2009

The surface used is a "virtual" parametric surface, and not the actual mesh
surface. Objects with a low number of segments might have a mesh surface
quite different than the parametric surface.
The parametric surface ignores Slice and Hemisphere options. So if the object
is sliced, for example, the controlled object will position itself as if the missing
portion were still there.
Since the Surface constraint only works on parametric surfaces, if you apply
a modifier that converts the object to a mesh, the constraint will no longer
work. For example, you can't use it with a cylinder with a bend modifier
applied.
Procedures
Example: To animate a sphere over the surface of a cylinder:
1 In the Top viewport, create a cylinder and a sphere.
2 Select the sphere, open the Motion panel, expand the Assign Controller
rollout, and then expand the Transform heading in the list.
3
In the list window, click the Position item and then click Assign
Controller.
4 In the Assign Position Controller dialog, choose Surface and then click
OK.
The Surface Controller Parameters rollout replaces the Key Info rollout.
5 Click Pick Surface, and then select the cylinder.
6 Turn on Auto Key, and place the time slider at frame 0.
7 Use the V Position spinner to move the sphere to a starting position at
the bottom of the cylinder.
8 Place the time slider at frame 100.
9 Use the V Position spinner to place the sphere at the top of the cylinder.
10 Set U Position to 300.
Turn off Auto Key and play the animation. The sphere moves over the
surface of the cylinder in a helical path.
Surface Constraint | 3295