Kinetic Contraptions Build a Hovercraft, Airboat, and More with a Hobby Motor Curt Gabrielson
Contents Acknowledgments ix Introduction 1 Getting Started 5 Safety 9 Basic Circuitry 11 Mounting the Motor 21 Peripherals 31 Land Machines Three-Wheeler 45 One-Wheeler 48 Two-Wheeler 50 Transmission Car 57 Water Machines Airboat 67 Motorboat 70 Paddlewheeler 73 Air Machines Windtube 79 Plane-on-a-Stick 85 Hovercraft 89 Flying Caterpillar 94 Spinning Machines Fan, Color Spinner, and Top 99 Tornado 103 Snow Globe 107 Spinning Surprise Tree 112 Spinning Pinecone 116 Bizarro Machines Hopper 123 Cable Car 127 Wave Machine 130 Bubble Maker 136 Pump 140 Exploring Motors Demos with Electricity and Magnetism 151 Solenoid and Electromagnet 154 Meter 156 Motor 158 Motor Dissection 162 Homopolar Motor 166 Motor = Generator = Meter 169 Appendix: Supply Sources 173 About the Watsonville Environmental Workshop 175
Basic Circuitry Two main components batteries and motors will make your kinetic contraptions go. To be specific, batteries provide the energy for your machine and the motor provides the force. Electrical energy is stored in a battery. Generally speaking, the bigger a battery is, the more energy it stores. However, there is not a direct connection between the size of a battery and the voltage it gives. For example, AAA, AA, C, and D batteries all give about 1.5 volts. But you can bet your best wire strippers that the D battery will last a lot longer than the AAA in a given circuit. If your contraption must be lightweight, go for the smaller batteries, but understand there s a tradeoff. Rectangular 9-volt batteries are actually six cells of 1.5 volts each rip a dead one apart and see for yourself. (Alkaline batteries contain nastier chemicals then 9-volt batteries, so don t rip alkalines apart.) I ve had bad luck using 9-volt batteries for motors. Such small cells just don t hold enough energy for a motor or other high-current application. Once connected, the battery meets a hasty death. Chemicals within a battery stand ready to carry out two separate reactions: one producing excess electrons, the other consuming them. If you connect those two reactions with a conducting path, the reactions will begin and the electrons will flow from one to the other, making electricity (direct current). A copper wire works well for making the path if you use just copper wire, an enormous gush of current will flow from one end of the battery to the other, and your battery will die within a few minutes. It may also get hot from the chemical reactions happening so fast. The wire will get hot, too, from all the collisions among 11
12 Basic Circuitry those electrons cruising through it. And if the wire is too small or the wrong type, it may even melt or burn up. If, on the other hand, you direct the electricity to flow through the motor on its way from one end of the battery to the other, the motor will turn, producing mechanical force to do work for you. Clever, eh? You can imagine how excited the first people who worked out this little trick must have been. Later in the book you ll learn more about how this trick is pulled off. For now, it s time to explore the nitty-gritty of how to make great contraptions with a motor and a battery. Good Connections: Key to a Well-Functioning Circuit A bad electrical connection won t let the electricity flow freely, so your motor won t be as strong as it could be. It is important for each connection to be solid. Some motors come with wires already connected to them. Others have small ears to which you connect wires. All simple motors have just two places to connect to, called terminals, which is convenient because a battery also has two sides. Connect one terminal to each end of the battery and your motor should spin happily. Try this basic motor circuit. ParTS Electrical tape Knife Motor 2 connection wires 2 brass fasteners 2 paper clips Aluminum foil Nail Batteries Strip a bit of insulation off both ends of each wire. The insulation is made of plastic, which the electricity can t pass through. Attach one wire to each of the motor ears, making sure the exposed copper makes a direct connection with the ear. Be careful not to twist the ears on the motor too much if you break one off, there s only a slight chance that you ll be able to tape or solder it back on.
Basic Circuitry 13 To complete the circuit, you can tape the bare wire tips to opposite ends of the battery, but often that connection won t be good. Brass fasteners make a much better connection, but small tabs of aluminum foil folded over several times will also do the trick. The best way to attach these items onto the ends of a battery to make a strong electrical connection is to exploit the stretchiness of electrical tape. First, smash the brass fasteners flat and affix one to each end of the battery with short pieces of electrical tape. Make sure the points of the fasteners are sticking out above the edge of the battery. Now take a longer piece of tape and wrap it as tightly as you can around the battery, end over end, stretching it hard over each pole so that the brass fasteners are squeezed tightly against the two ends of the battery. Here is the same set up, but with aluminum tabs instead of the brass fasteners.
14 Basic Circuitry Now, twist each stripped end of the two wire leads attached to the motor around a paper clip, so that both of the double ends of the paper clips are free to clip onto something. That something will be the brass fasteners. Be sure the wires are twisted tightly to the paper clips every connection counts. These two paper clips will be used for their intended purpose: clipping onto something thin. Don t hang them loosely over the brass fasteners or the connection won t be any good slide them onto the upright posts. This is not only a good connection system, but also a good simple switch. When the paper clips are both connected, the motor should spin. When one is disconnected, the motor should stop. You may also want to bend one of the brass fasteners around the paper clip at one end so that it doesn t slip off as easily.