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1、 Understanding of dead zone, hysteresis, positioning accuracy, input signal resolution, and centering performance in servo control
Due to signal oscillation and other reasons, the input signal and feedback signal of each closed-loop control system cannot be completely equal, which involves the problem of control dead zone and hysteresis. The system cannot distinguish the difference range between the input signal and feedback signal, which is the control dead zone range.
Due to signal oscillation, mechanical accuracy, and other reasons, the automatic control system of the servo always makes adjustments in a small range outside the control dead zone. In order to prevent the servo from adjusting to oscillations in a small range, the hysteresis effect needs to be introduced.
The hysteresis control dead zone is relatively large, with a general control dead zone range of ± 0.4%. The hysteresis loop can be set to ± 2%.

 

The difference between the input signal and the feedback signal does not cause the motor to move within the hysteresis loop. The difference between the input signal and the feedback signal enters the hysteresis loop, and the motor begins to brake and stop.
The positioning accuracy depends on the overall accuracy of the servo system, such as control dead zone, mechanical accuracy, feedback potentiometer accuracy, and input signal resolution. The input signal resolution refers to the minimum resolution range of the servo system for the input signal, and the input signal resolution of digital servo is much better than that of analog servo. The return performance depends on hysteresis and positioning accuracy.

 

 

2、 Why does the servo always make a squeaking sound
The servo always makes a squeaking back and forth positioning adjustment sound, because some servos do not have hysteresis adjustment function, and the control dead zone range is adjusted to be small. As long as the input signal and feedback signal always fluctuate, and their difference exceeds the control dead zone, the servo will send a signal to drive the motor.
In addition, without hysteresis adjustment function, if the mechanical accuracy of the servo gear set is poor, the tooth virtual position is large, and the rotation range of the feedback potentiometer exceeds the control dead zone range, the servo will inevitably adjust continuously and squeak incessantly.

 

3、 Why do some servos explode and burn circuit boards easily
Some servos use power devices with the same current. The system is designed with overcurrent protection function or the chip is equipped with overcurrent protection function, which can detect blocked current and short circuit status and quickly stop the motor drive signal. Additionally, a varistor can be connected to the motor circuit to prevent momentary overvoltage, and an absorbing capacitor can be designed at the front end of the power device. This type of servo motor is not easy to burn circuit boards and motors due to engine blockage caused by explosion. It has no absolute relationship with whether the servo is made of metal teeth or plastic teeth.

4、 Why does the servo shake
The control dead zone is sensitive, and the input and feedback signals fluctuate due to various reasons, causing the difference to exceed the range and the rudder arm to move, resulting in rudder shaking.

 

5、 General fault diagnosis of servo motor
1) After the explosion, the servo motor spun wildly, the steering wheel rocker arm was uncontrolled, and the rocker arm slipped.

It can be concluded that the gear has been swept and replaced.
2) After the explosion, the consistency of the servo motor decreased sharply. The phenomenon is that the damaged servo motor has a slow response and severe heating, but it can run with the control instructions, but the rudder amount is very small and slow.

Basic conclusion: The servo motor has overcurrent. After removing the motor, it was found that the no-load current of the motor was very high (>150MA), and it lost its intact performance (intact motor no-load current ≤ 60-90MA). Replace the servo motor.
3) After the explosion, there was no response from the servo after turning the rudder.
Basic determination: If the electronic circuit of the servo motor is broken, the contact is poor, or the driving part of the motor or circuit board of the servo motor is burned out, first check the circuit, including the plug, motor lead, and servo motor lead for any open circuit phenomenon. If not, eliminate them one by one. First, remove the motor and test the no-load current.

 

If the no-load current is less than 90MA, it means the motor is good, and the problem is definitely caused by the servo motor drive burning out. There are 2 or 4 small patch transistors on the 9-13g micro servo motor circuit board, which can be replaced. If there are 2 transistors, they must be directly replaced with Y2 or IY, that is, SS8550. If there is an H-bridge circuit with four transistors, it can be directly replaced. Replace with 2 Y1 (SS8050) and 2 (SS8550) directly, UYR of 65MG - use Y1 (SS8050 IC=1.5A); UXR -- Replace directly with Y2 (SS8550, IC=1.5A).
4) If the servo motor fails, the rocker arm can only rotate on one side and not move on the other side.
Judgment: The servo motor is in good condition. The main inspection is on the drive part. It is possible that one side of the drive transistor has been burned. Repair it according to (3).

 

 

5) After repairing the servo motor and turning it on, it was found that the servo motor was stuck in one direction and made a squeaking sound.
Conclusion: It indicates that the positive and negative terminals of the servo motor or the terminal wires of the potentiometer are connected incorrectly. Simply reverse the direction of the two connections of the motor.

 
6) After buying a brand new servo motor, I found that it was shaking wildly when powered on, but after using the control arm, everything was normal for the servo motor.
Conclusion: This indicates that the servo motor was assembled improperly or the gear accuracy was insufficient when it left the factory. This fault usually occurs on metal servo motors. If you do not want to return or replace them, the self solving method is to remove the servo motor back cover, separate the servo motor from the servo reduction gear, squeeze some toothpaste between the gears, put on the servo gear cover, put on the reduction gearbox screws, install the servo rocker arm, and repeatedly rotate the rocker arm by hand to grind the metal servo gear until the gear runs smoothly and the gear friction noise is reduced. After cleaning the servo gear with gasoline, install silicone oil on the gear and assemble the servo motor to solve the servo motor fault.

 
7) There is a type of malfunctioning servo that exhibits strange behavior: when the remote sensing is controlled by shaking, the servo has a normal response, but when the remote sensing is fixed to a certain position, the faulty servo arm is still slowly running, or the arm action is sluggish and moves back and forth.
After multiple repairs, it was discovered that the problem lies in the metal handle of the potentiometer, which should be tightly stuck in the last gear of the servo motor. It is not tightly connected to the large gear (last gear) of the servo arm, and even slips, causing the servo motor to be unable to correctly locate the position command issued by the control, resulting in inaccurate feedback and continuous searching.

 

After solving the tight connection between the potentiometer and the rocker arm gear, the fault can be eliminated. If the fault still exists after repairing according to the method, it may also be a problem with the servo motor or potentiometer, which needs to be comprehensively analyzed and investigated one by one!

 

8) If the faulty servo keeps shaking and eliminating radio interference, and the dynamic control arm still shakes.
Conclusion: The potentiometer is aging, replace it, or simply scrap it as a spare part!

 
9) After installing the digital tilt servo, it was found that the servo was not functioning properly, with varying speeds. It was returned to the manufacturer and even after replacing it with three, the consistency was still poor.
Conclusion: It was only later discovered that some digital servos require BEC, and after installing an external BEC of 5. V3A, the fault was resolved, regardless of the quality of the servos.