Electromagnetic Swing

thingiverse

An automatic electromagnetic pendulum swings using magnetic interaction between a coil and a permanent magnet. The pendulum breaks an infrared beam at the bottom of its arc, activating the coil to give it a kick upward. <b>Construction</b> The construction is straightforward. Pieces can press fit together, but a tiny amount of glue won't hurt. The coil should be around 8Ω, depending on gauge wire, which could require hundreds or more turns. <i>Two versions can be made:</i> A simple version that only needs a battery and momentary switch connected to the coil or an automated version. Two 3 mm holes in the vertical slots accommodate the infrared sensor and emitter. <b>Simple Operation</b> The simplest method is to use a battery and momentary push button connected to the coil. This tests human reaction ability as the button must be pressed exactly at the bottom of the arc. When the button is pressed, the coil becomes magnetized, pushing away (flip polarity as needed) the permanent magnet. <b>Automatic Operation</b> The circuit uses a 940 nm infrared LED and accompanying 940 nm infrared phototransistor. The variable resistor can be adjusted to activate the infrared sensor for the particular light level of the room. Since the coil is only activated briefly, the swing can go on for hours. <b>Materials needed for simple model:</b> <ul> <li>3x12 mm neodymium magnet</li> <li>Four AA Batteries or equivalent</li> <li>Magnet Wire (30AWG or higher)</li> <li>Large paperclip used as axel</li> <li>Momentary Switch</li> </ul> <b>Materials needed in addition for automated model:</b> <ul> <li>3 mm 940 nm infrared phototransistor</li> <li>3 mm 940 nm infrared LED</li> <li>Two 1kΩ resistors</li> <li>2.4kΩ or 1kΩ resistor for IR LED</li> <li>10kΩ variable resistor</li> <li>Three 2N2222 NPN transistors</li> <li>10 µF electrolytic capacitor</li> <li>1N4001 diode</li> <li>Any color visible LED light</li> </ul> <b>Explanation of electronic operation</b> <b>Stage A</b> An infrared LED provides a constant source of infrared light for the sensor. <b>Stage B</b> Since light almost always falls on the phototransistor (Q0), it is essentially a "closed switch" feeding a zero voltage signal to the base of the first transistor (Q1). However, when the beam is broken, the phototransistor (Q0) is "an open switch," and the 1kΩ and 10kΩ variable resistor act as a pull-up resistor feeding a high signal to the base of the first transistor (Q1). This means the coil is only activated when the beam is broken. <b>Stage C</b> Transistors Q1 and Q2 act as a darlington pair raising the current to a high enough level to drive the coil. A 10µF capacitor slows the reaction of the sensor slightly, allowing the coil to be triggered after the pendulum breaks the beam at the bottom of the arc. A 1N4001 diode is used as a flyback diode to avoid back voltage spikes to the transistor. <b>Stage D</b> The last stage is not necessary for operation but amplifies the current to indicate the time the coil is activated. <b>Vide-o-gram of the Swing in Action</b> https://youtu.be/pWDZ7vx25PA