TECHNICAL SUPPORT
Published 2026-03-05
When playing with theservo, it is really confusing to encounter a situation where theservostops after "just turning once". I originally wanted to let it swing back and forth, but it stopped when it moved. What is the problem? In fact, there are often several key points hidden behind this that are easily overlooked. Once you understand them, the problem will naturally be solved. Let’s clarify this matter together.
If the servo only moves once, the most intuitive reason is that there is something wrong with the control signal. The steering gear determines which angle it should turn by receiving continuous PWM (pulse width modulation) signals. It is like an obedient soldier, always waiting for the command of the commander (microcontroller). If the signal only comes for a moment and then is interrupted, or the signal itself is unstable, the servo will naturally only execute that command and then stop in place to "stand by". You have to check in the code to see if the rotation command is only sent once and not looped to keep it working.
In addition, don’t ignore the performance issues of the servo itself. Some servos with low power or average quality will also experience this "draught" phenomenon when encountering high resistance or insufficient voltage. You can gently move the servo arm with your hand to feel if there is any jamming. If it is powered by a battery, try replacing it with a new battery or using a regulated power supply to see if it is a "suspended death" caused by insufficient power supply.
When encountering discontinuous rotation of the servo, we can start with the simplest code troubleshooting. In your or other controller's program, check to see if the part that controls the servo is only executed once. Usually we need to useforloop orwhileloop, combined withdelay()microsecond delay function, to continuously send changing PWM values to the servo. For example, let the servo slowly turn from 0 degrees to 180 degrees, and then turn back from 180 degrees, so that continuous swing can be achieved.
If there is no problem with the code, then you need to look at the type of servo. The response methods of ordinary analog servos and digital servos are slightly different. Digital servos process signals faster, but the programming logic is the same. Another possibility is that the servo has insufficient torque and cannot move your mechanical structure. You can first remove the servo arm and let it idle to test it. If the idling is smooth, then 80% of the time the load is too heavy and you need to replace the servo with a larger torque, or add some lubricant to your linkage mechanism.
The control lines of the servo are more sensitive to interference, especially when your wiring arrangement is messy. If the motor wires, power wires and signal wires are tightly tied together, the electromagnetic interference generated when the motor rotates can easily penetrate into the signal wires, causing the servo to receive wrong instructions, which manifests as shaking, no rotation, or only one rotation. Therefore, when wiring, try to keep signal lines away from high-current power lines, or use shielded wires to enhance anti-interference capabilities.
Additionally, your controller itself may be a source of interference. If your main control board is also driving other high-power devices, such as DC motors or electromagnets, instantaneous fluctuations in the power supply will distort the control signals of the servo. The solution is to add a large capacitor filter to the power supply end, or use an independent power supply to power the servo, and only share the ground wire with the controller, so as to minimize interference.
Insufficient power supply is one of the culprits of the servo "only turning once". When the servo is started, a relatively large current is needed to overcome the static friction. If the power supply cannot provide such a large current, the voltage will be pulled down instantly, causing the control chip inside the servo to "power off and restart". It will only shake or rotate once and then stop. What is particularly obvious is that when you gently help it rotate with your hands, it can continue to work. This is a typical power shortage.
You can pay attention to the specifications of the servo, which will indicate its operating voltage (usually 4.8V-6V) and stall current. The locked-rotor current of an ordinary 9g servo may reach several hundred milliamps, and the high-torque servo motor can easily reach several amperes. If you are using a battery box, it is recommended to use a multimeter to measure the voltage at no-load and load conditions. If the voltage drops seriously, you will need to use a larger-capacity battery or a UBEC (battery elimination circuit) with a BEC (voltage stabilizing circuit) to provide separate power to the servo.
Many times, the problem lies in the code we write, especially those who are just getting started. A common mistake is to write rotation instructions insetup()function, causing the program to be executed only once at startup. The correct approach is to put the continuous instructions for turning the servo inloop()loop. For example, if you want the servo to swing back and forth, you must continuously change the angle value inloop(), and allow enough time for the servo to move to the specified position after each change.
Another thing to note is the frequency and resolution of the PWM pins. Different library functions have different support for servos. For example, theServo.hlibrary is very convenient to use, but it takes up timer resources. If you are using other PWM pins to directly output signals, make sure the frequency is around 50Hz, which is a period of 20ms, and the high level time is between 0.5ms and 2.5ms, so that it can correspond to the range of 0 to 180 degrees. If you write the wrong pulse width, of course the servo will not move as you want.
Each servo has its own physical rotation limit. Common servos are from 0 to 180 degrees, but there are also "continuous rotation servos" that can turn 360 degrees. The usage of these two is completely different. If you take a regular servo and try to give it a value beyond 180 degrees in the code, it will either get stuck at the limit and buzz, or it won't turn at all. So the first step is to confirm your servo type and its approximate range of rotation.
Even if the servo is a standard 180 degrees, there are subtle differences in the neutral and extreme positions of different brands and models. You may need to experiment in your code to fine-tune the minimum and maximum PWM values. For example, when using.write(0), it does not go to the end, then you need to adjust the pulse width parameters to ensure that it can accurately execute your instructions. Only when the angle range is set accurately can the servo obediently obey your instructions.
The smoothness of the mechanical structure directly affects the performance of the steering gear. If the linkage connecting the servo arm is too tight, or there is interference at a certain point, the servo will get stuck when it turns here. At this time, the servo will protect itself due to overcurrent and stop rotating, or it will only rotate once because it cannot overcome the resistance. You can disconnect the servo from the connecting rod and move the entire mechanical structure with your hands to feel whether there is a dead point that is particularly laborious.
If it is indeed mechanically stuck, you need to modify the design of your 3D printed or metal parts, increase the gap, or adjust the installation position. Another possibility is that the internal gears of the servo are out of gear, which is usually accompanied by a clicking noise. If the gear is broken, it is basically impossible to repair it and can only replace the steering gear with a new one. Therefore, it is also important to regularly check the health of the mechanical structure and the steering gear itself.
Okay, let’s stop talking about the problem ofthe servo turning only once. I wonder if you have encountered any particularly weird problems when debugging the servo? Welcome to share your "rollover" experience in the comment area, let's communicate and avoid pitfalls together. If you find the content useful, don't forget to like it and share it with more friends who need it!
Update Time：2026-03-05
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