This instructable will explain to you the steps needed to bring an almost-fully custom pull-back car to life, using tools such as a laser cutter and CAD software.

The required materials to build a car similar to the one in this tutorial are about-
-One 12x12in sheet of acrylic.
-One pencil
-One rubber band.
-Recommended: Rubber material to put onto wheels for traction.

Tools used-
-Full Spectrum laser cutter
-Solidworks 2012
-Tape
-Round file

Step 1: Design Philosophy

The function of a rubber-band powered car is to be propelled forward by the elastic force provided by a rubber band when the car is pulled back. The mechanics of this are simple. You affix one side of the rubber band to the back axle(using tape, glue, bolt, or etc.). The other end of the stretched rubber band is placed on the front wall in a way that it can be pulled on but will not come off.

When you pull the car backwards, the rubber band is forcefully pulled around the axle by the torque that you indirectly applied to the wheels. This stores elastic energy in the rubber band. So when you release the car, the rubber band will quickly unwrap itself, applying torque to the back axle, sending the car forward.

Step 2: CAD Tips

When you first start designing your car, make sure you know all of the features it will need.

1. First and foremost, you will need a way to bind together your chassis. I used small ridges on the sides that insert into slots on the other pieces. These were glued together, but you can use another, more stable way that involves bolts and nuts. Make sure your dimensions are precise, or you will end up having to do a lot of filing, or worse, redo the parts entirely.

2. Next you will need the side pieces that go above the wheels and help hold the car together. Create circles for the wheel channels, and use lines to extend them upwards, moving the chassis closer to the ground.

3. In between these side pieces, make two parts with holes in them that line up with the wheels. These will hold the pencils used for the axles in place, and also help with overall stability.

4. The wheels in the drawing are meant to be printed out of plastic on a 3D printer, but due to limitations in time, I had to cut out a simple version on the laser.

5. Create a smaller version of the wheel to act as a bracer for the axle.

6. For the back and front pieces that hold the robot together, don't forget to make a slot for the rubber band to mount onto, as shown. Only one of them will hold the rubber band, but this way, it can be reversed if one of the sides break.

Step 3: Construction

Once you have all of your parts cut, you can put the car together. I used super glue and t-slots, but if you are concerned strength, alter your design so that you can construct the car using small bolts and nuts.

After gluing the chassis together, use any means necessary to cut a pencil to the desired lengths, and then insert the pencil pieces into their axle holes.

To fit the wheels and bracers onto the pencil snugly, you will have to make the hole slightly smaller in the design, and slowly file it out, up until it fits perfectly.

Finally you have a rolling car! but now you must attach the rubber band. Place one end in the slot that was designed to constrain it, and stretch the other end of the rubber band towards the opposite axle. Use a piece of tape on the inside to hold the rubber band onto the axle.

Step 4: Complete!

Now that you have your rubber-band powered car, try it out! You may find that the wheels are not very good for maintaining traction. Try to bring the ingenuity out in you to solve problems that I failed to look for! Perhaps glue rubber bands to the edges of the wheels?

Thank you for reading my Instructable. I had fun making this for my Digital Manufacturing class, and I hope some of your have learned from it. :)