Transcript 10 - Electric Motors

Electric Motors
What is an Electric Motor?
• Electromechanical device that
converts electrical energy to
mechanical energy
• Mechanical energy used to:
• Rotate pump impeller, fan, blower
• Drive compressors
• Move materials
• Motors makeup for 70% of
electrical loads in industry.
Electric Motor
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An electromagnet is the basis of an
electric motor
An electric motor is all about magnets
and magnetism: A motor uses magnets
to create motion.
Opposites attract and likes repel.
Inside an electric motor, these
attracting and repelling forces create
rotational motion.
A motor is consist of two magnets.
Electric Motor
Motors are powered by a source of
electricity – either AC or DC.
Types of Motors
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AC
DC
DC
DC
motors
motors
servo motors
Stepper motors
Heavy Industrial applications: AC motors
Mobile robotics & hobby robots: DC motor,
DC servo motor, and DC stepper motors
DC Motor Characteristics
When power is applied, DC motors
turn in one direction at a fixed
speed.
 They are optimized to run at a
fixed, usually high RPM.
 Torque is highest at the rated speed
and lowest at low speeds.
 Speed can be varied if a (pulse width
modulation) PWM controller is added.
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DC Motor Characteristics
Almost all can be reversed.
 Inexpensive and commonly available.
 Available in wide range of speeds and
power.
 Suitable for turning, spinning, etc.

DC Motor Characteristics
Not suitable for positioning unless
some kind of position feedback is
added.
 If the applied load is greater than
the capacity of the motor, the motor
will stall and possibly burn out.
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DC Electric Motors
DC Electric Motors use Direct Current
(DC) sources of electricity:
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Batteries
DC Electric Motors
DC Electric Motors use Direct Current
(DC) sources of electricity:
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Batteries
DC Power supply
How DC Motors Work
Electrical current flowing in a loop of
wire will produce a magnetic field
across the loop.
When this loop is surrounded by the
field of another magnet, the loop will
turn, producing a force (called torque)
that results in mechanical motion.
Parts of the Motor
Armature or rotor
Axle (Shaft)
Electromagnets (coiled wires)
Commutator
 Brushes
 Stator (Field Magnets)
 DC power supply of some sort
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Armature
The armature is an electromagnet
made by coiling thin wire around two
or more poles of a metal core.
Electromagnets
Axle
Commutator
Parts of the Motor
Motor Control
Controlling DC Motor Speed
The voltage supplied to a DC motor
controls its speed.
Switch open
Switch closed
Pulse-width modulation (PWM)
• Pulse-width modulation (PWM) is used
to simulate a variable DC supply
voltage.
• PWM is a common technique for
supplying variable power levels to “slow”
electrical devices such as resistive
loads, LEDs, and DC motors
Pulse-width modulation (PWM)
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A pulse-width modulated
signal is a rectangular
waveform with a varying
duty cycle.
A duty cycle is the cycle of
operation of a motor that
operates intermittently
rather than continuously.
Duty cycle is expressed as
a percentage.
Pulse-width modulation (PWM)
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A longer duty cycle means
the voltage is on for longer
and the average voltage
applied to the motor is
higher and vice versa.
A average voltage can be
calculated by finding the
product of the working
voltage and the duty cycle.
Average Voltage ?
𝟓𝑽 × 𝟎 = 𝟎𝑽
𝟓𝑽 × . 𝟐𝟓 = 𝟏. 𝟐𝟓𝑽
𝟓𝑽 × . 𝟓𝟎 = 𝟐. 𝟓𝑽
𝟓𝑽 × . 𝟕𝟓 = 𝟑. 𝟕𝟓𝑽
𝟓𝑽 × 𝟏 = 𝟓𝑽
roboRIO FRC
PWM (outputs)
6V
+
–
END