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730 Chapter 13: reactor
damping values are those greater than or equal to
0.0. The default damping value is 1.0.
Tip: Typically, a Damping value of 1/10th of the
stiffness yields good results.
Act on compress ion—When on, the spring applies
forces to the attached objects w hen its lengt h is less
than its Rest Length. Default=on.
Act on ex tension—When on, the spring applies
forces to the attached objects when its length is
greater than its Rest Length.
Disabled—When on, the spr ing is not used in the
simulation.
Reset Defa ult Values—Click this to set Stiffness,
Rest Length, Damping, Act On Extension, and Act
On Compression to t hei r respective default values.
Linear Dashpot
Create panel > Helpers > reactor > L D ashpot
Menu bar > reactor > Create Object > Linear Dashpot
reactor toolbar > Create Linear Dashpot button
Dashpots t ypically ser ver to cushion impact.
An example of a real-world linear dashpot is
the hydraulic cy linder in an automobile shock
absorber. TheLinearDashpotconstraintlets
you constrain two rigid bodies together in the
simulation, or to constrain one body to a position
in world space. It behaves like a heavily damped
spring with zero rest length. You can specify the
strength and damping, and whether collisions
between the attached bo dies are disabled.
reactor lets you spec ify a dashpot attachment p oint
in each body’s local space. During the simulation,
the dashpot exerts impulses on the attached bodies
in an attempt to make these points match up in
worldspace,thuskeepingthebodiesinthesame
positions relative to each other. The bodies are still
free to rotate around the attachment point.
You do not need to add a Linear Dashpot explicitly
to a simulat ion, as all valid constraints in a
scene are added to the simulation by default. A
two-bodied dashpot is valid if it has two rigid
bodies attached, w hi le a single-bo died dashpot is
valid if it has one rigid body attached. When not
selected, invalid dashpots are colored red in the
view por t.
Procedures
To create a L inea r Dashpot :
• Chooseoneoftheaboveoptions,andthenclick
in any viewport to add the dash pot.
Note: The icon’s position has no effect on the
constraint’s behavior.
To atta ch obj ects to the Linear Dashpot:
1.
Create the Linear Dashpot and the objects to
connect using it.
2. On the linear dashpot’s Prop erties rollout,
click the Child pick button, and then select the
object to use as the child object in one of the
view por ts. By default, this attaches the linear
dashpot to the b ody at the body’s pivot point.
3. If you do not want to assign a second b ody to
the dashpot, turn off the Parent check box, if
necessar y.
4. If the dashpot is two-bodied, repeat step 2,
usingtheParentpickbuttontosetParentfor
the Linear Dashpot.
To create the constra int a nd a ttach objects in a single
step:
•SeetheScripts (page 2–817) topic.
To change the a ttachment positions for the bodies:
1.
With the dashpot selected, open the Modify
panel.