Modify the size and location of the Rigid Body Collision Object

Question

Maybe I'm just spoiled by Unity3D, but I would like to reposition and resize the Rigid Body Collision Object of an object in my scene. Is there currently an established method to accomplish this?

In Unity3D, you can adjust the x and y positions as well as the scale of the collision object. Adjusting the collision margin and collision shape do not produce the desired result in Blender 2.78. A thanka you.

*Updated Partially to my Satisfaction: I was able to change the position of the rigid body object relative to the collision object in edit mode which persisted into object mode. However, the ability to scale the collision object remains elusive. It does appear I accomplished one iteration of upscaling though.

Answer 1

You can not resize the collision box itself, but you will notice that if you scale your object your collision box will scale as well. To customize the collision box:

1. Scale your object in Edit Mode to fit the collision box.
2. Note the scale factors on paper and take the inverse of those numbers by calculating 1/x.
3. Then scale your Object by those Factors.

You can also do this with translation by translating in Edit Mode to fit the collision box and doing the inverse in Object Mode

Notice that this will work perfectly for cubes, but if you want spheres you have to keep them spheres. You can not turn spheres into ellipsoids.

Answer 2

You cannot move them. From the Blender manual (emphasis added):

Primitive Shapes

These are best in terms of memory/performance but do not necessarily reflect the actual shape of the object. They are calculated based on the object’s bounding box. The center of gravity is always in the middle for now. Primitive shapes can be shown in the viewport by enabling Bounds in the Object ‣ Display panel.

Use a mesh shape to get more precision:

Mesh-Based Shapes

These are calculated based on the geometry of the object so they are a better representation of the object. The center of gravity for these shapes is the object origin.