Setting up MotionBuilder Relation Constraint

Coding
,
1

Hello,

I need to setup twist joints (these are leaf joints) in MB using Relation constraints. I know how to set these up manually but hit a wall when doing so through python. Here is a screen grab from the constraint settings of the manual approach:

image
image2333×339 6.79 KB

Notice I’m using a Vector to numbers and a multiply node.

Note: I can already create a relation constraint through Python (seen belwo) but have problems adding the settings. example of the code below:

def create_relation_constraint(self, objParent, objChild, constraint_name, offset = True):
    """
    
    Description: Creates a relation constraint!
    
    """ 
 
    ##Create "Relation" Constraint 
    for i in range( FBConstraintManager().TypeGetCount() ):
        if "Relation" in FBConstraintManager().TypeGetName(i):
            lMyConstraint = FBConstraintManager().TypeCreateConstraint(i)
         
    #for index, element in enumerate(selected_objects):
    #lMyConstraint.ReferenceAdd (0, objChild)
    #lMyConstraint.ReferenceAdd (1, objParent)
     
    #Snap if user desires
    if offset == True:
        lMyConstraint.Snap()
     
    #weight of the constraint
    lMyConstraint.Weight = 100
     
    ##Activate Constraint
    lMyConstraint.Active = True 
    lMyConstraint.Name = "{0}_Relation".format(constraint_name)
    
    return lMyConstraint # Returns FBConstraintRelation

Example of the following commands would really help:

*How to add Sender and Reciever joints. How do you set these to relative and not global.

*How to add and connect the nodes shown in the diagram.

Any help would be great.

Thanks

2

I’ve managed to solve most of this. Here’s some of the code that does the same as my previous image regarding the nodes and connections:

#Create "Relation" Constraint

constriant_name = "Test_Twist_ConRel"

relation_constraint = FBConstraintRelation(constriant_name)

relation_constraint.Active = True # Turn constraint on!

#Set up driver jnt (it's a box in MB)

src_box = relation_constraint.SetAsSource(scr_jnt)

relation_constraint.SetBoxPosition( src_box, 0, 100 )# Set the box position within the constraint setting graph!

src_box.UseGlobalTransforms = False # makes translation/rotation local "Lcl"

#Set up driven jnt (it's a box in MB)

trgt_box = relation_constraint.ConstrainObject(target_jnt)

relation_constraint.SetBoxPosition( trgt_box, 1200, 100 )

trgt_box.UseGlobalTransforms = False # makes translation/rotation local "Lcl"

# Creates Vector to Number and Multiply (a x b) nodes (these are called boxes)

v2num_box = relation_constraint.CreateFunctionBox("Converters", "Vector to Number") # returns FBBox

relation_constraint.SetBoxPosition( v2num_box, 450, 200 )

num2v_box = relation_constraint.CreateFunctionBox("Converters", "Number to Vector") # returns FBBox

relation_constraint.SetBoxPosition( num2v_box, 800, 200 )

mutilpy_box = relation_constraint.CreateFunctionBox("Number", "Multiply (a x b)")

relation_constraint.SetBoxPosition( mutilpy_box, 600, 100 )

# Connect boxes------------------------------------------------------------------------------

src_box_Out = findAnimationNode( src_box.AnimationNodeOutGet(), "Lcl Rotation" )

v2num_box_In = findAnimationNode( v2num_box.AnimationNodeInGet(), "V" )

FBConnect( src_box_Out, v2num_box_In )# connect src_box (atrribute Lcl Rotation) to v2num_box_In ( attribute V)

v2num_box_Out = findAnimationNode( v2num_box.AnimationNodeOutGet(), "X" )

mutilpy_box_In = findAnimationNode( mutilpy_box.AnimationNodeInGet(), "a" )

FBConnect( v2num_box_Out, mutilpy_box_In )

mutilpy_box_Out = findAnimationNode( mutilpy_box.AnimationNodeOutGet(), "Result" )

num2v_box_In = findAnimationNode( num2v_box.AnimationNodeInGet(), "X" )

FBConnect( mutilpy_box_Out, num2v_box_In )

num2v_box_Out = findAnimationNode( num2v_box.AnimationNodeOutGet(), "Result" )

trgt_box_In = findAnimationNode( trgt_box.AnimationNodeInGet(), "Lcl Rotation" )

FBConnect( num2v_box_Out, trgt_box_In )

My problem is how to set the parameter for b [number] connection. This a float value used within the Multiply box. The following image shows this connection marked in red:

image
image1418×331 7.18 KB

I’ve tried ProperyList within the “Multiply (a x b)” box but can’t find any Parameter that could be it.

mutilpy_box = relation_constraint.CreateFunctionBox("Number", "Multiply (a x b)") 
print(mutilpy_box.PropertyList.Find("Name"))

Any help would be great :slight_smile:

1 Like
3

I managed to solve it!

Here is the code:

#Create "Relation" Constraint 
constriant_name = "Twist_Jnt_ConRelation"
relation_constraint = FBConstraintRelation(constriant_name)
relation_constraint.Active = True # Turn constraint on!```

mutilpy_box = relation_constraint.CreateFunctionBox("Number", "Multiply (a x b)") 

twistoffset = -0.8
inplugs = findAnimationNode(mutilpy_box.AnimationNodeInGet(), "b") # Get "b" connection in node.
inplugs.WriteData([twistoffset]) # Offset
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