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Reaction Controllers 343
4.
Go to the Motion panel, and on the
Assign Controller rollout, click the Position
track to highlig ht it.
5. On the Assign Controller rollout, click the
Assign Controller button.
6. On the Assign Position Controller dialog, click
P osition Reaction to highlight it, and then click
OK.
This opens the Reaction Manager dialog (page
2–345)
. The Reactions list shows that the
sphere is assigned as a slave, but no master is
assigned. A Reaction controller uses a master’s
motion to control any number of slaves.
7. Right-click the “Unassigned” line at the top
of the Reactions list. From the menu, choose
Replace Master.
This places you in a Pick mode where you can
choose a motion track from any object in the
scene to act as master.
8. In any viewport, click the box (Box01).
Apop-upmenuappears.
9. From the pop-up menu, choose Transform >
Position > X Position.
The “Unassigned” text is replaced by a master
track labeled “Box01 / X Posit ion”.
Also,anewstate,State01,appearsintheStates
list.
This is an example of the basis o f the control
mechanism used by the React ion controller:
For each master/slave combination, y ou can
specify any number of states defined by values
for the master and s lave tracks. T he first state,
created autom atically when you added the
master, specifies that when the box is at -100 on
the X axis, the sphere should be at (-100,0,50).
In this case, you’re controlling three parameters
(the sphere position on all three axes) with one
(the b ox posit ion on the X ax is). More typically
you’d use one-to-one master/slave-parameter
ratios.
Note: Reaction Manager also defines a state
automatically when you assign a new slave to a
master.
Next y ou’ll create a second state that tells the
sphere how to move on multiple axes as the box
moves on one.
10. Movethetimeslidertoframe50.
The box moves to the midpoint of its animated
trajectory. The sphere remains where it is.
11. On the Reaction Manager dialog , click the
Create State button.
This creates a new state (State02) using the
current positions of the box and sphere.
12. Try moving the sphere in the Front viewp ort.
You can’t move the sphere because it’s under the
full control of its master, the box. Similarly, you
can’t change its position using the C oordinate
Display fields on the status bar. However, you