The required materials to build a car similar to the one in this tutorial are about-
-One 12x12in sheet of acrylic.
-One rubber band.
-Recommended: Rubber material to put onto wheels for traction.
-Full Spectrum laser cutter
Step 1: Design philosophy
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
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
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!
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. :)