PASCO SE-8657 MOTOR ACCESSORY - Manual (Page 19)

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012-06247A Motor Accessory
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➂ Working from above, press the brush holder onto the smooth, enlarged portion of the
shaft. Apply increasingly firm pressure equally to each side of the brush holder while
rotating the brush holder back and forth. If this action loosens the retaining nut, tighten it
more tightly, as described in step 2.
➤ Check to be sure the brush assembly is seated as far down on the shaft as it will
go.
➃ Gently lower the armature onto the shaft with the dual slip-ring commutator down. Care-
fully rotate the armature back and forth to separate the brushes and allow the commutator
to slip down between them. If necessary, insert a pencil or similar object down between
the brushes. Use only the most delicate force to avoid bending the brushes and necessitat-
ing adjustments or repairs.
➄ Adjust the gap of the Variable Gap Magnet so there is approximately 1 mm of clearance
between the flat pole pieces and the armature when it is rotated by hand.
Procedure
Part A: AC Generator
➀
During the first part of this experiment, the dual slip-ring commutator should be down,
between the brushes. If it is not, remove the armature from the shaft by grasping it between
the thumb and forefinger and rotating it back and forth while lifting gently. Sometimes it
may be necessary to insert a pencil between the brushes to gently separate them so that
they don’t prevent removal of the armature.
➁ The cylindrical ceramic magnet may be used to determine the polarity of other magnets.
The painted face of the magnet is its North Pole (north-seeking pole). [You can verify this
by hanging the magnet from a thread and observing that the painted face points toward the
North (toward the earth’s north magnetic pole, located in northern Canada).] Determine the
polarity of the variable gap magnet by holding the ceramic magnet near its rectangular pole
pieces. In the event that both poles of the ceramic magnet attract a pole piece, the stronger
attraction occurs when opposite poles are together. Label the pole pieces N and S using
small strips of tape.
➂
Examine the armature closely, and imagine current entering one of the two slip 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 leads emerge from the coil, it should be possible to determine the
direction in which the wire is wound on the coil. Can you verify that the current maintains
its same direction of rotation as it leaves one coil and enters the other? This means that the
two coils of the armature act as a single coil. Ask for help if you cannot.
➃
Label the end of the armature that connects to the upper slip ring with a small piece of tape.
➄ Gently replace the armature onto the shaft. The dual slip-ring commutator should be
down. Carefully rotating the armature back and forth will often separate the brushes and
allow the commutator to slip down between them. Otherwise, inserting a pencil or similar
object between the brushes to separate them may be necessary. Only the most delicate
force should be used to avoid bending the brushes and necessitating adjustments or repairs.