TECHNICAL SUPPORT
Published 2026-04-30
For common steering gear models, this article systematically sorts out their core differences. This difference covers key technical parameters such as structure type, control method, torque speed, size interface, etc., so as to help readers quickly grasp the key points of selection. The content of the article is based on common industry standards and does not involve specific brands. It only uses typical technical parameters and common application scenarios as examples to ensure that the information is universally applicable and authoritative.
Before starting to select a model, be sure to clearly define your application scenarios, such as model aircraft, robots, and industrial equipment, as well as core performance requirements, such as torque, speed, and accuracy, which will have a direct impact on model selection.
There are differences in steering gear models. These differences are mainly based on the following three dimensions. When you can understand these dimensions, you can complete 90% of the selection decisions.
Core conclusion: For entry-level amateurs, choose analog servos, and for high accuracy/response requirements, choose digital servos.
Standard PWM servo(most common models):
The signal line is single, and the pulse width range is generally 500μs to 2500μs. This range corresponds to 0 degrees to 180 degrees.。
Each servo needs to have an exclusive PWM interface
The control method is that the pulse width, whose unit is microseconds, is equal to 500 plus the angle divided by 180, multiplied by 2000.
Applicable: simple control system (Arduino, Raspberry Pi, receiver)
Serial bus servo(Intelligent steering gear):
Communicates via RS485, TTL or CAN bus
Multiple servos can be connected in series by sharing two lines (data + power)
Can return angle, temperature, voltage, load and other status
Support position, speed, current multiple closed-loop control
Applicable to: complex robots (bipods, robotic arms, multi-degree-of-freedom platforms)
Core conclusion: 5 servos or if status feedback is required, bus servos must be used.
There are usually common rules in naming servo gear models. The numbers are used to represent the representativeness of the item. Is it the unit of weight of the item in grams or the reference value of torque?. Take the typical rectangular plastic servo as an example:
The core conclusion is that the torque is equal to 0.5 times the moment arm. The unit of the moment arm is centimeters, and then multiplied by the load. The unit of the load is grams. After actual measurement, a 50% margin needs to be reserved.
The golden indicator for steering gear selection is torque. The calculation formula is: the required torque in kg·cm is equal to the load weight in kg multiplied by the length of the arm in cm multiplied by the safety factor and the safety factor must be greater than or equal to 1.5.
Among them, the standard working voltage is in the range of 4.8V to 6.0V, which is the most common situation. The 4.8V is the result obtained by 4 AA batteries, and the 6.0V is achieved by 2S lithium iron phosphate or 5 nickel metal hydride batteries.。
That thing called a high-voltage servo has a voltage range of 6.0V to 8.4V. It can be directly compatible with 2S lithium polymer batteries and does not require BEC to perform a voltage reduction operation. That's it.
The signal level here is that most of them are in a state where 3.3V and 5V are compatible with each other. This state belongs to the TTL level category. However, there are some industrial servos that require a level above 5V.
Overpressure is prohibited: Exceeding the rated voltage by 10% may burn the drive board and motor.
Core conclusion: Metal gears are the only choice for loads above 10kg·cm.
Standard 0-180 degrees: The most common, corresponding to pulse width 500-2500μs
0-270 degrees: Special potentiometer version, used for large-angle joints of robotic arms
continuous rotation: Remove the potentiometer or special program, it is actually a reduction motor + ESC
360 degree limit: Rare, used for pan/tilt and other scenes that require full rotation
Important reminder: Most of the so-called "360-degree servos" on the market are of the continuous rotation type. They have no way to position the angle and can only control the speed and direction.
