Ok so far the I have 2 objects, one a passive RB, one a active RB that has an expression on its impulse to make it move in the Z direction. Below is an expression that makes there colour change when getting with in a certain proximity of each other... //get objects translates vector $obj1=`getAttr obj1.translate`; vector $obj2=`getAttr obj2.translate`; //subtract one from other float $mag = mag($obj2-$obj1); //change colour when within certain proximity if ($mag <= 10) setAttr lambert1.color 1 .5 .5; else setAttr lambert1.color .5 .5 1; This is showing it recognises the proximity, now how would I go about making the active RB go round the passive RB? Thanks Chris