Animated Video Explaining The Working Principle Of Aircraft Steering Gear, A 3D Demonstration That Is Easy To Understand At A Glance

Hey, have you ever encountered this situation - the product design drawings are clearly drawn, but when it comes toservoselection or debugging, it gets stuck, and you always wonder: How does this thing work? Especially for those who want to make some innovative products on their own, theservomay look small, but there are really many tricks inside. Today we will put aside those obscure engineering drawings and use the most straightforward way to explain to you the working principle of this "small size, high energy" steering gear.

Why does theservoturn accurately but the motor keeps turning?

The ordinary DC motors we usually come into contact with only whir and turn when the power is turned on, and it is basically useless to stop them at a precise position. But the steering gear is different. There is actually a "small team" working inside it. You can think of it as an extremely obedient soldier. After receiving the order to "turn left 45 degrees", he must execute it to the letter and never be sloppy.

The secret of this accuracy lies in its internal closed-loop control system. The motor itself is always rotating, but the steering gear has the addition of controllers, potentiometers and gear sets. The potentiometer is like a real-time monitoring sensor, reporting to the controller "which position it is now at" at any time. The controller then compares the command position with the actual position. If there is a deviation, it immediately adjusts the motor direction until the position is accurately aligned.

What is the difference between aircraft servos and ordinary servos?

When we play model airplanes or make small robots, the servos we use only weigh a few grams to dozens of grams. But if you look at a real airplane, the steering gear on it is a "powerful man." When an airplane is in the air, the impact force of the airflow on the rudder surface is huge. It takes a lot of effort to move the rudder and elevator.

Therefore, the first requirements for aircraft servos, especially those in fly-by-wire flight control systems, arestrong strength, fast response, and extremely high reliability. It usually uses hydraulic or more advanced electrohydrostatic actuator (EHA) to convert electrical energy into hydraulic energy, and then uses hydraulic oil to push the piston to generate huge thrust. Moreover, aircraft generally have three or even four sets of redundant systems. If one system fails, the spare one will be immediately put on top. No jamming or failure is allowed.

How to choose the servo suitable for my product

Choosing a servo is like buying shoes, the fit is most important. Don't look at others who use high-torque ones, but you follow suit and buy them, only to find out after installing them that the product doesn't have enough space or the cost exceeds the standard. The first step is to figure out how much torque your mechanism needs. For example, if you want to lift a robotic arm, you have to calculate the arm length, weight and required speed, and leave a certain margin.

️Thekey is to look at these three points :

1. Torque: The unit is usually kg·cm, which means how many kilograms of weight can be lifted on a 1 cm long rocker arm. The larger the value, the greater the strength.

2. Speed: The unit is sec/60°, which is how many seconds it takes to turn 60 degrees. The faster the speed, the more responsive it is.

3. Size and weight: Check how much space is reserved for your product, and don’t buy it if you can’t fit it in.

4. Control accuracy: Digital servos have higher precision and faster response than analog servos. You can buy digital ones if you don’t want to spend money.

How to solve the problem of servo vibration and noise

I happily installed the servo and turned on the power, but it kept buzzing or shaking like I had Parkinson's disease. Isn't it really annoying? Most of this problem lies in the power supply and control signals. The current when the servo is started and blocked is very large. If the output power of your power supply is not enough, as soon as the voltage is pulled down, the controller inside the servo will be confused, causing jitter.

Another common cause is control signal interference. If you are using a microcontroller for PWM wave control, check whether the signal line is too long or tied together with a high-current power line. It is recommended to provide separate power supply to the servo, and the "ground" of the control signal should be shared with the "ground" of the power supply. Sometimes, the potentiometer of the servo itself is worn out, which can also cause vibration. In this case, you may have to consider replacing the servo.

What's the deal with the internal gears of the steering gear?

The bunch of small gears in the steering gear may seem inconspicuous, but they are actually the key to determining the life and accuracy of the steering gear. Most servos use plastic gears, mainly nylon. The advantages are low cost, light weight, and if they get stuck, they can break down first, protecting the motor and control circuit behind them. This is called "sacrificial protection."

But in situations where strength and precision are required, for example, if your product is a bionic robot that has to crawl and jump on the ground every day, it is best to choose a metal gear servo. Metal gears are more wear-resistant, stronger and can withstand greater impacts. However, once the metal gear gets stuck, it may directly damage the motor. In addition, the meshing clearance of the gear is also critical. If the clearance is large, the servo will be a little loose near the neutral position, which will affect the positioning accuracy.

How to understand the control signal waveform of the steering gear

If you are a maker who needs to write your own code to control the servo, then understanding the control signals is a basic skill. The most common servo control is PWM wave, which is square wave. There are three key elements in this signal: period, high level time and low level time. For standard servos, the period is fixed at 20 milliseconds, which is a frequency of 50Hz.

What really determines where the servo will turn isthe duration of the high level. Usually, a high level of 1 millisecond corresponds to the servo turning to the far left (such as 0 degrees), 1.5 milliseconds corresponds to the middle (90 degrees), and 2 milliseconds corresponds to the far right (180 degrees). You only need to generate a square wave with a period of 20 milliseconds and a high-level time varying between 1 and 2 milliseconds on your microcontroller, and you can accurately control the angle of the servo. Nowadays, many digital servos are more adaptable to signals, but if you understand this basic principle, debugging will be much easier.

Okay, let’s stop talking about the aircraft steering gear and the working principles behind it today. Let's talk from "why the conversion is accurate" to "how to choose and how to repair". I hope it will inspire you a little bit to tinker with your own new products. If you want to learn more about a specific type of steering gear, you can always search the official website of the relevant company, where you will find more detailed technical information.

Finally, I would like to ask you, what is the most troublesome steering gear problem you encountered in the process of making products? Is it because I am not sure about the model selection, or is there always bugs in debugging? Come and chat in the comment area. If you find the article useful, don’t forget to like and share it so that more friends can see it!