The string length is determined by the location of the eye in relation to the door being closed (longest length). A knot is tied (at a measured spot) to stop the ball at the correct height of the windshield-and the slack hangs loosely.
Its a cool, easy, quick and cheap project.
Step 1: Tools and Materials
-Ladder (or stool)
-3/32" bit (used to drill pilot for Eye)
-3/16" bit (used to drill hole in tennis ball)
-Needle nose pliers
-20 feet of paracord (length depends on your garage)
-Fishing sinkers (or similar weight such as screws/sand/etc.)
-Hook and Eye (only Eye used-inside diameter of 1/4 inch)
An automatic garage door opener is obviously needed for this~