If you have the courage to open up old electronics and scrounge for parts, you can build a solar-powered toy entirely from recycled home materials. For instance, small DC motors may be found in old appliances with spinning parts, such as VCRs or computer fans. Old CDs or spools can serve as wheels attached to car bodies constructed from disposable containers. Finally, solar panels pulled from old garden path lights can provide the power for your device. Since the materials at hand will vary, many different models can be constructed working from the same basic plan.
Lay your light cardboard or plastic container on its side so that it is long and low like a car.
Measure and mark the side of the container a couple of inches back from the front and a couple of inches up from the bottom of the front end. You will insert the front axle here. Measure the width of the container at this point to help determine the front axle length.
Measure and mark the side of the container a couple of inches forward from the rear and a couple of inches up from the bottom of the back end. You will insert the rear axle here.
Cut a hole in the top of the container so you can reach inside to mount the motor and run wires.
Cut two axles from the rods. The front axle should be long enough to hold two wheels on either end without rubbing the sides of the chassis. The rear axle should be longer, with room to accommodate a rubber band as a drive-belt.
Fit a wheel onto the end of the short front axle, securing it with a rubber grommet or hot glue. The wheel and axle should turn together as a unit.
Punch two round holes across from each other on the sides of the chassis near the front bottom, at your mark. The axle will slide through these holes and will need enough clearance to spin freely.
Cut four short (approximately .75 inches long, but will vary depending on the scale of your car) pieces of tubing to serve as spacers to keep your wheels from rubbing on the chassis.
Slide a spacer onto the front axle until it rests against the attached wheel. Mount the front axle onto the chassis through the holes, then slip on another spacer and the second wheel.
Test the alignment of your wheels before you permanently secure the second wheel to the axle. The two wheels should be parallel, not toeing in or leaning out from each other.
Repeat steps 2-6 for the rear axle, except punch the holes through the sides of the chassis near the rear bottom. Also, before attaching the last spacer and wheel, slip the rubber band onto the axle between the sides of the chassis. The rubber band will serve as a drive belt or pulley.
Paint the wheel edges with the puffy paint and let dry, to add traction. You can also use rubber bands for this purpose.
Mount the Drivetrain
Fit the drive belt over the motor and position the motor so that the pulley is taut but not stretched too tight. You may need to prop it up with pieces of cardboard or hot glue. Turning the belt should turn the rear axle.
Secure the motor to the chassis of the car using hot glue or plastic ties. It should not shift, even if the car crashes.
Mount the solar panel on the top of the chassis, using the plastic ties or rubber bands.
Connect the positive lead of the solar panel to the positive terminal of the motor using the wire. Complete the circuit by connecting the negative ends of the panel and the motor, using a second piece of wire. If the leads are connected correctly, the car will run forward. If it runs backwards, switch the leads.
Take your solar toy car out into the sunlight to test how it functions.
Sand the axles lightly to give your drive belt more traction. Wind tape around the axle where it meets the drive belt to change how many times the axle turns per spin of the motor. Experiment with the tilt of the solar panel, shape and weight of the chassis, and wheel and axle diameters to adjust your car speed.