Solar panels work by using the sun's energy to knock electrons off atoms in the bottom layer of a silicon sandwich, so that they are free to move up to the top layer, then flow through a wire to do work. Building a solar toy car is an enjoyable way to learn about solar power and engineering. You can purchase an inexpensive mini solar panel and a hobby motor, then build the rest of the car from recycled materials, styling it to taste. Students may be inspired to join in national competitions for the fastest solar toy cars.
Assemble the rear axle by sliding it through the large gear, then sliding a nylon spacer on either end. Complete the assembly by placing a wheel on each end of the axle. The large gear and wheels should fit snugly on the axle, while the spacers should be loose enough for the axle to spin freely.
Assemble the front axle by sliding two nylon spacers on the remaining axle, then placing a wheel on both ends.
Create the car chassis by trimming the box, bottle, or foam core so that it is narrow enough to fit on the axles without rubbing the sides of the wheels. Decide where you will place the axles and mark the point where the large gear will protrude through the chassis.
Cut a slit or notch in the bottom of the car chassis large enough for the large gear to turn without touching the sides.
Hot-glue the nylon spacers of the rear axle to the chassis so that the large gear fits through the slit you cut, and the wheels are equally spaced on either side. Hot-glue the spacers of the front axle assembly to the front bottom of the chassis.
Fit the small spur gear onto the motor shaft and mesh it with the large gear. The side of the box or bottle may need to be cut open to allow access to the gear. Hot-glue the motor into place, supporting it at the right height with blobs of glue and cardboard, so that it does not slip around during collisions.
Run the bare ends of the solar panel leads through the holes of the alligator clips. Bend and twist them with the pliers so that the leads will stay attached to the clips. If the alligator clips only have tabs but no holes, bend the tabs over the lead ends and solder them in place.
Attach the solar panel to the chassis with the rubber bands or Velcro so that it faces upward.
Clip the red lead of the solar panel to the positive terminal of the motor, and the black lead to the negative terminal.
Test the solar car by taking it outside to the sunshine. Experiment with the tilt of the panel and alignment of your wheels to maximise the efficiency of your solar car.
Mini solar panels can be connected in series to increase voltage, or connected in parallel to increase current, as needed by your motor. Glue can be used to keep wheels and large gear from slipping around on the axle. Good sources of gears include old Lego kits, broken VCRs and tape players, and old Spirograph toys.
Serious burns can result from touching hot glue, hot solder, or the tips of glue guns or soldering irons.