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 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 AC motors DC motors DC servo motors DC 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.

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.

DC Electric Motors DC Electric Motors use Direct Current (DC) sources of electricity: Batteries

DC Electric Motors DC Electric Motors use Direct Current (DC) sources of electricity: 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

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) 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) 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)

+ 6 V –

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