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Published 2026-04-13
This guide provides a clear, practical breakdown ofservomotor specifications and model numbering systems. Understanding these parameters is essential for selecting the correctservofor robotics, RC vehicles, or industrial automation. The three most critical specifications you must evaluate first aretorque, speed, andphysical size. This article will explain how to interpret these and other key specs, decode common model number patterns, and apply a step-by-step selection process using real-world examples.
Everyservo’s performance is defined by a set of measurable parameters. Focus on these three first, as they directly determine if a servo will work for your application.
What it is: The maximum rotational force the servo can exert when its output shaft is stalled (not moving). Measured inkg·cm(kilogram-force per centimeter) oroz·in(ounce-force per inch).
How to interpret: A servo rated at 5 kg·cm can hold a 5 kg weight suspended 1 cm from the shaft’s center. For a 10 cm lever arm, the effective force drops to 0.5 kg.
Real-world example: A standard robotic arm joint lifting a 300g payload at a 5 cm distance requires at least 1.5 kg·cm of torque (0.3 kg × 5 cm = 1.5 kg·cm). A safe choice would be a 3-4 kg·cm servo.
Selection rule: Always choose a servo with20-30% higher torquethan your calculated maximum load to account for dynamic forces and friction.
What it is: The time required for the output shaft to rotate a specified angle (usually 60°), measured inseconds/60°.
How to interpret: A speed rating of 0.15 sec/60° means it takes 0.15 seconds to move 60 degrees. Lower numbers are faster.
Real-world example: For a pan-tilt camera mount that needs to track moving objects, a speed of 0.10 sec/60° or faster is ideal. For a solar panel positioner that adjusts once per hour, 0.25 sec/60° is perfectly acceptable.
Torque-speed trade-off: Within the same servo series, faster speed almost always means lower torque, and vice versa.
Servo sizes follow de facto standards. Use these common cases as references:
Key insight: Physical size determines not just fit, but also mounting hole pattern (e.g., standard “Futaba” pattern has 48mm spacing for standard servos). Always verify your mounting bracket dimensions.
Plastic gears: Lower cost, quieter, but wear faster under load. Suitable for light-duty applications like educational robots.
Metal gears: Higher cost, louder,but much more durable. Mandatory for any application with impact loads or continuous high torque (e.g., robot legs, RC steering).
Real-world case: A hobbyist built a robotic arm using plastic-geared servos. After 200 lift cycles, the gears stripped. Replacing them with metal-geared servos solved the problem permanently.
Standard protocol: 50 Hz signal (period = 20 ms). Pulse width typically ranges from 1 ms to 2 ms.
1.0 ms pulse → 0° position
1.5 ms pulse → 90° (neutral)
2.0 ms pulse → 180°
Important variation: Some servos have extended ranges (0°-270° or continuous rotation). Verify the datasheet before connecting.
Verification: If your servo does not respond to standard PWM, it may be a 360° continuous rotation servo (discussed below).
Standard angular rotation: 180° (most common for robotics and RC surfaces).
Extended rotation: 270° (used for specialized pan mechanisms).
Continuous rotation: No endpoint. The servo rotates continuously with speed proportional to pulse width deviation from 1.5 ms. Used for robot wheels.
Standard range: 4.8V – 6.0V (common for 4-cell or 5-cell NiMH batteries).
High-voltage (HV) servos: Rated for 6.0V – 8.4V (direct 2S LiPo compatibility).
Critical rule: Never exceed the maximum rated voltage. A servo rated for 6.0V connected to a 7.4V LiPo will overheat and fail within minutes.
Performance note: Torque and speed increase with voltage. A servo rated 5 kg·cm at 4.8V may deliver 6.5 kg·cm at 6.0V.
Most servo manufacturers follow a logical but unstandardized naming convention. Once you understand the pattern, you can extract key specs without a datasheet.
