TECHNICAL SUPPORT
Published 2026-02-27
Have you ever encountered this situation when playing with aservo: The program is written correctly and the motor is spinning, but theservojust keeps shaking, or makes a clicking sound when turning, and breaks down within a few days? Don't be too quick to doubt the quality of theservo. Eighty percent of the trouble is caused by the small part of the connecting shaft. As someone who has been involved in DIY projects for several years, today I will talk to you about the servo connecting shaft to help you avoid those pitfalls.
If the connecting axis is not selected correctly, the most direct manifestation is that the servo responds slowly, showing a half-beat slow state. I originally expected the robotic arm to grab items accurately, but instead it moved slowly, which was really worrying. What's even more troublesome is that when there is a gap between the shaft and the output end of the servo, it will shake left and right during rotation, making the positioning always inaccurate. Over time, this mismatch can also cause wear on the gears inside the servo. A steering gear that could have been used normally for several years may become scrapped in just a few months. When I first got involved in this field, I was ignorant. It was precisely because of the problem of the shaft that several servos were abandoned. It was not until later that I discovered that it was this subtle link that was secretly causing trouble.
In actual operation, the correct choice of connecting shaft is crucial. Once the wrong choice is made, the response speed of the servo will be greatly reduced, just like the slowness of a robotic arm when grabbing something, which will undoubtedly affect the efficiency of the entire work process. The gap problem between the shaft and the output end of the servo cannot be underestimated. It will cause left and right shaking during rotation, seriously reducing the positioning accuracy. If this happens for a long time, the internal gears of the steering gear will be damaged, and the life of the originally durable steering gear will be greatly shortened. I didn't notice this at first when I was playing, and I scrapped several servos one after another. Later, after careful study, I realized that it was this small, easily overlooked detail that caused a series of problems.
Determining model matching is actually not complicated. You must first look at the shape. There are usually two common shapes at the output end of the servo, one is the cross type and the other is the semicircular type. The semicircular type is also called a spline. You need to hold the connecting shaft and compare it with the servo to make sure the shape fits perfectly.
Then look at the number of teeth, such as the common 25T and 21T. The numbers here represent the number of teeth of the servo, that is, there are 25 teeth or 21 teeth respectively. You must count them carefully. Finally, check the hole diameter. If the shaft is placed outside the servo, then the inner diameter of the shaft must be just enough to fit in. It cannot be too large or too small. When these conditions are met, there will basically be no matching errors.
️ Step 1: Observe the shape of the servo output end
️ Step 2: Count the number of teeth on the output end of the servo
️ Step 3: Use a caliper to measure the diameter of the output end
️ Step 4: Test-install the selected connecting shaft and see
It depends on what project you are doing. If it is a toy car for children, plastic is enough, it is cheap and light, and the steering wheel is light to operate. But if you want to make a robotic arm or robot leg that needs to withstand a lot of force, it must be made of metal. I have a friend who makes a racing robot. The plastic rudder arm he used broke off halfway through the race, and all the previous efforts were wasted. Although metal ones are more expensive, they hardly deform and last much longer. To put it simply, if you want to play, choose plastic, and if you want to do serious work, choose metal.
The most common mistake during installation is to tighten the screws too much. Many people think that the tighter they are, the more stable they will be. However, they screwed the plastic teeth on the output end of the servo and caused them to be scrapped. The correct way is to tighten it until you feel some resistance.
Regarding the installation of the servo, it is also necessary to knock the teeth in if they are not in the correct position, which will damage the teeth. You should slowly align it before pushing. If you can't push it in, turn the steering wheel and try again. In addition, don’t forget to put a little bit of screw glue on the screws to prevent them from loosening during use. This detail can make your device much more stable.
For high-speed movements such as aircraft models and ship models, you should choose ones with a limit design to prevent the rudder surface from being blown out of position by the wind. When making a photography gimbal, accuracy is the most important thing. You have to choose one that works with the servo and has almost no false position, otherwise the video will be shaken. If you are building a smart home, such as an automatic window opener, you should consider long-term durability, waterproof and rust-proof stainless steel materials, which are more suitable. You see, the requirements for shafts are really different in different places. Before buying, you have to think clearly about what your project is mainly for.
In fact, a signal will be sent out when the connecting shaft is about to be damaged. When you notice that the sound of the servo is louder than before, or there is always overshoot at a certain position, and the return position is inaccurate, in this case, it is very likely that the shaft is worn. At this time, gently move the rudder arm with your hand. If you can clearly feel the gap, it means that the fit has become loose. In addition, carefully observe the surface of the shaft. If there is rust or deformation, this is actually a warning to you that the connecting shaft is about to have a problem. Being able to detect these signs in time and replace them can prevent it from malfunctioning at a critical moment, like a robot that is performing a performance suddenly paralyzing.
There is another situation that can also indicate that the connecting shaft is about to break. For example, during operation, you find that the movement of the servo becomes sluggish and is no longer as sensitive as before. This may also be a sign that the shaft is about to be damaged. Moreover, when the servo is running, it will occasionally get stuck. This is also likely to be a problem with the connecting shaft. Look at the connection between the shaft and other components. If there are signs of looseness and some minor signs of wear can be seen, it means that the condition of the shaft is not optimistic. Once these signs are discovered, replacing the connecting shaft as soon as possible can avoid such a bad situation as the robot suddenly losing control during an important performance.
Having said so much, I wonder if you now know how to choose the servo connection axis? What is the most troublesome problem you have encountered while playing with steering gear? Welcome to chat in the comment area. If you find it useful, don’t forget to give it a like and share it with other friends!
Update Time：2026-02-27
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