Servo motor
Servo motor internal structure
The servo motor includes a small DC motor; a set of shifting gear sets; a feedback adjustable potentiometer; and an electronic control board. Among them, the high-speed rotating DC motor provides the original power, drives the shifting (deceleration) gear set to produce a high-torque output, the larger the gear ratio of the gear set, the greater the output torque of the servo motor, that is, the more Withstand greater weight, but the speed of rotation is also lower. Its structure is as follows:
How the servo motor works
The servo motor is a typical closed-loop feedback system. The principle can be as follows:
The reduction gear set is driven by a motor, and its terminal (output) drives a linear proportional potentiometer for position detection. The potentiometer converts the corner coordinate into a proportional voltage feedback to the control circuit board, and controls the circuit board to control it and the input. The pulse signal is compared to generate a correction pulse and drive the motor to rotate in the forward or reverse direction so that the output position of the gear set coincides with the desired value, so that the correction pulse tends to be zero, thereby achieving the purpose of accurately positioning the servo motor.
How to control the servo motor
The standard micro servo motor has three control lines: power, ground, and control. The power and ground lines are used to provide the internal DC motor and the energy required to control the line. The voltage is usually between 4V and 6V. The power supply should be isolated from the power supply of the processing system as much as possible (because the servo motor generates noise). Even a small servo motor pulls down the voltage of the amplifier during heavy loads, so the ratio of power supply to the entire system must be reasonable.
Input a periodic forward pulse signal. The high-level time of this periodic pulse signal is usually between 1ms and 2ms, while the low-level time should be between 5ms and 20ms. It is not very strict. The table below shows The relationship between the positive pulse width of a typical 20ms periodic pulse and the output arm position of a micro servo motor:
Servo motor power lead
There are three power leads, as shown in the figure. The red line in the three lines of the servo motor is the control line and is connected to the control chip. In the middle is the SERVO working power cable, the general working power is 5V. The third is the ground.
Servo motor speed
The instantaneous speed of the servo motor is determined by the fit of its internal DC motor and the shifting gear set. The value is unique under constant voltage drive. However, the average speed of movement can be changed by the control method of segmentation pause. For example, we can subdivide the rotation with the action range of 90o into 128 pause points, and realize the change of 0o-90o by controlling the length of each pause point. The average speed. For most servo motors, the unit of speed is determined by "degrees/second".
Precautions for using a servo motor
Unless you are using a digital servo motor, the above servo motor output arm position is only an inaccurate number. Ordinary analog micro servo motors are not a precise positioning device. Even with the same brand of miniature servo motor products, the difference between them is very large. When the same pulse is driven, different servo motors have a deviation of ±10o. It is also normal.
For the above reasons, it is not recommended to use a pulse of less than 1ms and more than 2ms as the drive signal. In fact, the initial design of the servo motor is only in the range of ±45o. Moreover, when this range is exceeded, the linear relationship between the rotation angles of the pulse widths also deteriorates. Pay special attention to never load a pulse signal that causes the servo motor output position to exceed ±90o, otherwise it will damage the servo motor's output limit mechanism or gear set and other mechanical components.
