This project gives some familiarity with electricity, motors and wiring. It also gets a child thinking about drive methods, gears/pulleys and their ratios, since the wheels are obviously turning much slower than the motor, power to the wheels being geared down in two stages. Another principle is that of friction and how rubber around the wheels results in more traction. All of these principles can be raised for discussion and further investigation if it seems appropriate for the student’s level.
The car evolved out of many attempts to make a simple wooden electric car. The only “high-tech” parts are the motor, battery holder and a curtain pulley, all of which I found down at the local D.I.Y. store. You also need some rubber bands, a 5″ nail, some screws and washers and suitable plastic bottle caps for the wheels. For added traction we cut eight pieces from an old bicycle inner tube and put them around the wheels.
The rubber bands for driving the wheels are easy to get, and are also arranged to be easily replaced. You don’t need to disassemble anything when they wear out. This was particularly important as a design consideration in Taiwan, as the humidity makes them deteriorate pretty fast.
The following picture is the first design that actually worked, but it had some shortcomings. It lacked traction and the pulley often got stuck on things because it was lower and turning in the opposite direction to the wheels.
The final design worked much better, however it was necessary to add smaller rubber bands from the drive shaft to each wheel.
To make it, start with the wooden base. A little bit of drilling is required which is best done by an adult. It should look like this with the wooden axles glued and nailed on:
and viewed from the top:
(If you want to paint it, it would be easiest to do it now.)
Next, the motor is mounted using a suitable sized metal bracket (also from the DIY shop.)
Then the battery holder, and the wires can be soldered to the motor (which way will have to be found by trial and error. If it goes backwards, reverse the wires!)
The drive shaft assembly looks like this, with the curtain pulley glued on with a two part epoxy glue.
and when assembled, the drive shaft should look like this (note that this picture is for illustration only. An actual car in progress should have the wires connected to the motor by now and the battery holder nailed on):
Next, this might be a good time to add the seat and windshield. It’s not important how you make the seat. This one was made from two pieces of wood glued together and had a nut underneath to keep it above the motor mounting bracket.
The windshield was made from a piece of plastic-coated wire, such as some coat hangers are made of. Drill a couple of small holes to push it into.
Then we should be ready to screw on the wheels. Note that each wheel is made from two of these milk bottle tops back to back. Also, it was found necessary to wire them together as you can see in the photo, drilling six holes around the circumference and threading the wire around. Two strips of bicycle tube were stretched around each one:
Then after putting on the rubber bands, a small one from the motor to the drive shaft, four small ones from the drive shaft to each wheel, then the two bigger ones around each pair of wheels (these allow it to climb over things a lot better.)
All being well, it should work. Here is a video of the first prototype: