TECHNICAL SUPPORT
Published 2026-03-20
Many friends who have just started usingservos to make things often encounter this situation: theservos are obviously turning, but the mechanical arms, wheels or other mechanisms you want don’t move properly? Either the angle is wrong, or it's stuck, or it's shaking badly. Most of this troublesome problem lies in the key part that connects the steering gear and the actuator - the steering gear connecting rod. Only by understanding how to design connecting rods can your project truly take the first step.
Actually, the steering gear connecting rod is not as complicated as you think. It is just a rod that transmits motion and force. One end is connected to the steering arm on theservooutput plate, and the other end is connected to the component you want to drive. When the servo rotates an angle, the rudder arm moves with the pole, and the pole pushes or pulls the mechanism behind it, thus turning the limited rotation of the servo into the linear movement or more complex swing you need.
You can think of it as the driving wheel of a train. The big iron rod connecting the wheel is the connecting rod, which turns the reciprocating motion of the piston into the rotation of the wheel. In turn, the servo link converts rotational motion (within a certain angle) into the action you need. Once you understand the principle of motion conversion, you will have a good idea when designing, and you will know how to achieve the desired motion effect by changing the length and connection points of the connecting rods.
There is no need to calculate the length accurately at the beginning. Let’s have a general direction first. The basic principle is: it depends on how much travel or swing angle you ultimately need. For example, if you want a mechanical claw to open 5 centimeters wide, then you have to push back the approximate length of the connecting rod according to the maximum angle that the servo can rotate (usually 90 degrees or 180 degrees). Simply remember, if you want a greater stroke, use a longer connecting rod; if you want greater power, use a shorter connecting rod, because it saves effort but not distance.
There is a very practical and stupid way, which is to first cut out a model of the connecting rod from cardboard, then fix it on the steering wheel and mechanism with thumbtacks, and then use your hands to simulate rotation to see if the movement trajectory and stroke are correct. It's like building a house before building a model to see the effect. It allows you to discover unreasonable design issues in time, such as whether it will get stuck in a certain position or the stroke is not long enough. Once this step is done, it can help you save a lot of wasted money on processing materials later. I highly recommend you try it.
How can the connecting rod itself be firmly fixed to the steering wheel (that is, the disc on the steering gear shaft)? The most common and safest way is to use screws and copper posts. There is usually a circle of small holes on the steering wheel. Choose the appropriate hole position and use screws to screw the connecting rod or a special small connector on the steering wheel. There is a detail to pay attention to here. The screws must be tightened. It is best to put a little screw glue on the threads. Otherwise, as soon as the servo is turned, it will vibrate a few times and the screws will loosen, and everything will be in vain.
How is the other end of the connecting rod connected to the part driven by it (such as a wheel bracket)? At this time, a "joint" that can rotate flexibly is needed. You can put a ball stud on the connecting rod head, attach a ball stud to that part, and then snap the ball stud on. In this way, when the connecting rod is pushed or pulled, the joint can freely rotate at a small angle, making the entire mechanism much more flexible and less likely to get stuck. It's kind of like the way your shoulders are connected, both strong and flexible.
After hard work, I installed it, and when I turned on the power, my dear, the connecting rod was shaking like a sieve. What's going on? Usually the first reason is that the connecting rod itself is too soft. You may use thin plastic sheets or thin wooden strips. When the servo exerts force, it will first bend by itself, produce elastic deformation, then recover, deform again, and start shaking. The solution is straightforward. Switch to a more rigid material, such as a thicker carbon fiber plate or a thin aluminum sheet. The vibration can often be reduced immediately.
The second common reason is that the "virtual position" is too large. What is a virtual position? It's the gap in the connection. For example, the gap between the ball head buckle and the ball head is large, or the screw hole is one circle larger than the screw. The accumulation of these gaps will cause the servo to move, but when the force is transmitted to the back, part of it has been shaken off due to the gap, causing vibration. To solve this problem, you need to check all connection points, replace the ball joint with a more precise one, or put a small spacer on the screw to eliminate the gap. Adding a little lubrication to the moving joints can also make them move more smoothly and reduce unnecessary shaking.
For those who are just getting started, or making some verification gadgets, I most recommend you to use ABS plastic boards or acrylic boards. This thing is cheap and easy to process. You can break it with a few strokes with a hook knife, or you can even get it with a handsaw. If you want to make a hole, a regular electric drill will do. Use it to quickly verify whether your linkage can move and whether the stroke is correct. The cost is very low, and you won't feel bad even if you make a mistake.
After you have verified it and want to make something stronger and practical, you have to change the material. In pursuit of light weight and high strength, carbon fiber panels are the first choice and are used by many model aircraft and robots. If the project is particularly stressed, such as making a large-torque robotic arm, then metal parts, such as aluminum alloy or steel, will be needed. How to choose actually depends on your needs: use plastic for simple verification, use carbon fiber for performance, and use metal for heavy-duty applications. You can search for "carbon fiber customization of steering gear connecting rod" online and you can find many businesses that provide professional cutting services.
Sometimes you have this requirement: you want the servo to turn 60 degrees so that the end mechanism can swing 120 degrees, or conversely, you want to use a small turning angle to move the mechanism a long distance. This involves a concept called "transmission ratio". To put it simply, if the connection point of the connecting rod on the steering arm is very close to the rotation center of the steering gear, and the other end is far away from the rotation center of the mechanism, then the steering gear will rotate a little, and the end will move a lot, but at the cost of less force at the end.
You can estimate this when designing: the ratio of the input moment arm (the distance from the connection point on the rudder arm to the center of the steering gear) and the output moment arm (the distance from the connection point on the mechanism to its own rotation center) determines the changes in motion and force. The input moment arm is short and the output moment arm is long, which means "save distance and waste effort". Although we don’t need to use a calculator to calculate accurately when we first get started, but with this concept of proportion in mind, when you draw a sketch on paper and select the hole position on the steering wheel, you can achieve the fast or powerful effect you want more purposefully, instead of relying entirely on blind guesses.
What was the biggest pitfall you encountered when designing the steering gear linkage? Or do you have any unique tips? Come and share it in the comment area. If you find it useful, don’t forget to like and share it with more friends who play servos!
Update Time：2026-03-20
Contact Kpower's product specialist to recommend suitable motor or gearbox for your product.
