PASCO SE-8657 MOTOR ACCESSORY - Manual (Page 13)

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012-06247A Motor Accessory
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Procedure—Part A
➀
Rotate the armature and observe how the segments of the split ring commutator contact the
brushes as the armature turns.
➁
Remove the armature from the shaft by grasping it between your thumb and forefinger and
rotating it back and forth while lifting gently. If necessary, insert a pencil between the
brushes to gently separate them to remove the armature.
➂ Examine the armature closely and imagine current entering one of the split rings from a
brush. Trace the path of the current through the wire to the coil, through the coil, through
the wire to the coil on the opposite side of the armature, through that coil, and through the
wire to the other split ring and into the second brush. By carefully examining the part of
the coils where the wire emerges from the coil, you can determine the direction in which
the wire is wound on the coil (see Figure 3).
➃
Holding the armature in one hand, imagine that the brush from the + lead is touching one
of the split rings of the commutator. Follow the wire from the split ring to the right coil of
the armature and note the direction the wire is wound in the coil. Note where the wire
enters the coil and where it exits.
➄
Use the right-hand rule to determine the direction the magnetic field will flow when you
turn on the power: Grasp the coil with your fingers wrapped around the coil in the direc-
tion of the current (Figure 4). (Current direction is described by convention as being from
the positive to the negative lead. Note that this is opposite of the direction of electron
movement—see note on page 10) . Your thumb will point in the direction of the field —
that is, toward the north pole of the coil). Put a small piece of tape on the end of the
armature that will be its north pole when you turn on the power.
➅
Follow the wire over to the left coil. Use the right hand rule to find the direction of the
north pole.
Record your observations on Figure 4.
a) In this situation, is the direction of the north pole the same for the right and left coils?
Figure 3. Direction of the Wire Winding on the Coil