8

Spring Dynamics Object 377
so all of the dynamics parameters w ill be
disabled for the spring object.)
3. Include at least one of the bound objects or
aparent
of one of the bound objects in the
simulation. For example, you can bind the
ends of a spring to two dummy objects, and
oneofthedummiescanbethechildofan
object that’s included in the simulation. The
dummy without a parent wil l b e stationary and
the spring w ill pass its force through the other
dummy to its parent.
Note: Spring is an "ideal" object with no mass.
While it can be used in dynamics simulations,
it cannot participate directly in collisions or
effects. A spring can only exert force on other
objects in simulations. As a result, when you
assign a spring object to a dy namics simulation,
andthenviewitintheEditObjectdialog,allof
the parameter settings are disabled.
Inter face
Spring Parameters rollout
End Point M eth od group
Fr ee S p ring —Choose this when using the spring as
a simple object that’s not bound to other objects or
used in a dynamics simulation.
Bound to Object Pivots—Cho o se this when binding
the spring to two objects, using the buttons
described next.
Binding Objects group
Usethesecontrolstopicktheobjectstowhichthe
spring is bound. "Top" and "Bottom" are arbitrary
descriptors; the two bound objects can have any
positional relationship to each other. To complete
the binding, select two binding objects, and then
click Bound to Object Pivots.
Each end point of the spring is defined by the
center of the overall diameter and the center of the
wire. Thisendpointisplacedatthepivotpoint
of the object to which it is bound. You can adjust
the relative position of the binding object to the
spring by transforming the binding object while
the Affect Object Only button is turned on in the
Hierarchy > Pivot panel.
Top (label)—Displaysthenameofthe"top"binding
object.
Pick Top Object—Click this button and then select
the "top" object.
B ottom (la bel )—Displaysthenameofthe"bottom"
binding object.
Pick B ottom Object—Click this button and then
select the "bottom" object.
Free Spring Parameters group
Height—Use t his field/spinner to set the
straight-line height or length of the spring when it
is not bound. This is not the actual length of the
spring ’s wire.