TECHNICAL SUPPORT
Published 2026-03-26
When playing with robots or working on small projects, have you ever encountered such a situation: You have sent a command to theservoto return it to the straight position, but it always tilts its head, or it keeps shaking there? Don't worry, this is probably because theservo's median value is not calculated correctly. To put it simply, the median calculation of the SD5servois to find the PWM signal value that can truly return the servo to the mechanical neutral point. If this value is not found correctly, subsequent control accuracy will be impossible. Let’s clarify this matter today.
Wrong calculation of the steering gear's median value will lead to various abnormal situations in the steering gear and affect the operation of the entire project. Therefore, it is very important to accurately calculate the median value of the servo. Only by grasping this key point can the servo operate accurately as expected, thereby ensuring the smooth development of robots or small projects. Today we will focus on overcoming this problem and thoroughly understand the small matter of steering gear median calculation.
Many friends think that the servo is not nominally 90 degrees, which is the neutral position. Wouldn't it be enough to just give a theoretical value? Not really. Because of mechanical assembly errors, individual differences in the potentiometer inside the servo, and even the different loads you apply to the servo arm, its actual "neutral point" will deviate. If you don't calculate the actual median value, your steering wheel may never run straight, and the robotic arm may not be able to clamp things accurately. This step is like "zero calibration" for the machine, which is the basis for ensuring that it is obedient.
The most reliable way to calculate the median is not to rely on guessing, but to use the "dichotomy method" to test. You can first use the reference value given in the servo data sheet. For example, the usual PWM period of the sd5 servo is 20ms, and its corresponding median pulse width is about 1.5ms. First, write this value into the program, and then observe the position of the servo. If the servo moves to the left, then you reduce the pulse width value; if the servo moves to the right, then you increase the pulse width value. By continuously "taking the middle value", we gradually approach until the servo accurately stops at the point where there is no jitter at all and the angle is just right.
In this process, every adjustment to the pulse width value is crucial. Because only by accurately controlling the pulse width can the servo accurately reach the ideal position. Moreover, this "dichotomy" testing method can find the median value more efficiently, avoiding possible errors caused by blind guessing. It is a scientific and reliable method that can ensure the optimal operation of the steering gear and achieve precise angle control, thereby meeting the requirements for the position accuracy of the steering gear in various application scenarios.
If you don’t have a special programmer at hand, is it really impossible to adjust the median value? The answer is obviously no. In fact, you can use the most direct "manual hard adjustment method" to solve this problem. For example, take an STM32 development board, connect it to the computer, and then enter values directly into the serial monitor. Next, write a simple loop program that allows you to enter different PWM values through the keyboard. Each time you enter a number, the servo will move accordingly. At this point, you just need to sit there, input the values, and carefully observe the angle changes of the servo with your naked eyes until you find the perfect position. This method may seem a bit rustic at first glance, but it is undeniable that it is the most intuitive and effective method.
In actual operation, this manual hard adjustment method has unique advantages. It does not require complex programming skills and is very easy to use for beginners or people who only occasionally need to adjust the servo mid-range value. By directly inputting values in the serial monitor, you can see the movement of the servo in real time, thus accurately finding the ideal angle. Moreover, this intuitive method allows users to understand the working status of the steering gear more clearly and avoid errors caused by complex program logic. Although it may not be as efficient as some advanced methods, in certain scenarios, its simplicity and directness can play a huge role in helping people quickly and accurately complete the adjustment of the servo mid-value.
Inaccurate median values are not trivial and cause trouble throughout the entire project. The most direct consequence is that the servo "burns" quickly. Because the median value is wrong, the servo has been trying to correct to a wrong target position. The motor is stalled, the current increases, the heat is serious, and it will break down soon. In addition, if your project involves the linkage of multiple servos, such as a quadruped robot, and the median value of one leg is wrong, the gait of the entire robot will be unbalanced, making it limp when walking, or even unable to stand at all.
Let's actually go through the complete process. First of all, the first step is to connect the signal line of the SD5 servo to your control board accurately. The power supply must be sufficient. It is recommended to use a regulated power supply or a fully charged battery to ensure that the servo can operate normally.
The second step is to write a simple test code whose function is set to make the servo rotate to a specific value you input and stay at this value. The third step is to start from the theoretical median value. Assume that your PWM range is 0 to 1000, then start from the value of 500, carefully observe and record the position of the servo in detail. The fourth step is to perform the debugging operation repeatedly, just like playing a guessing game, until the servo stops firmly in the middle position.
If you feel that it is too troublesome to change the code and burn every time you debug, you can try the "servo tester" on the market. It was a small thing that cost a few dollars. It had a knob on it. You could turn the servo by just turning it, and you could also set the neutral position with one click. You can first use it to find the physical median value of the servo, write down the value corresponding to this position, and then write this value into your program. This small tool can help you save a lot of time in repeatedly burning programs, and is a powerful assistant in debugging the servo value.
Are you now ready to check the median value of the servo in your project? What strange phenomena have you encountered when debugging the steering gear? Welcome to share your experience in the comment area, and let’s communicate and avoid pitfalls together.
Update Time：2026-03-26
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