Pivot and Rigid Body (New for 5)

Each 3D entity has its own pivot, which is the base for transforming, rotating and scaling. Most of the time you do not necessarily sense the existence of it. However, it influences a lot especially the rotation of a rigid body. To view the location of the pivot of an object, switch to the Move, Rotate or Scale tools and show the gizmo if it is hidden (Shortcut: Ctrl + Q). You may then see the pivot of the object.

The Rotation of a Rigid Body

When a rigid body rotates, the bound of it is in charge of the collision, bouncing and friction. However, the one that is really affected by gravity is the Pivot. It is forced to fall along gravity's direction until the bound is held by another static object.

Friction, collision and bouncing generated by the bound.

Gravity affects the pivot to force the object to fall.

Pivot and Rolling

The position of the pivot affects the rolling behavior of all objects in any shape, especially cylinder and capsules. Because of the inappropriate position of the pivot, the object can appear to never tumble.

  1. Apply a cylinder. Rotate it and set it as Dynamic rigid body.
  2. Play to simulate. You will see that the result is not what you expected.

    The anticipated result.

    The real simulation.

  3. This is because the pivot is at the center of the circle on the dark side of the cylinder; which pulls the cylinder and makes it topple.

    The pivot is pulled by gravity.

    The real simulation.

  4. To fix this, you may simply set the pivot to the center of the cylinder so that it will not stand up.

Creating a Balancing Toy

Although the rotation looks awkward when the pivot is eccentric, you may utilize it to create a balancing toy.

Because the initial pivot is located in the bottom or center of the object, which may cause the object to fall directly.

The pivot is at the center of the object.

The gravity pulls the object by the pivot.

The object falls.

  1. Select the object.
  2. In the Modify panel, click the Edit Pivot button in the Pivot section.
  3. Turn on the gizmo mode and offset the pivot lower than the bottom of the prop.
  4. Assign the prop as a rigid body with Dynamic state. Start the simulation.

    Deflection formed by gravity's direction and the object's blue axis.

    The pivot rectifies the object's orientation and deflection.