TECHNICAL SUPPORT
Published 2026-03-18
When we engage in product innovation, especially when it comes to things like robots, smart homes, or model airplanes,servos are definitely no stranger to us. But have you ever thought about why this littleservois so obedient that it never reaches 31 degrees when it is turned 30 degrees? In fact, the secret is hidden in its belly -the motor of the steering gear will have a"little tail", which is a feedback device. Without it, theservowould just be a fool who only knows how to turn around.
To put it bluntly, this is a closed-loop control problem. Imagine if you were asked to walk from point A to point B with your eyes closed. Would it be easy for you to go astray? The same goes for the steering gear. If there is no feedback, it only knows to "power on and turn", but it has no idea where to turn. The feedback device is like putting a pair of eyes on the steering gear, telling it in real time: "Hey, buddy, you have reached the position, stop quickly!"
Specifically, when you send a 90-degree command to the servo, the control circuit will energize the motor and let it rotate. At this time, the feedback device starts to work. It closely monitors the actual position of the motor shaft and continuously transmits the position information back to the control circuit. Once the control circuit compares and finds "Oh, it's not yet 90 degrees", it will continue to let the motor rotate; once it finds "exactly 90 degrees", it will immediately cut off the power and let the motor stop accurately. Just go back and forth like this to ensure the accuracy of each movement.
The most common feedback device is a small component called a "potentiometer". You can think of it as a variable resistor controlled by the rotation angle. When the servo rotates, it will drive the potentiometer knob to rotate together. Turn to different angles, the resistance value of the potentiometer is different, and the voltage generated is also different. The control chip in the steering gear can infer the current angle by reading this voltage value. Just like the knob switch in our home, the light will be brighter wherever it is turned. The principle is somewhat similar.
Of course, technology is also advancing, and now some high-end digital servos are beginning to use magnetic encoders for feedback. This one is much more advanced. It determines the angle by sensing changes in the magnetic field. There is no physical contact, so it hardly wears out. Its accuracy and lifespan are higher than traditional potentiometers. However, most of the cost-effective servos currently available to us still use reliable and cheap small potentiometers.
If there is something wrong with the feedback device, the steering gear will immediately go "insane". The most typical symptoms are shaking, buzzing, and swinging back and forth like a pendulum, but unable to stop at a fixed position. This is because the control circuit cannot receive a correct and stable position signal. It thinks it has not reached the place, so it desperately energizes the motor. As a result, the motor rotates, the feedback signal changes again, and the circuit orders it to rotate back, so it tosses back and forth near the target position until it burns out or you lose power.
Also, the servo becomes weak, or the range of motion becomes strange. For example, if you ask it to rotate to 90 degrees, it may feebly rotate to 45 degrees and then stop. This is all because the signal given by the feedback device is inaccurate, and the control circuit is misled and makes wrong judgments. When encountering this situation, don't throw it away in a hurry. You can first check whether there is a problem with the feedback potentiometer. Sometimes the contacts inside it are dirty or worn.
For most of us ordinary players and product developers, the most common choices are analog servos and digital servos. Analog servos basically use traditional potentiometer feedback. The technology is mature and the price is cheap. It is completely sufficient for models and small robots where the requirements are not too extreme. If it breaks, you don’t have to worry about replacing it.
If your project has higher requirements for accuracy, response speed and holding force, such as being used in joints of robotic arms or in places that need to withstand external forces for a long time, then digital servos with magnetic encoder feedback will be a better choice. Although more expensive, it responds faster, has more accurate positioning, and because there is no physical wear and tear, has a much longer lifespan, making it more reassuring in critical applications. In a word, it depends on your budget and performance needs.
Of course, many electronic enthusiasts like to do this. This is the most economical way to repair old servos. But you have to have some soldering and disassembly skills. First, you need to carefully open the servo housing, remembering the order of the internal gears, and then use a solder suction tool to suck out the tin on the three pins of the old potentiometer and remove it. Next, find a potentiometer of the same model and solder it on. Pay special attention to this step. The center position (that is, the initial angle) of the new potentiometer must be consistent with the original one, otherwise the center position of the servo will be offset.
After welding, put the gear back as it is and tighten the screws. It's easy to say, but it requires patience to do it, especially cleaning the pads and keeping the gear meshing correctly. If you are not confident in your workmanship, or the servo is very cheap, it may be more worry-free to just buy a new one. But this is indeed a good opportunity to learn the internal structure of the servo, and the sense of accomplishment in repairing one is quite high.
It can rotate, but it is not a servo, but an ordinary DC geared motor. You can directly energize the two wires of the motor, and it will keep spinning with the gearbox until you cut off the power. In this way, you completely lose control of the angle and position, and can only control whether it rotates or not. In some scenes that only require continuous rotation, such as car wheels, this is no problem.
But back to our topic, once you need to precisely control the position, for example, if you want a gimbal camera to focus on a certain target, or to have a manipulator accurately grab something, the motor without feedback will be completely blind. It doesn't know where it is, so it can't follow your instructions to get to the right place. It's like asking you to drive to a strange place without giving you a map or road signs, so you can only drive aimlessly. Therefore, the reason why the steering gear is called a steering gear is because of this feedback device.
Have you ever disassembled a steering gear and seen with your own eyes the "little tail" that works silently? Share your experiences in the comments section! If you find the article useful, don’t forget to like and share it to let more friends know this little knowledge.
Update Time：2026-03-18
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