So the Pinewood Derby is around the corner and you want to make the coolest car for the race. You realize that you don't want to make your car out of wood and the pre-cut wood templates look tacky. Then you realize that you can make your car using a 3D modeling program and get it printed on a 3D printer! How does one do this? Well, I will show you how you can make a Bob-omb car (which is the coolest car) so you can have something awesome racing down the track at the Derby!

P.S. This is my first instructable so please be gentle and give me some feedback so I can improve on any future instructables that I make.

Step 1: Research (know the Rules)

Before you start creating the car, you need to know the Rules! Most pinewood derbies will have certain rules that one must follow to compete in the race. You can find those basic rules at this website: http://www.pinewoodpro.com/pinewood-derby-cars-rules.htm

For this particular car that I made there were extra rules that I (and others) had to follow. For example: "Cars shall contain an accessible, closeable compartment for adding or removing weight. No external weights, and no weight that is taped, glued, or otherwise “stuck” on the car is allowed. No tools should be required to add or remove weight."

You will also need to know what the size of the wheels/axles and possibly the size of the track so you can design the car so the wheels/axles can fit to the car and the track. Lucky for you, I will provide some of that information to you in these pictures.

Step 2: 3D Modeling

WARNING: This step will only make sense IF you know how to use any 3D modeling program (ex: Autodesk Inventor, Solidworks, ProE). I used Solidworks to create this car. If you don't know any basics about 3D modeling then I would recommend Youtube. (Sorry, I would basically be writing a novel if I described every feature that I used to create this car)

In this step, I will give you the basic features that will help you create the Bob-omb car:
-revolve
-cut extrude
-shell (see next step for reason why I used this feature)
-boss-extrude
-dome
-mirror
-circular array
-fillet
-sweep
-cut-sweep
-cut-revolve

(Note: The picture provided is a reference that will help you visualize what you are making)

Step 3: 3D Printing

You finished modeling the coolest car for the pinewood derby. Now you need to make that model into a physical part. This step will cost you money (unless if you have a friend or a friend-of-a-friend that will let you use their 3D printer for free or a bribe). There are websites that will create this for you and ship it to your door (which is VERY expensive). Another way would be to find a school/college that has a 3D printer that you can use as well(which I did and its cheaper). Either way, they will charge you depending on the material and the volume of the model.

Some of the credentials that they need to print are:
-type of file (ex: DAE, OBJ, STL, X3D, X3DB, X3DV, WRL) I used .STL
-Units it was made. (inches or centimeters)
-Material to use. (I used ABS Plastic.)

Note: you can model the car as one Whole part or in separate parts and then put them together. Word of caution: The less material you model, the cheaper the price to print. (this is why I used the shell feature to remove most of the material.)

Step 4: Final Touches (painting)

Now you have your creation! Now its ready to paint.

Things to consider:

-know what kind of paint you are using before applying on the 3D part. I used acrylic paints.(ABS plastic + aerosol spray paint = melted ABS plastic and a very upset person). Not sure if the paint is going to work or if it looks good? Then test a small area on the car that is hidden from plain site(like the bottom of the car.) then you can judge on what kind/color of paint is best to use.

-Sanding the car before painting: I'll admit, I didn't sand my car before I painted. The reason why is because I was using acrylic paints and acrylic paints needs a rough surface for the paint to stick. If you look closely at the picture, you can see "lines" on the car and it looks rough. If you want your car to look really smooth and nice then sand the whole car or put a lot of layers of paint.

Step 5: Ready to Race

Now your done! You can now hold your creation in your hands and feel the power of the Bob-omb car. (Just kidding, but seriously, its an awesome feeling to make something from a computer to a physical thing!)

Just remember:
-use graphite before the race. It make a big difference when you go down the track. Trust me.
-read the rules again. Its always fun until you are disqualified because of a simple rule that you overlooked.
-Have fun! Its the journey, not the destination, that matters!