Transformation constraint question

Question

There are 2 cubes cube A and cube B. And cube B has a transformation constraint. target object is cube A. please see the picture.

cube B needs to move faster than cube A when it moves in positive X location but it needs to move with cube A when it moves in negative X location, but this constraint setting moves cube B at the same speed as cube A. Besides that cube B's default X location is set to X 10 when transformation constraint is active. it needs to be X 0. What should I do to make cube B move differently in negative and positive location?

Answer 1

you can do this with this script:

import bpy
from mathutils import Vector

def changePosition(frame):
    # triggered by a frame change, any code inside here gets run.

    a = bpy.data.objects['Cube A']
    b = bpy.data.objects['Cube B']
    
    fcurve = a.animation_data.action.fcurves

    x = fcurve[0].evaluate(frame-1)
    x1 = fcurve[0].evaluate(frame)
  
    deltaX = x1 - x
    
    if deltaX > 0:
        b.location = b.location + Vector((deltaX * 2,0,0))
    if deltaX < 0:
        b.location = b.location + Vector((deltaX,0,0))
    
    print("delta is", delta)

    return 0.0

bpy.app.driver_namespace['changePosition'] = changePosition

def my_handler(scene):
    changePosition(scene.frame_current)

bpy.app.handlers.frame_change_pre.append(my_handler)

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Note: You have to "reset" your cube b after the end of your animation because it won't be resetted automatically.

Basically the script reads the animation information of cube a, checks whether the delta x movement is positive or negative and adds then 2 * x (in case of positive) or x (in case of negative) to cube b x position.

result: