Biped is a 3D Studio MAX system plug-in that you access from the Create panel. Once you create a biped, you animate it using the Biped controls on the 3DS MAX Motion panel. Biped provides the tools you need to design and animate the motion of characters.
The biped structure has a number of properties designed to help the animator.
Joints on the biped are hinged to follow human anatomy. By default, the biped resembles a human skeleton and has a very stable Inverse Kinematics hierarchy. This means that when you move a hand or foot, for example, the corresponding elbow or knee will orient itself accordingly, and produce a natural human posture.
When you rotate the biped spine, the arms maintain their relative angle to the ground, rather than behaving as if they were fused to the shoulders. For example, if the biped is in a standing position, arms hanging at its sides, when you rotate the spine forward, the biped's fingers will touch the ground rather than point behind it. This is a more natural position for the hands, and this speeds the process of keyframing the biped. This feature also applies to the biped head. When you rotate the spine forward, the head maintains a forward-looking orientation.
Using the Move transformation tool on the 3DS MAX toolbar allows you to position the biped arms, legs, and center of mass.
Using the Rotate tool on the 3DS MAX toolbar allows you to rotate any biped object.
Using the Bend Links tool will rotate all of the spine objects simultaneously. This helps you to create posture keys for the biped. Biped playback is fast even on slower systems, allowing you to judge motion accurately.
If you want to keyframe your character with the mesh visible, use the 3DS MAX Freeze command to keep the mesh visible but unselectable. As you keyframe the underlying biped, the mesh follows the biped to animate the character, allowing you to see exactly how the mesh will behave as the biped limbs are positioned.
Moving or rotating the Biped center of mass (COM), an object shaped like a diamond in the pelvis area, positions or orients the entire biped. The center of mass uses three tracks to store motion keys: Body Vertical, Body Horizontal, and Body Rotation.
Body Vertical and Body Horizontal keys have additional parameters for gravity and balance, referred to as Biped Dynamics.
Body Vertical keys have Dynamics Blend and Ballistic Tension, respective parameters that control gravity and the amount of knee bend when a biped lands after an airborne period. These parameters only apply for lift-off and landing keys on either side of an airborne period. In an animation containing footsteps, an airborne period is an interval of time when neither of the biped feet is on a footstep. In a footstep animation using Biped Dynamics, you won't have to create Body Vertical keys for the apex of a jump or for the lowest part of the landing period; the Biped Dynamics will automatically calculate a trajectory for the center of mass. Gravity plays no role when a character is walking. In an animation containing footsteps, walking is defined as the biped having at least one foot on a footstep at all times.
Body Horizontal keys have a parameter called Balance Factor. Balance Factor, whose parameters are stored in the center of mass horizontal track, helps the animator by automatically shifting all of the biped limbs to naturally position the character's center of mass, over the feet when the spine is rotated. You can actually see the biped pelvis moving away from the center of mass object if the spine is rotated. This relieves the animator of having to set extra keys to simulate the character's balance. Balance Factor positions the biped for you.
There are two primary methods used in creating biped animation: Footsteps Method and Freeform Method. Each method has advantages, and you can convert from one method to the other, or you can use a combination of both techniques in a single animation.
In the viewports, footsteps represent support periods in space for the biped feet. Moving or rotating footsteps in space is done in the viewports. In Track View, each footstep appears as a block that represents a support period in time for each of the biped's feet. Moving footsteps in time is done in Track View. The footstep position and orientation in the viewport controls where the biped will step.
There are three ways to create footsteps for the biped. The first way is to place footsteps individually, or one at a time. The second way is to invoke Biped's multiple footstep creation tools to create a walk, run, or jump animation. The third way is to extract footsteps from raw motion capture data.
A key advantage of the footstep method is the natural adaptation of the biped that occurs when the footsteps are edited in time and space. Editing footsteps in the viewports allows you to reposition all of the footsteps to move the entire animation. In Footstep mode, stride, length, width, and direction can be changed quickly for an entire animation and the biped automatically adapts. Using the Footsteps Show/Hide button on the Display rollout, all footsteps can become visible. Move the footsteps in the viewports to position them for proper ground collision with the terrain object. For example, if the biped toes are rotated for the Lift key at the last frame of a footstep (to create more toe curl as the character walks) the leg automatically repositions itself to maintain foot contact with the ground (footstep).
These adaptations speed up the process of creating and editing animation for the biped. If necessary, the animator can prevent biped adaptation by using the Adapt Locks parameters on the Animation Properties rollout.
Within a footstep animation, there can be four foot states: move, touch, plant, and lift. These correspond with the state of the biped feet in relationship to the footsteps. Use the foot state displays in the General rollout to determine the state of the biped feet when you are editing the biped foot or leg keys. Foot states are used on the Set Multiple Keys dialog to select multiple keys in Track View.
A freeform animation contains no footsteps; instead it relies on the transforms of the biped body objects and center of mass. Use Freeform for motions like swimming or falling where footsteps are not necessary. If you are a familiar with creating all of your keyframes manually to animate a character, you may want to use the freeform method exclusively.
