure Animate is still on.

  2. Right-click and choose Rotate.

  3. Select an upper arm (Bip01 R UpperArm).

  4. On the Track Selection rollout, click Symmetrical Tracks to select both arms.

  5. At frame 20, rotate the arms -150 degrees about the Z axis.

    This makes the arms nearly vertical.

  6. At frame 10, the midpoint of the rotation, click Set Key to lock the rotation.

  7. Move the time slider to frame 0 and rotate the arms 60 degrees about the Z axis.

    This places the arms just behind the back.

  8. Play the animation.

    Tip: Turn off Real Time Playback on the Time Configuration dialog to see every frame during playback.

Adjusting the arm swing

At this point, the motion is fine, but the arms should accelerate more. To do this, you'll copy the arm posture from the first third of the motion onto the arms in the middle of the time sequence. The result will be slower motion in the first half of the sequence and faster motion in the second half.

  1. At frame 6, double-click an upper arm to select the entire arm.

  2. Click Symmetrical Tracks to select both arms.

  3. Click Copy Posture.

  4. At frame 10, click Paste Posture.

  5. Play the animation.

    Swing the arms faster.

    The arms now accelerate as they move up. At the beginning of the second flip, the biped is already traveling faster than in the first flip and there is less need for arm movement.

  6. At frame 53, click Set Key to lock this arm posture.

  7. Deselect the entire arms.

  8. Select an upper arm object.

  9. Click Symmetrical tracks.

  10. At frame 63, the lift-off point, right-click in the viewport, and choose Rotate.

  11. Rotate the arms -150 degrees about the Z axis so the arms raise up.

Moving the head

In general, the head will bend with the spine as it tucks, but will be more vertical when the feet are planted.

  1. At frame 20, make sure that Animate is still on.

  2. Select and rotate the head -40 degrees about the Z axis.

    As a result of spine and center of mass rotations, the head is thrown back too far at frame 42.

  3. At frame 42, rotate the head 40 degrees about the Z axis.

    Biped head rotation at frame 42

  4. At frame 53, rotate the head -12 degrees about the Z axis.

    Frame 53 is the touch down point, where the biped would be looking up from the tuck.

    Frame 63 is where the head would be thrown back as part of the jump.

  5. At frame 63, rotate the head -40 degrees about the Z axis.

    Head thrown back

    The biped is looking straight up at the sky.

  6. At frame 71, rotate the head 15 degrees about the Z axis.

  7. At frame 85, the same point in the flip as frame 42, rotate the head 40 degrees about the Z axis.

    This tucks the chin into the chest between the arms.

    Chin tucked in

  8. Turn off Animate, go to frame 0, and play the animation.

  9. Save your motion data as myflip5.bip.

    You can load flip5.bip to check your changes.

Adding the Twist

Now that you have a good-looking jump and flip, it's time to add a twist. The easiest way to accomplish this is to rotate selected footprints and let the biped automatically adapt.

Twisting the footsteps

  1. Turn on Footstep mode on the General rollout.

  2. Region-select footsteps 2 and 3.

  3. In the Top viewport, drag up on footstep 2 to rotate the footsteps -180 degrees about the Local Z axis.

  4. Right-click and choose Move.

  5. Move footsteps 2 and 3 about the Y axis, in line with the other footsteps.

    Rotate and move the footsteps.

  6. Play the animation.

    You'll see the biped do a half twist in the first jump. It will also do a backward half twist in the second jump. You'll fix that next.

  7. Click Select and rotate and select footsteps 4, 5, 6, and 7.

  8. Drag up on footstep 6 in the Top viewport and rotate the footsteps -180 degrees about the Z axis.

  9. Click Move and drag the footsteps so footstep 6 is on top of footstep 0.

  10. Play the animation again.

    The biped does a half twist in the first jump. The second jump is a simple flip ending with the biped facing the opposite direction.

  11. Load flip6.bip to verify that your motion sequence is accurate.

    In the following procedure you'll move some of the footsteps to simulate a jump from a height down to a lower level.

    You will use a Track View selection technique to select footsteps 0 and 1 because they are covered by footsteps 6 and 7.

Adding height to the flip

  1. Make sure Footstep mode is still on.

  2. Right-click and choose Track View Selected.

    Track View opens. Bip01Footsteps are displayed in the track as blue and green blocks.

  3. Region-select the blue and green footstep blocks numbered 0 and 1 to select the footsteps.

  4. Close the Track View window.

  5. Click Move, and drag footsteps 0 and 1 up 80 units about the Local Z axis.

    Move the footsteps up.

    You can now use regular region selection in the viewports to select and move the remaining footsteps.

  6. Select footsteps 2 and 3 and move the footsteps up 40 units about the Local Z axis.

  7. Select footsteps 4 and 5 and move the footsteps up 15 units about the Local Z axis.

    Footsteps 6 and 7 remain at ground level.

  8. Turn off Footstep mode and play the animation.

    The biped jumps from a height, twists, lands on a lower level, continues the jump, flips, and comes to a stop on the lowest level. The levels make the acrobatics more believable and interesting.

    Jump and twist from a height

  9. Load flip7.bip if you want to verify that your motion sequence is accurate.

    To add to the realism, you could create a complete scene by constructing a series of platforms under each set of footsteps.

    Dr X flips out

Next

 

 

 


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