Gravity Powered Car

This car moves forward when a sufficiently heavy object is tied to the string.

Hot glue gun, laser printer, 30cmx50cm MDF, 90cm string, sufficiently heavy object

Using a large piece of MDF, laser cut the following pieces

Take the 4 rectangles with holes in them and glue them like shown. These rectangles are called axels. Make sure that the axels line up with the corners of the main body to ensure that the wheels are straight. Apply the glue generously and clean up the excess glue with a tissue paper. Let this sit for 5 minutes to set.

Sand down a 6 mm dowel just slightly so that it can fit into the 3 smallest wheels and allow free spinning. Assemble as shown in the picture. Hot glue the 3 smallest circles, with the smallest one in the centre. Place the spoke through the 2 poles and in the middle place the pulley mechanism

This step is very tricky. You could try to take careful measurements in order to keep the top mechanism straight, however I found that eyeballing it works best. You can rest the 2 long poles on the ground under the main body and make sure that the top part of the spokes are at an equal height. This will ensure that the poles run perpendicular to the body of the mechanism.

Take 2 10mm wooden dowels and fit them through the axles and the wheels. Then mark where the wheel meets the dowel on the outside as shown in the photo above. Measure 1 cm out from the mark, and cut using a wood saw. The dowels may not have cut correctly so you can sand it using a belt sander.

Replace the dowels into the axels and then hot glue the wheels on. Be careful that the hot glue does not attach the dowel to the axel as this will cause the wheel to not spin. Then take a piece of string and hot glue it to the part of the dowel that is exposed by the hole in the frame. Spin the wheels to wrap the string around the dowel, and then thread the string over the pulley mechanism, and you are done.