TECHNICAL SUPPORT
Published 2026-03-16
Many friends useservos to do projects, but when they encounter situations where theservos do not turn, vibrate or have no power, they are often confused and do not know where to start troubleshooting. In fact, to really play with theservo, you must first understand its "heart" - how the main circuit of the servo works. To put it bluntly, the main circuit is the part of the hardware that is responsible for converting electrical energy into mechanical energy and driving the motor to rotate. Once you understand it, you can predict the performance of the servo and quickly find the cause if something goes wrong.
You can think of the main circuit of the steering gear as the engine and transmission system of a car. Its core task is to receive instructions from the controller and then drive the motor to rotate honestly. A typical steering gear main circuit mainly consists of a power switching device (the most common one), a DC motor body, and an essential protection circuit. These are like several super-responsive faucets, specifically responsible for controlling the size and direction of water flow to the motor.
Taking it apart specifically, the core of the main circuit is a structure called "H bridge", which consists of four hand-in-hand. In addition, there is usually a small resistor to monitor the current in real time (like a water meter), and some large capacitors to stabilize the voltage (like a small reservoir). It is these components that work together to allow the output shaft of the servo to accurately rotate to the angle you want.
When the control circuit (that is, the brain of the servo) analyzes your command signal, it will tell the main circuit: "Now you need to turn in this direction!" At this time, the driver chip in the main circuit will act like a band conductor, accurately sending on or off signals to those ones. This process is extremely fast and can be repeated thousands of times per second.
For example, if you want the motor to rotate forward, the main circuit will conduct the upper left and lower right corners of the H bridge. At this time, the current will start from the positive pole of the power supply, pass through the upper left corner, pass through the motor, and then flow back to the negative pole through the lower right corner, and the motor will spin steadily. Want to reverse it? Then just connect the upper right and lower left ones and let the current flow through the motor in the opposite direction.
You may ask, why is it so complicated to control the forward and reverse rotation of the motor? Because the motor needs to rotate in both directions to achieve position servo. A simple switch can only control the motor on and off, but cannot reverse it. The ingenuity of the H-bridge is that it uses the alternating cooperation of four switches, like a bridge, to allow current to flow through the motor from left to right or from right to left, thus easily achieving forward and reverse rotation.
And the benefits of H-bridges go far beyond that. Combined with PWM (Pulse Width Modulation) technology, it can also finely control the motor's speed. By switching extremely quickly and adjusting the effective voltage at both ends of the motor, the speed can change accordingly. What's even more powerful is that the H-bridge can also brake the motor instantly (for example, directly short-circuiting both ends of the motor), which greatly improves the response speed and control accuracy of the servo.
The word PWM sounds very professional, but in fact the principle is very simple. You can think of it like turning a faucet on and off quickly, adjusting the amount of water by controlling the proportion of time it flows. The PWM signal is a series of voltage pulses that change high and low. It controls the time ratio of the switch. We call this ratio "duty cycle". The larger the duty cycle, the longer the motor is powered and the faster it spins.
Assuming that the frequency of PWM is fixed, when the duty cycle is 50%, it means that it is on half of the time and off half of the time. The average voltage obtained by the motor is half of the power supply voltage, and the speed is almost half. When the duty cycle is adjusted to 100%, it is always on and the motor runs at full speed. The servo precisely adjusts the motor speed by changing the PWM duty cycle, and then cooperates with the feedback from the position sensor to finally make the output shaft stop stably at the target angle.
What happens if the servo loses its temper and stops turning? Don't worry, we can be detectives and start investigating from the main circuit. ️The first step is to listen to the sound. When the steering gear is working normally, the motor will make a subtle and even "sizzling" sound when it rotates. If there is no sound at all, it may be that the main circuit is not powered on at all; if the sound is harsh or intermittent, it may be burned out.
️The second step is to touch the temperature. After the servo has been working for a while, gently touch the outer shell with your hand (pay attention to safety). Under normal circumstances, there will be a temperature rise, but it will not be hot. If it instantly heats up or even smokes as soon as the power is turned on, it is probably because the upper and lower parts of the H-bridge are connected at the same time, which is a "straight-through short circuit". This is the most taboo fault of the main circuit. If possible, you can use an oscilloscope to see the PWM waveforms at both ends of the motor, which can be seen clearly at a glance.
When choosing a servo, don't just look at the torque and speed. The hidden parameters of the main circuit are the key. You have to learn to read the data sheet and focus on these: the operating voltage range, which determines whether your power supply can feed it; the maximum continuous current, which is directly related to how much load the servo can carry without burning out; and the supported PWM frequency range, make sure your controller can keep up with it.
I would like to give you two practical suggestions: First, estimate the maximum load current that the servo will bear in your project, and then choose a servo with a current capacity of more than 30%, so that it can be used safely. ️Second, determine the frequency of the PWM signal sent by your controller, and find the frequency range it can accept in the servo's specifications. Only by matching the two can you have fun playing. If you want to learn more about the detailed parameters of a certain servo, the best way is to directly search the brand's official website, download the latest technical specifications, or directly consult their application engineers, which are the most authoritative sources of information.
What "difficulties" have you encountered when using the steering gear? Welcome to share your experience in the comment area, let's discuss and solve it together!
Update Time：2026-03-16
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