I wanted to hang a ball from the garage ceiling without having to have a ladder next to the car.
So I used a guide string and a tennis ball with a ridiculous amount of string attached to the ball to pre-position the ball before mounting a screw eye to hang the ball from.
The theory of operation is that I could use a guide string with the ball tossed over the string to create a sort of triangle. I could then move the point at which the ball was hanging over the string left and right, forwards and backwards. This let me position the ball directly over the point I wanted the ball to touch the car's windshield. I could use the excess string attached to the ball to move the ball up and down to be sure that it actually touched the car where I wanted it.
I set up the string with the car outside of the garage, thus lowering the risk of me scratching the car with the ladder. I manipulated the jig while the car was in the garage, which allowed me to accurately hang the ball.
The downside was that I had to move the car in and out of the garage about 3 times.
Step 1: Step 1: Hang the String!
For this step, you are going to want a few things:
2) Small screw eyes that won't fall out of the ceiling while in use but also won't leave much a hole behind.
3) Tennis ball with string already ran through it. I had about 10 ft of string attached to my ball when I got started.
4) String to run through the eyelets.
Steps to complete this step:
1) Get an idea of where the guide string is going to go. You'll want it behind the point the ball will rest against the windshield - otherwise you won't be able to get the ball in position. Do this by getting the car where you want it and make a mental note of the position 3-4 feet behind that spot. Once you have that spot, you can move the car back out of the garage.
2) Screw the screw eyes into the ceiling a few feet back from the general area the ball is going to be hanging from.
3) Run string through both eyes (you can't have too much slack). Tie the string off at one end and anchor it at the other. You'll be releasing/pulling in wire on this end, so I would find something with a small radius to wrap the string around. The smaller the radius is, the smaller your adjustments will be. This will let you fine-tune the position of the ball.
4. Pass the ball over the guide string and anchor the other end of the ball somewhere forward of where the car is parked. You will be using this to adjust how far the ball hangs from the ceiling.
Now you have 3 directions you can moved the ball:
1) Up and down using the string the ball is connected to.
2) Forwards and backwards by releasing/pulling in the guide string.
3) Left and right by sliding the ball left and right above the guide string.
Step 2: Adjust the Strings Until the Ball Is in the Optimal Spot
1) Move the car back into the garage. This is when you want to be sure the car is right where you want it.
2) Lower the ball until it is touching the windshield.
3) Move the ball left/right until it is aligned with the target position along this axis.
4) Pull in/release the guide string until the ball has moved back/forward enough to align with the target position along this axis.
5) Repeat these steps until you have the ball right where you want it.
Step 3: Replace Guide String With Screw Eye
1) Now that we have the ball in place, pull the car back out of the garage and grab the ladder.
2) Put a piece of scotch tape above the point the ball and guide strings intersect.
3) Use a level as a straight edge to mark the intersection point as best as we can. Mark one line while you hold the level against (while trying not to push) the ball string. Mark the other while you hold the level against (again, while trying not to push) the guide string. You should have a nice little "x" or "+" depending on your viewpoint.
4) Drill a hole with a small drill bit through that intersection on the tape. This does two thing:
a) You can tell if there is stud there. If there isn't, you may want to use a drywall anchor to be sure that you don't inadvertently pull out the screw eye in the future.
b) You can pull down the tape without losing where the screw eye need to go.
5) Screw in the screw eye, using a drywall anchor if necessary.
6) Take down the guide string, the guide string's screw eyes, and the ball string.
7) Run the ball string through the screw eye, re-anchor it.
8) Pull the car back into place into the garage.
9) Reposition the height of the ball, anchor when finished.
10) Pull the car out of the garage.
11) Mark the string as it comes out of the screw eye (see picture if confused).
12) Cut excess ball string (leaving enough to tie a knot at the screw eye.
13) Tie knot at the screw eye, making sure to keep the mark in the string placed correctly.
Step 4: Admire Your Handiwork.
You are an amazing person.