1. Take one of the wheels and one of the steel rods. Place the wheel down on the work surface. Place the steel rod into the hole of the wheel. Tap the steel rod into place. Place washer on steel rod and move it down to the wheel.
2. Measure and cut the straw so that it fits on the steel rod between the wheels when they are both on the rod. The straw length depends upon the inside length of the wheel length where the rod is inserted. Cut the straw to fit this length. The straw should turn freely when both wheels are on both ends of the steel rod.
3. Place the cut length of straw onto the steel rod. Place a second washer onto the steel rod. Put a wheel on the open end of the steel rod and tap into place.
4. Take one of the wheels and the other steel rod. Place the wheel down on the work surface. Place the steel rod into the hole of the wheel. Tap the steel rod into place. Place washer onto steel rod and move it down to the wheel.
5. Measure and cut a second length of straw but this time leave space for a gear which will be placed on the rod before the second wheel. Place cut straw on steel rod. Place washer on steel rod. Place gear on steel rod and tap gear into place. Place wheel on steel rod and tap into place.
6. Use the hot glue gun and place a line of glue along the length of the straw. Carefully place the balsa on to glue ½ inch from its end. Repeat with the other axle.
7. Attach the smaller gear to the motor to form a gear/motor assembly. Place the gear/motor assembly so that the teeth of the small gear line up with the teeth of the larger gear. Move the assembly out of the way enough to place a line of hot glue on the balsa wood. Set the assembly on the glue line.
8. Glue the underside of the solar cell to the top the balsa wood.
9. Connect the wires of the solar cell and the motor.