The ordinary motors we see every day -- properly called rotary motors -- consist of a fixed outer part called a stator and a movable inner part called a rotor. A linear motor is a rotary motor with the stator unrolled into a straight line. Instead of rotating, the "rotor" now runs along the stator. It is more logical to think of a linear motor as a vehicle running along a track -- this is how a linear motor usually operates. Linear motors drive trains, monorails and amusement park vehicles.
- Skill level:
Things you need
- Moving Rotor
Replace the stator with a wooden or plastic track -- something for the vehicle to run along. Underneath the track is a series of magnets. The magnets alternate -- one has the North pole facing up, and the next has the South pole facing up, and so on. The vehicle travels along the track because the electromagnet in the vehicle reverses polarity at the right times. The magnet behind the vehicle pushes it, because it repels the similar pole of the vehicle's electromagnet. The magnet in front of the vehicle pulls it, because it attracts the opposite pole from the vehicle's electromagnet. The electricity that powers the vehicle's electromagnet is delivered through the track. The wires along the track drop down between each magnet so the polarity of the electromagnet changes at exactly the point where the electromagnet on the vehicle is over a magnet. The magnet that was attracting now repels and vice versa.
Replace the rotor with a "vehicle" that has an electromagnet. This vehicle moves along the track driven by the power of magnets. Two wires run along the two tracks, crossing over between each of the magnets underneath the track. A battery is attached to the two wires at one end of the track. If the vehicle is not on the track there is no circuit. If the vehicle is on the track the electricity flows through the vehicle's electromagnet. This is how a DC linear motor works -- AC linear motors can use the alternating poles caused by alternating current to eliminate the crossing over of wires.
Test the linear motor and adjust the magnets and wires to tune for maximum performance. You can adjust the distance between the stationary magnets, and you can adjust the clearance between the stationary magnets and the electromagnet. The proper distance in both cases depends on your particular linear motor.
Tips and warnings
- Be prepared that the vehicle will run off the track. There should be a length of track that exceeds the wires, and has no magnets underneath the track. A wall with some cushioning should stop the vehicle.
- Repeated sliding of the vehicle along the wires will wear on both and also change the clearance between the magnets and the electromagnet. This friction can be reduced by putting wheels on the vehicle -- although it might be difficult to find wheels that conduct electricity with little loss.
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