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Chapter 43: Simulating Physics-Based Motion with reactor
FIGURE 43.6
The gizmo icons for each of the reactor objects

Springs and Dashpots
The Spring and Dashpot objects can be linked between a child and parent object. Simply select the Child
button in the Spring Properties rollout, and click the scene object to make the Spring’s child. If no parent is
selected, the Spring is connected between the child object and the Spring object gizmo’s location.
The Align options let you move the Spring to the Child or Parent Body and to use the Child or Parent
Space. Selecting the Each Body option positions the Spring object equally spaced between the child and
parent.
For the Spring object, you can set the Stiffness, Rest Length, and Damping values and whether it acts on
Compression or Extension. The farther the child and parent objects are from the Spring object icon, the
stronger the pull toward the icon, so changing the Rest Length value to a small value causes the two objects
to be pulled quickly together.

Note
The child and parent objects still need to be added to a collection such as the Rigid Body collection to be used in
the simulation. n
Dashpot objects work in a similar manner to Springs. They can be linked to child and parent objects and
include values for Strength and Damping. Linear dashpots force the parent and child objects to maintain
their position as if they were connected by a springy bar. The Angular dashpot forces two objects to retain
the same orientation; rotating one causes the other to rotate the same way.

Plane
A Plane object creates a solid wall that an object cannot penetrate if it belongs to the Rigid Body collection, but
only the face with the normal extending from it is solid. This object can be scaled, and its only property is a
Show Normal option. Also note that this object is not renderable and is not visible in the Preview window.

Motor and Wind
The Motor object can be used to spin objects belonging to the Rigid Body collection in the scene. For these
objects, you can select a Rotation Axis value, as well as Angular Speed and Gain values.

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