What are Fulcrum Points

The AutoPhysics tool separates the animation into intervals with and without Fulcrum Points.
The fulcrum area is represented with a green line. This area can change during animation. Walking animation in particular makes a good example:

On intervals where both legs touch the ground the fulcrum area would be big. Then it shrinks and now only encases one foot.

The tool would also move the character to make their Center of Mass closer to the side which has a fulcrum area.

For the intervals where the character has no fulcrum points, the tool automatically generates ballistic.

If you don’t see green areas around fulcrum points, you should check if the visualization for fulcrum areas is enabled. To do this, click the View Mode selector with the Right Mouse Button and enable the AutoPhysics Areas option on the Visible panel.

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Exercise #1: Animation with constant fulcrum points

To get a better understanding of how intervals with and without fulcrum points work, we can make a simple animation:

  • Take the SImple Model from the sample scenes.
  • Set keys on frames 10, 20 and 30.
  • Set interpolation to Bezier clamped.
  • Enable the AutoPhysics assistant.
  • Play the animation.
Currently, both legs act as fulcrum points during the whole animation. The original animation is completely static, but the physical assistant makes a slight squat.

This happens because AutoPhysics tries to move the character a bit down on intervals with big fulcrum areas. Such behavior is in vein with many real-life situations: during walking, for example, the body would move down when both legs are on the ground.

If such a behavior does not fit with your animation, you can disable AutoPhysics on the corresponding interval.

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Exercise #2: Moving fulcrums

Next, we can make a bit of adjustment to the animation from the previous exercise.

  • Go to frame 20.
  • Move the character’s right leg up.
  • Play the animation and see how the physical assistant reacts.
Now, the character has a big fulcrum area on the interval from frame 0 to frame 20. After frame 20, the fulcrum area only applies to one leg. After frame 20 the physical assistant moves the character’s body in the direction of the standing leg. This is necessary for keeping the balance. On frames 0 to 20 the character prepares for this move by squatting and slightly moving in the opposite direction. After frame 20, the character smoothly returns to the original position.

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Exercise #3: Interval with no fulcrums

Take the animation we made in the previous exercise.

  • Go to frame 10 and raise the character’s left leg.
  • Play the animation to see the changes made by the physical assistant.
Now, there are no fulcrum points on the interval from frame 10 to frame 2o. The physical assistant assumes such an interval implies jumping, so it generates a ballistic. Also, before the jump the character squats and leans in the direction of the standing leg: this way the character prepares for jumping. After the jump the character also squats a little, and only then returns to the original position.

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Fulcrum Point Settings

Any point is considered a fulcrum point on a given interval, if it:

  1. Is placed close enough to the ground.
  2. Doesn’t change its position.
However, you can also manually set any point as a fulcrum point regardless of its position, or you can change the parameters that define a point as a fulcrum.
  • Select the points you need.
  • Open the Fulcrum point tab on the Object Properties panel.
  • Turn on the Enforce button to set the point as a fulcrum with its position not taken into account.
  • Turn on the NotFulcrum button so the point won’t be recognized as a fulcrum disregarding its position.
  • Set the value back to Fulcrum so the point will or won’t be considered a fulcrum depending on its position.

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