TECHNICAL SUPPORT
Published 2026-02-16
Recently, many friends who play robots have been asking why theservosuddenly stopped turning. When I broke it with my hand, it was stuck tightly, which really gave me a headache. Don’t worry, this is usually theservosending a distress signal to you. Today we will talk about what to do if you encounter this situation.
When you find that theservocannot be turned with your hands, the most direct reason is probably that the gear is stuck. Inside the steering gear is a set of precision plastic or metal gears. If it is impacted by external forces or overloaded for a long time, the gears may become dislocated or even chipped. This is like a bicycle chain that is stuck and physically cannot rotate.
Another possibility is that the motor is burned out or the driver chip is broken down. If the DC motor inside the steering gear is blocked for too long, the current will increase sharply, causing the coil to burn out and the entire rotor to be magnetically locked. In this case, even if the external gear is intact, you will feel that it is as motionless as a lump of iron.
If the servo is stuck and is not dealt with in time, the most direct risk is to burn out your driver board. Because the servo is stuck and the motor is in a stalled state, the current will surge to several times the normal value. If the power supply does not have overcurrent protection, this large current may flow back to the control board and burn the chips on it.
For a running robot, a stuck servo may trigger a chain reaction. For example, on a robotic arm, if one joint suddenly locks, other joints will have to bear greater torque in order to complete the action, which can easily lead to more overload damage to the servos. It's like dominoes, one small problem can ruin the entire project.
You can first hold the steering wheel with your hands and shake it gently to feel the size of the gear. If you feel there is obvious looseness but it just won't turn, it's probably because the gear is worn and stuck. At this time, when you disassemble the steering gear, you can usually see white plastic debris in the gear box, which is ironclad evidence of gear wear.
If the servo feels very tight and has no empty position at all, as if it is being attracted by a strong magnet, it is probably a circuit problem. You can smell whether the servo has a burnt smell, or use a multimeter to measure the resistance between the positive and negative poles of the power supply. If it is close to zero ohms, it means that the driver chip has broken down and short-circuited.
If the gear is stuck, you can try to perform "minor surgery" on the steering gear. Carefully disassemble the back cover, take out the gear set, and check which teeth are damaged. If it's just a minor burr, smoothing it out with fine sandpaper and re-greasing it will often get it running again. It's like putting a little oil on a rusty door shaft, the effect is immediate.
If it is a circuit problem, the situation is more difficult. You can cut off the servo wire, keep only the feedback wire of the potentiometer, and then connect an external motor drive module to convert the ordinary servo into a planetary reduction motor. This is a great way to use waste, at least you don’t have to throw it directly into the trash can.
It is key to leave sufficient torque margin when selecting the model. Many people like to stick to the limit. For example, if they calculate that they need 5 kilograms of torque, they buy a 5 kilogram servo. However, there will be inertial impact during actual movement, so it is best to choose a servo with more than twice the torque requirement. It's like buying a car. You can drive it with a 1.0L displacement, but it won't be able to drive uphill.
When installing, make sure that the steering gear shaft and the load rotating shaft are concentric. If the two are not concentric, the servo will bear additional radial force every time it turns, and the gears will wear out very quickly. You can use couplings or design floating structures to compensate for installation errors. This small detail can extend the life of the servo several times.
If you find after disassembly and inspection that the gearbox has been broken into pieces or the circuit board has obvious burn marks, don't bother with it. The maintenance cost is often more than buying a new one, especially for some plastic gear servos that cost tens of dollars. It is more worry-free to just replace them with new ones. It's like the screen of a mobile phone is too broken. It's better to replace the screen with a new one.
If your project is participating in a competition, or if the servo of the equipment delivered to the customer is stuck, it is recommended to replace it with a new servo. Reliability is the first priority, and a repaired servo may break down at a critical moment. Remember, the steering gear is a consumable item, so replace it when it’s time to replace it. Don’t lose the big for the small.
What's the most difficult servo failure you've ever encountered while debugging a robot? Welcome to share your experience in the comment area. If you find it useful, don’t forget to like and forward it so that more friends who play servos can see this article.
Update Time：2026-02-16
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