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Homework Help: Direction of rotation of a direct current motor

  1. Oct 20, 2016 #1
    1. The problem statement, all variables and given/known data
    I recently made a direct current motor with a battery and a magnet. Is it possible for the coil to move in both directions without changing the current or magnetic field? If so, why might the motor work better in one direction?

    2. Relevant equations
    F= BIL

    3. The attempt at a solution
    As far as I know, the movement depends solely on the direction of the field and the direction of the current. It is not possible for the coil to move in 2 directions. Am i right?
  2. jcsd
  3. Oct 20, 2016 #2
    If the armature has two poles then the motor may not start without spinning the shaft first. Try spinning it in both directions.

    When the armature coils are moving parallel with the lines of magnetic field flux supplied by the permanent magnets, and no EMF is being self-induced in the armature, that's the point at which you want the commutator to reverse the current.

    The magnetic field of the armature will distort the permanent magnet field flux*, and voltage will still be present across the armature terminals even when the armature conductors are moving parallel with field flux because current will try to keep flowing in the armature as the current decreases.

    Armature reaction and self-inductance cause the electrical neutral plane to be offset (retarded) with respect to the geometric neutral plane.

    *This phenomenon is called armature reaction.
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