The common motors, stepper motors, geared motors, and servo motors discussed here refer to DC miniature motors, which are the most common types we encounter in daily life. The subject of motors is quite complex; this article only provides a general overview of the various motors commonly used in robot manufacturing.
An electric motor, commonly known as a "motor," is an electromagnetic device that converts or transmits electrical energy based on the law of electromagnetic induction. It is represented by the letter "M" (formerly "D") in circuit diagrams. Its main function is to generate driving torque, serving as a power source for electrical appliances or various machines.
ordinary DC motor
Ordinary motors are the most common type of motor we encounter daily, found in electric toys, razors, and so on. They typically have only two pins; connecting the positive and negative terminals of a battery to these pins makes them rotate, and vice versa. These motors tend to have excessively high speeds and low torque, and are generally not used directly in toy cars.
When a DC power supply supplies power to the armature winding through brushes, current flows in the same direction through the conductor below the N pole on the armature surface. According to the left-hand rule, this conductor will experience a counterclockwise torque. Current also flows in the same direction through the conductor below the S pole on the armature surface, and similarly, according to the left-hand rule, this conductor will also experience a counterclockwise torque. Thus, the entire armature winding, i.e., the rotor, will rotate counterclockwise, and the input DC electrical energy is converted into mechanical energy output from the rotor shaft. The rotor consists of a stator and a rotor. The stator includes the base, main magnetic poles, commutating poles, and brush assembly; the rotor (armature) includes the armature core, armature winding, commutator, shaft, and fan.
A DC motor is an electric motor that converts direct current electrical energy into mechanical energy. It is widely used in electric drives due to its excellent speed regulation performance. DC motors are classified into three types according to their excitation method: permanent magnet, separately excited, and self-excited. Self-excited motors are further divided into shunt-wound, series-wound, and compound-wound types.
Gear motor
A geared motor is simply a regular motor with a gearbox added, which reduces the speed and increases the torque, giving the regular motor a wider range of applications.
This type of integrated unit, also commonly known as a geared motor, is typically assembled and supplied as a complete set by specialized gearbox manufacturers. Geared motors are widely used in industries such as steel and machinery. The advantages of using geared motors include simplified design and space saving. Following World War II, the rapid development of military electronic equipment spurred the development and production of miniature geared motors and DC geared motors in countries like the United States and the Soviet Union. With the continuous development of the geared motor industry, more and more industries and enterprises are using geared motors, and a number of companies have entered the geared motor industry.
Currently, Germany, France, the UK, the US, China, and South Korea maintain a leading position in the global market for miniature geared motors and DC geared motors. China's miniature geared motor and DC geared motor industry was established in the 1950s, starting with meeting the needs of weaponry and equipment. Through stages of imitation, independent design, research and development, and large-scale manufacturing, it has formed a complete industrial system with increasingly internationalized capabilities, encompassing product development, large-scale production, key components, key materials, specialized manufacturing equipment, and testing instruments.
Gear motors are generally used in intelligent vehicles, and the control of motors usually uses an H-bridge solution. The L298 chip is based on this principle.
Speed control typically employs a PWM (Pulse Width Modulation) mechanism. The microcontroller uses a timer to generate a PWM wave with a variable duty cycle or directly outputs waveforms of different sizes via hardware PWM to control the overall speed of the vehicle.
Stepper motor
A stepper motor is an open-loop control unit that converts electrical pulse signals into angular or linear displacement. Under non-overload conditions, the motor's speed and stopping position depend only on the frequency and number of pulse signals, and are unaffected by load changes. When the stepper driver receives a pulse signal, it drives the stepper motor to rotate a fixed angle in a set direction, called the "step angle." Its rotation occurs step by step at fixed angles. The angular displacement can be controlled by controlling the number of pulses, thus achieving accurate positioning; simultaneously, the motor's speed and acceleration can be controlled by controlling the pulse frequency, thus achieving speed regulation.
Servo motor
Servo motors, also known as actuator motors, are used as actuators in automatic control systems to convert received electrical signals into angular displacement or angular velocity output on the motor shaft. They are divided into two main categories: DC and AC servo motors. Their main characteristic is that they do not rotate when the signal voltage is zero, and their speed decreases uniformly as the torque increases.
Servo motors primarily rely on pulses for positioning. Essentially, a servo motor receives one pulse and rotates by the angle corresponding to that pulse, thus achieving displacement. Because servo motors themselves have the function of emitting pulses, they emit a corresponding number of pulses for each rotation angle. This creates a feedback loop, or closed loop, between the pulses received by the servo motor and the pulses emitted. In this way, the system knows how many pulses were sent to the servo motor and how many were received, enabling precise control of the motor's rotation and achieving accurate positioning down to 0.001mm.
DC servo motors are further divided into brushed and brushless motors. Brushed motors are low in cost, simple in structure, have high starting torque, wide speed range, and are easy to control. However, they require maintenance, which is inconvenient (replacing carbon brushes), and they also generate electromagnetic interference, requiring specific environmental conditions. Therefore, they are suitable for cost-sensitive general industrial and civilian applications.