Step 1: Determine whether angle positioning is required? ├─ Need precise angle → Standard 0-180 servo └─ Only rotation or speed → Continuous rotation of servo Step 2: Determine the number of servos? ├─ 1-4 → PWM servos (lowest cost) ├─ 5-10 → Recommended bus servos (simplified wiring) └─ >10 → Bus servos are required (otherwise IO and power supply cannot be managed) Step 3: Calculate the required torque Formula: Torque (kg·cm) = Load (g) × Moment arm (cm) / 1000 × 1.5 (safety factor) Example: 500g weight, force arm 5cm → 500×5/1000×1.5 = 3.75kg·cm → choose 5kg·cm or more. Step 4: Match the size and weight. Check the installation space (length × width × height), common sizes: 23×12×22mm (9g level), 40×20×38mm (35g level) Step 5: Confirm the control signal Receiver/Arduino/Raspberry Pi (PWM) → Standard PWM servo Microcontroller serial port/CAN bus → Intelligent bus servo The robot needs angle feedback → A bus servo or a PWM servo with feedback is required (three wires + feedback line)Q1: Can analog servos and digital servos be mixed?
A: It works.However, digital servos require controllers to support higher refresh rates. This refresh rate must be greater than or equal to 300Hz. Otherwise, its performance cannot be demonstrated, and analog servos cannot use high-frequency signals.。
Q2: How to judge whether the servo has been burned out?
Firstly, after the power is turned on, there is no self-test action. Secondly, when turning it manually, the resistance is quite large. Thirdly, the casing heats up significantly. Fourthly, it makes a buzzing sound but does not turn, which indicates that it is damaged.
Q3: Why is the servo vibrating out of control?
First check whether the power supply voltage and current are insufficient, secondly check whether the contact of the signal line is good, and finally check whether the potentiometer is worn or whether the program pulse is unstable.
Q4: Can the 9g servo be changed to continuous rotation?
A: Yes. Cut off the limit protrusion of the potentiometer and fix the midpoint of the potentiometer. However, the angle positioning will be lost and the speed direction can only be controlled.
Q5: How to set the ID of the bus servo?
A: Use the host computer software or serial port instructions to set it up. The default ID when leaving the factory is 1. When multiple machines are connected in parallel, each ID must be unique.
Q6: How to convert torque kg·cm and N·m?
A: 1 kilogram centimeter is equal to 0.098 Newton meters, which is approximately equal to 0.1 Newton meters. 5 kilograms centimeters is about 0.5 Newton meters. When purchasing, choose the data with the same unit according to industry habits.
The response time of digital servos is about one-tenth that of analog servos, but attention should be paid to controller signal frequency matching. The article writing prompts indicate that in this case, control accuracy is directly related to response speed.
Core point of view: The difference in steering gear models is concentrated in the dimension of structure, which is divided into two types: analog and digital. It is also reflected in the control aspect, including PWM and bus. In addition, torque size is also a dimension.. In each dimension, there are clear applicable boundaries. If there is an error in selection, it will lead to control failure or mechanical damage.
Suggestions for action：
1. Calculate your load torque immediately: Use a vernier caliper to measure the length of the power arm, use an electronic scale to weigh the load, and apply the formula load (kg) times the moment arm (cm) and then multiply by 1.5.
2. Turn on the caliper to measure the installation space. There are no less than three sizes to choose from, such as 25g, 35g, and 45g, to avoid the situation that it cannot be installed.
3. Confirm your controller interface: count the number of PWM available,
4. Leave a 50% torque margin. The measured torque is often 10 to 20% lower than the nominal, especially for lower-priced servos.
5. Prioritize metal gears: Once the torque requirement exceeds 5kg·cm, it must be replaced with metal gears, otherwise the plastic teeth will sweep during the first impact.
The prompt when writing this article is: after completing the selection operation, please perform a power-on test to verify whether there is no abnormal heating phenomenon when the servo is in the neutral state. After 10 minutes of trial operation with load, the outer shell temperature should be lower than 50°C.
The content presented above covers a complete set of knowledge system for differentiating steering gear models. Operating according to this guide can ensure that the correct model is selected and a successful result is achieved the first time.
Update Time：2026-04-30
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