AGXBreakableJoint

AGXBreakableJoint is a joint using AGX Dynamics that breaks (becomes disabled) when certain conditions are met. The implementation uses Hinge, Prismatic, and LockJoint from AGX Dynamics.

Sample

Let’s explain how to use this with a sample. The sample project is located at: By operating DoubleArm to grasp and pull the door, you can see the hinge constraint disappear and the door come off.

• Project file: chorenoid/sample/AGXDynamics/agxBreakableJoint.cnoid

• Body file: chorenoid/sample/AGXDynamics/agxBreakableJoint.body

Break Conditions

As explained at the beginning, AGXBreakableJoint triggers breaking when certain conditions are met. There are two types of conditions, specified by the breakType parameter.

• When receiving force above a certain level for a certain period of time (breakType: force)

• When the received impulse exceeds a threshold (breakType: impulse)

breakType should be chosen based on how force is applied. For example, in a scene where a hinged door is removed, force is appropriate. On the other hand, for objects that receive periodic impacts from a drill, it’s difficult to continuously receive force above a certain level, so impulse is appropriate.

Syntax

AGXBreakableJoint is written and used as follows:

links:
  -
    name: Door
    parent: PillarL
    jointType: free
    elements:
      -
        type: AGXBreakableJointDevice
        link1Name: PillarL
        link2Name: Door
        jointType: revolute
        jointRange: [ 0, 180 ]
        position: [ 0, 0, 0 ]
        jointAxis: [ 0, 0, 1 ]
        jointCompliance: 1e-6
        breakType: force
        period: 3.0                 # For 3 seconds or more
        breakLimitForce: 3000       # Apply force of 3000N or more
        validAxis: [0, 1, 0]        # In Y-axis direction to break

1. Set the links to connect with AGXBreakableJoint in linkName

2. Set the joint type in jointType

3. Set the joint position and axis in position and jointAxis

4. Set the break type in breakType

• For breakType: force, set breakLimitForce and period

• For breakType: impulse, set breakLimitImpulse

5. Optionally set spring stiffness and damping in jointCompliance and jointSpookDamping

6. Optionally set validAxis. validAxis can specify which axes of the joint to use for breakLimit calculation. For example, in the figure below, setting validAxis to [0, 1, 0] means that forces applied in the XZ-axis directions are not considered.

Parameter Descriptions

The following describes the parameters.

Parameter	Default Value	Unit	Type	Description
type: AGXBreakableJointDevice	-	-	string	Declaration to use AGXBreakableJoint
link1Name	-	-	string	Link name
link2Name	-	-	string	Link name
jointType	-	-	string	Joint type: revolute, prismatic, fixed
position	[ 0, 0, 0]	m	Vec3	Joint position as seen from link1 coordinate system
jointAxis	[ 0, 0, 1]	-	Unit Vec3	Joint axis
jointRange	[ -inf, inf ]	m or deg	Vec2	Joint motion range
jointCompliance	1e-8	m/N	double	Joint compliance
jointSpookDamping	0.33	s	double	Joint spook damper
breakType	force	-	string	Break type: force, impulse
breakLimitForce	double_max	N	double	Force threshold for joint breaking
period	0	s	double	Time threshold
breakLimitImpulse	double_max	Ns	double	Impulse threshold for joint breaking
offsetForce	0	N	double	Offset force
validAxis	[ 1, 1, 1 ]	-	3-element sequence	Specifies which directions of X, Y, Z axes to enable. Setting 1 for a component enables force monitoring in that axis direction
signedAxis	[ 0, 0, 0 ]	-	3-element sequence	Sets the sign of force threshold for X, Y, Z axes. 0 means both ±, 1 means positive only, -1 means negative direction only