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~
Step 2: Prep
Drill a 3/16" hole into the tennis ball.
Insert about 2 ounces of fishing sinkers/old screws/sand/ anything that will fit inside the hole (helps lower the tennis ball).
Tie a figure eight knot at the end of the paracord and shove into the tennis ball.
Step 3: Eye Location
Grab the marker and tennis ball/cord combo
Using the ladder/stool, find the ideal location for the parking aid. I centered the ball on the steering wheel for the X axis, and centered up and down on the windshield for the Y axis. This way- I center the aim the ball center line with my steering wheel.
Mark the location on the ceiling/joist-this is where the eye will be installed.
*Optional-move the car out if you don't want wood shavings dropped on your car-or a cordless drill going through the windshield*
Drill a 3/32" hole in the marked location and install the eye.
Step 4: Making It Work
Move the car back in if you previously moved it out.
Adjust the ball to its ideal height (centered on windshield) and tie a figure 8 knot on the side towards the garage door opener bracket so the ball will not drop further than the specified height.
Position the eye so its "looking" at the middle of the track.
Close the garage door.
Route the cord from the eye to the bracket so it wont interfere with anything.
Insert the loose end through the garage door opener bracket.
Pull the slack so the ball is in the stowed position (up out of the way). Leave enough slack on the ball (about a foot or so from the Eye).
Loosely secure the cord to the bracket and open and close the door a couple times and adjust height and stopper knot as necessary.
When happy with location/height-trim the loose end and secure the knot.