PASCO SE-8657 MOTOR ACCESSORY - Manual (Page 27)

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012-06247A Motor Accessory
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a) Does this feel different? How?
b) Explain why.
➄ Repeat with 15 Hz and 6 volts.
a) Does this feel different? How?
b) Explain why.
➤ Troubleshooting: If there was no vibrating sensation in the previous step, the
brushes were not contacting the slip rings, there was no AC voltage present at the
brushes, or some other defect existed. Recheck the connections and gently bend
the brushes inward to make better contact. If neither of these corrects the problem,
get assistance. If there was a vibrating sensation during only part of the rotation,
turn off the power, remove the armature, and examine both the split rings and
brushes for corrosion and pitting. Cleaning these with very fine (600 grit) emery
paper will usually correct the problem and result in better operation.
➅ Turn the power off.
➆
Set up the photogate or stroboscope to measure the speed of rotation of the motor, follow-
ing your teacher’s instructions.
If you are using a photogate, construct a “chopper” of a 3-inch piece of card stock to
interrupt the beam of light from the photogate as follows:
Cut a 3 cm square from corrugated cardboard and punch a hole that is 1 cm in diam-
eter in the center (a #4 cork boring tool works well). If the square slips, you may need
to secure it with tape. Slip the square part way down the split ring commutator so you
can grip the plastic bushing to spin the armature. Position the photogate so the corners
of the square interrupt the photogate’s beam 4 times per revolution.
➤ Notice that the motor is not self-starting. Immediately after you apply the AC
power, start the motor manually by grasping the black plastic bushing at the top of
the armature assembly between thumb and forefinger and spinning the armature. It
may take several attempts to successfully start the motor because you must spin the
armature at a speed that approximately matches the frequency of the power source.
➇ Set the voltage to 8 volts and the frequency of the alternating current to 16 Hz. Start the
motor and use the stroboscope or photogate to determine the rotational speed of the
motor. What is the rotational speed of the armature? If the result is not already expressed
in revolutions per second, convert it to these units.
➈
While the motor is running, lower the voltage to 6 volts. Does the rotational speed of the