Remember that you can add keyframes to any property in Blender using

the same procedure. Place the mouse cursor above a property and

press the I key.

Go to frame 30 and insert keyframes to all of the influences again. In

frame 31, when your arm gets closer to the sphere, change the

influences. Change the influence to zero for the constraint with

"firstEmpty" as a target and one for the "armEmpty" constraint (Figure

7.29).