Footstep and Freeform modes both use the same underlying inverse kinematics (IK) to animate the biped skeleton. Footstep gizmos are a method for manipulating sequences of IK keys.

With inverse kinematics, you animate a hierarchy, such as a biped’s leg, by animating a lower link in the hierarchy: for example, the biped’s foot. Inverse kinematics is the opposite of forward kinematics. Forward kinematics doesn’t use the hierarchy; for example, you might animate a leg by rotating the thigh.

In this lesson, you’ll learn how changing the IK keys affects the footsteps.

Set up this lesson:

• Open footsteps_keys_start.max.

  A biped is displayed with four footsteps in the viewport.

  

Set IK Keys to create footsteps:

1. Scrub the time slider to play the animation.

   The biped hops on his right foot. Notice that there is no footstep for the right foot between footsteps 2 and 3.

   

2. At frame 45, select Bip01 R Foot.
3. On the Motion Panel Key Info rollout, click (Set Planted Key).

   The pivot point is displayed in the viewport. If you can't see it, change to Wireframe viewport shading, or navigate the viewport so you can see beneath the heel.

   

4. On the 3ds Max status bar, turn on (Key Mode Toggle).
5. Click Next Key to go to frame 48, and then click (Set Planted Key).

   The pivot point shifts to the toe.

   

   Note that the lowest IK pivot is selected by default for cases where IK is applied to new keys.

6. At frame 54, click (Set Planted Key).

   

   The biped is moved back to the ground. A footstep is displayed beneath the biped’s foot.

   A footstep has been created, because there is now an interval of time where IK is applied between the two planted IK keys. However, if you drag the time slider to play the animation, you will see that the walk still needs work.

Change the duration of footsteps using IK keys:

1. At frame 60, click (Set Planted Key).
2. Play the animation now. The walk cycle is much better.
3. Right-click the foot and choose Dope Sheet.
4. On the Dope Sheet tool bar, turn on (Edit Keys) if it is not on already.
5. On the Biped rollout, turn on (Footstep Mode) to easily locate the track in Dope Sheet.
6. Expand the Bip01 Footsteps Transform track. Notice that footstep 3 extends for 15 frames, from frames 45 to frame 60.
7. Turn off Footstep Mode.
8. Select Bip01 R Foot once more.

   The keys for the foot are displayed in the Dope Sheet

9. At frame 63, set another planted key.
10. Turn on (Footstep Mode).

    The Dope Sheet editor again displays the Footsteps track.

    The duration of the footstep now is 18 frames, from frames 45 to 63.

    

11. Turn off (Footstep Mode).
12. Close the Track View - Dope Sheet window.

Remove footsteps using IK keys:

By editing IK keys, you can remove footsteps as well as add them.

1. At frame 45, select the Bip01 R Foot object in the viewport, then set a free key.
2. At frame 48, set a free key.
3. At frame 54, set a free key.
   NoteThe body vertical position is modified. The biped now floats up into the air at frame 54.
4. At frame 60, set a free key.

   The footstep disappears.

   There is only one IK key left. With no IK interval defined, there is no duration, and therefore no footstep. The result is that the biped hops between footsteps 2 and 3.

   The animation could be made more realistic by adding arm movement to the hopping steps, or by creating a freeform period for the hop, then adding poses for a crouch, spring and landing. The point of this lesson, however, has been to demonstrate that footsteps can actually be created or removed by changing the IK keys.