To start a freeform animation, turn on the 3DS MAX Animate button and start positioning the biped. Or you can leave the Animate button off and use the red set key buttons to create keyframes.
You can also create freeform animation by importing motion capture data and choosing freeform rather than footstep.
Tip: Take advantage of both methods by combining footsteps and freeform animation. You can create a freeform period for any airborne period between footsteps. A freeform period replaces the ballistic motion calculated using the GravAccel value with a user defined spline motion.
If you are using footstep extraction with motion capture data, you often need a freeform interval to accommodate falling or tumbling motion in the data. The Fit to Existing option on the Motion Capture Conversion Parameters dialog allows for a combination of both methods. Extracting footsteps from motion capture files eliminates sliding feet, a common problem with motion capture data.
Note that while you can add a freeform period to a footstep animation, you cannot add a footstep period into a freeform animation. If you want to add a footstep animation to an existing freeform, you can use the motion flow editor to create a script that sequences the footstep with the freeform.
Footstep and Freeform animations use the same IK constraints and extensions. This means that in a footstep animation, you can now edit keys to change footstep duration. By definition, a footstep is the start and end of a sequence of IK constraints in World Space with an IK Blend value greater than 0. Deleting and inserting keys or changing IK space or IK blending alters footstep duration.
In cases involving edits that alter the length of ballistic intervals (when a biped is airborne), the software ensures that there is a vertical key occurring at the lift-off and touchdown frames. This calculates the correct ballistic motion, so vertical keys are automatically inserted if not present.
There are three types of IK keys you can create: planted, sliding and free keys.
Planted keys have an IK Blend of 1. They are joined to the Previous IK Key and are in Object space, rather than Body space. Planted keys lock the foot or hand to the ground, or to any object.
Sliding keys have moving IK constraints. Sliding footsteps are created if there is a moved IK constraint occurring in the footstep interval. In a footstep animation this means that the foot can be placed anywhere, even though there is a footstep icon. Footstep icons can be thought of as gizmos rather than the absolute location of a foot. Sliding keys have an IK blend of 1, and are in object space, but are not joined to the previous IK key.
Free keys have an IK blend of 0, and are in body space. They are not joined to the previous IK key. Free keys have no IK constraint.
IK constraints are implemented with a pivot-based system. This allows you to pivot a hand or foot around a selected pivot. For example, in a walking motion you can select a pivot on the heel of a foot and rotate the foot around it,. You can then shift the pivot to the ball of the foot.
The way that Biped Dynamics affect the biped center of mass is discussed earlier in this topic. Spline Dynamics is an alternative method of keyframe interpolation. If you are starting a new animation, use the Animation Properties rollout to select the method you want to use. Spline Dynamics will be most familiar to new users. Selecting this method and creating new footsteps generates Body Vertical keys using Spline Dynamics for interpolation; Balance Factor and Gravity are turned off. You can convert from one method to the other by selecting one or all of the Vertical Center of mass keys in Track View and setting the Dynamics Blend parameter to 1 for Biped Dynamics, or 0 for Spline Dynamics.
Motion Capture Import, Motion Flow Mode, and Footstep creation tools are designed to increase your output.
Motion Capture: Typically, you will not use a complete motion capture file in its entirety unless you specifically capture sequences you need for your production. Once you are familiar with the motions in the files that you have, you can join together the motions that you need to create a specific animation using Motion Flow Mode.
Motion Flow Mode: Cutting animation together is a fast way to create the animation you want. For example, you can splice just the stretch motion in one file into the walk motion of another file. If two characters are interacting, load both characters into your scene, then perform Motion Flow editing on one character while the other character's motion is visible in the viewports.
To save your script motion into one long .bip file, use Create Unified Motion in the motion flow script rollout. When you leave Motion Flow mode you will see the keys for the whole animation, now as one single sequence. Or use Save Segment to generate a single long .bip file and save it in a single step.
Footstep Creation: To generate a motion, select Footstep mode and use controls on the Footstep Creation rollout to quickly generate a walk, run, or jump pattern. These motions typically need editing to produce more than a generic motion. However, they will provide a good starting point when creating a new animation. For example, to create your own running motion, generate a default run in Footstep mode. Then use Set Multiple Keys, on the Keyframing rollout, in conjunction with Track View to create or manipulate keys that will adjust the motion to your liking. Track View in conjunction with Set Multiple Keys is used when many keys need to be adjusted simultaneously.
Layers: You can use the layers rollout to make adjustments to your animation. Create a new layer and make any freeform changes you like to your existing biped animation. This is non-destructive, you can always turn off the layer to return to the earlier animation. This is very useful for experimentation when you're not sure what direction you want to take. Layer animation can be collapsed into a single layer when you want to commit to it. Layers let you build infinite variety from one set of motion capture; you can add secondary motion without losing your base animation.