[Size/Series][Gear Type][Torque/Speed Code][Rotation Type]
Examples decoded:
Digits “9xx” or “99x” : Usually indicates a standard-size servo with torque between 9-15 kg·cm (e.g., 995, 996).
Digits “90” or “9” : Typically micro servos (SG90, MG90).
Prefix “DS” : Digital servo (faster response, higher holding power).
Prefix “HS” : High-speed or high-torque series (varies by brand).
Suffix “BB” : Ball bearing supported output shaft (smoother rotation, longer life).
Practical takeaway: When comparing two servos from the same series, the model number often increases with torque. For example, 3218 → 3225 → 3235 indicates a progression from 18 kg·cm to 25 kg·cm to 35 kg·cm.
Follow these five steps in order. Do not skip to torque or size first without defining the application.
Question: What is the servo moving? How often? Under what load?
Case A – Robot arm elbow joint: Moves a 200g forearm + 100g gripper at 8cm distance. Peak torque = (0.3 kg × 8 cm) = 2.4 kg·cm. Add 30% safety margin = 3.1 kg·cm minimum.
Case B – RC car steering: Wheels on high-traction carpet create high impact loads. Recommended torque = 7-10 kg·cm for 1/10 scale.
Case A (robot arm): Speed is secondary; 0.20 sec/60° is fine.
Case B (RC car): Speed is critical; target 0.12 sec/60° or faster for responsive steering.
Measure your available mounting space. Standard servos need ~40x20mm footprint and 38mm depth.
Common issue: Users buy a standard servo but have a micro servo mount. Always check the bracket’s hole spacing.
From the table in Section 1.3:
3.1 kg·cm requirement → Micro or sub-micro servo (e.g., 2.5-4 kg·cm class).
7-10 kg·cm requirement → Standard servo.
Gear type: Metal for Case B (impacts). Plastic acceptable for Case A (smooth motion).
Voltage: Ensure your existing power supply matches the servo’s operating voltage range.
Analog servo: Receives PWM signal 50 times per second. Motor is powered only during the pulse. Simpler, lower cost, but lower holding power.
Digital servo: Receives same PWM signal but processes it at 300+ times per second. Motor receives near-continuous power. Benefits:
Faster response time (0-5 ms vs 10-15 ms)
Higher holding torque at neutral
Smoother motion at low speeds
Draws more current (important for battery life)
Selection rule: For precision applications (robot arms, camera gimbals, CNC), choose digital. For basic RC surfaces (throttle, simple flaps), analog is sufficient.
> Torque determines if it can move. Speed determines how fast. Size determines if it fits. Metal gears determine if it survives.
1. Calculate your actual required torque using the formula:
Torque (kg·cm) = Weight (kg) × Arm Length (cm) × 1.3 (safety factor)
2. Write down three constraints in this order: torque needed → speed needed → maximum dimensions.
3. Look up servos that meet or exceed the torque requirement first. Then filter by speed, then by size.
4. Check the gear type: If the application has any impact or shock load, metal gears are not optional.
5. Verify voltage compatibility with your existing power source. Do not assume.
6. Test with a servo tester before integrating into your final assembly. This catches wiring or signal issues early.
[ ] Torque rating is at least 30% above calculated maximum load
[ ] Speed meets or exceeds application requirement
[ ] Physical dimensions fit within mounting area (check hole spacing)
[ ] Gear type matches load profile (metal for impact/continuous high torque)
[ ] Operating voltage matches available power supply
[ ] Rotation angle (180°, 270°, or continuous) is correct for the task
[ ] Digital vs. analog choice aligns with precision needs
By following this specification-driven selection process and decoding model numbers systematically, you will consistently choose the correct servo for any application – from micro robotic fingers to industrial-grade actuators. Always prioritize torque and gear type first, then validate speed and voltage. This approach eliminates the most common failure modes and ensures reliable, long-term operation.
Update Time：2026-04-13
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