TECHNICAL SUPPORT
Published 2026-03-21
The steering gear rotates forward and reverse. At first glance, it sounds like a simple matter. However, when it is actually their turn to start debugging, many people will find that the situation is full of problems. The steering gear has obviously been given the corresponding signal, but it either has no response and remains stationary, or it is turning in the wrong direction, completely inconsistent with expectations.
In fact, as long as you understand the principles behind the forward and reverse rotation of the steering gear, you will be able to control the precise movements of equipment such as robotic arms, cars, or model aircraft with ease. Based on my own experience accumulated from working on related projects in the past few years, I will conduct a detailed disassembly for you, starting from the core PWM signal, to the selection of theservoand subsequent maintenance, to make everything clear.
The forward and reverse rotation of the steering gear is achieved by the cooperation of its internal motor and gear set. Among them, the motor is a DC motor, and its forward and reverse rotation is determined by the direction of the current. However, ordinary motors cannot accurately stop at a specific angle. The steering gear is additionally equipped with a control board. When you send a pulse width signal to it, the control board will compare the current angle with the target angle, and then drive the motor to rotate forward or reverse until the gear set drives the output shaft to accurately align the corresponding position.
The motor and gear set inside the steering gear work together to achieve forward and reverse functions. This motor is a DC motor, and its forward and reverse rotation depends on the direction of the current. However, ordinary motors have shortcomings in accurately stopping at a certain angle. The steering gear has a unique advantage because of its control board. When given a pulse width signal, the control board will compare the current angle with the target angle, and then drive the motor to rotate forward or reverse until the gear set drives the output shaft to the designated position.
This process is actually a bit similar to setting the temperature of your home air conditioner. You set 26 degrees, and when the air conditioner detects that the room temperature is high, it starts cooling (equivalent to forward rotation), and when it is low, it starts heating (equivalent to reverse rotation). The same principle applies to the steering gear, except that it controls the angle, not the temperature.
The PWM signal can be called the command language of the steering gear. The standardservohas a specific control period of 20 milliseconds. Within this period, the high-level duration is from 0.5 milliseconds to 2.5 milliseconds, corresponding to the rotation range of the servo from 0 degrees to 180 degrees. When you want the servo to rotate forward, you only need to send a signal greater than 1.5 milliseconds; and if you want it to reverse, send a signal less than 1.5 milliseconds. For example, if you want the servo to rotate from 0 degrees to 180 degrees, directly give a 2.5 millisecond pulse signal, and the servo will automatically determine the direction of rotation based on the signal and accurately turn it.
But please note that the pulse range of different brands of servos may be different. The actual range of some 180-degree servos is 0.5 to 2.5 milliseconds, and some continuous rotation servos require you to adjust the pulse difference to change the speed and direction. You'd better first use an oscilloscope or debugging tool to measure the true response range of the servo in your hand.
On the robot joint, the forward and reverse rotation of the servo is the movement of arm bending and extension. For example, in a six-axis robotic arm, each joint requires precise forward and reverse rotation to send the end clamp to the designated position. If you use a servo to make a robot, you will find that the control logic is very simple: send an angle value, and the servo will handle forward, reverse, and stop on its own.
The application on model aircraft is also very typical. Turn the rudder to the left and the servo will rotate forward to a certain angle; turn the rudder to the right and it will reverse back. The most important thing is that the servo has its own position feedback, so you don’t have to worry about turning your head too much. If you are building a smart car, you can use a continuous rotating servo instead of an ordinary motor to achieve more precise steering and speed control.
When choosing a servo, first look at the torque and speed parameters. For example, if you want to make a robotic arm that grabs objects, and the load is large, you have to choose a high-torque servo with metal gears. The plastic gears are likely to directly sweep the teeth. The unit of torque is kg·cm, which means how heavy an object can be lifted 1 cm away from the axis. The greater the value, the greater the strength.
Then it depends on the angle range you want. Ordinary servos can only rotate 0 to 180 degrees or 0 to 270 degrees. If you need continuous rotation, you have to select "Continuous Rotation Servo". There is also a "digital servo" with faster response and more precise control, but it is also more expensive. Choose according to your application scenario, there is no need to blindly pursue expensive ones.
There are two main reasons for the servo to become stuck. On the one hand, the load is too large and exceeds the range that the steering gear can bear, causing the steering gear to jam; on the other hand, foreign objects are stuck in the gear, which hinders the normal operation of the steering gear. When encountering a jammed servo, you must first disconnect the power supply, then twist the output shaft by hand, and carefully observe whether the output shaft can rotate. If it cannot be tightened at all, it is likely that the internal gear has been damaged.
In addition to the above reasons, insufficient voltage is also a factor causing problems with the steering gear. The steering gear needs a stable power supply during operation. Especially when multiple servos are running at the same time, the voltage is prone to drop, which will cause the servos to shake back and forth, affecting their normal operation.
Signal interference will also cause the servo to rotate randomly. You can try adding a magnetic ring to the signal line, or separate the power supplies of the servo and motor driver board. If it is a program problem, check whether there are glitches in the PWM signal. It is best to use a logic analyzer to capture the waveform to see if the pulse width is stable.
Don't underestimate the servo wiring. I have seen many people plug in the signal cable backwards. As a result, the servo did not turn and they thought it was broken. Red is the positive pole of the power supply, brown or black is the negative pole, and orange or white is the signal wire. This order is basically an industry standard, and you won't go wrong if you confirm it.
It is also necessary to "angle reset" the steering gear regularly. Using a program to let the servo go back and forth from 0 degrees to 180 degrees several times can help the gear set wear evenly and avoid dead zones when working at one angle for a long time. If you are using a metal gear servo, occasionally adding some special lubricating oil can extend its life a lot.
What troublesome problems have you encountered when using servos to make products? Is it signal interference or the mechanical structure is stuck? Welcome to leave a message in the comment area and let’s exchange solutions together. If you think this article is helpful to you, don’t forget to like it, save it, and forward it to your friends who are also playing with the servo.
Update Time：2026-03-21
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