P
Closed-loop position control
Feedback allows the robot to correct motion errors rather than assuming that the commanded movement occurred.
Robotics Motion-Control Engineering Guide
Servo Motors for Robotics: Control, Sizing and Selection
An engineering guide to servo motors, drives, encoders and closed-loop robotic motion
Servo motors provide controlled torque, speed and position inside robotic motion systems.
A complete servo axis combines a motor, feedback device, servo drive, controller and mechanical load. This guide explains how those elements work together and what engineers should evaluate before selecting a servo motor for a robot.
What Is a Servo Motor?
A servo motor is a motor used as part of a closed-loop motion-control system.
The system compares a commanded position, speed or torque with measured feedback and continuously adjusts the motor current to reduce the difference.
In industrial robotics, the term “servo motor” normally refers to a motor designed to operate with a compatible servo drive and feedback device. The complete servo system also includes control electronics, communication, power conversion and the mechanical load.
In summary
- The motor converts electrical energy into mechanical torque.
- The encoder measures the actual motor or joint state.
- The servo drive controls motor current and motion.
- The controller generates position, velocity or torque commands.
- The feedback loop corrects the difference between command and response.
- The transmission and load determine the motor’s real operating requirement.
remains the published international robotics-vocabulary standard. treats an adjustable-speed power-drive system as including power conversion, drive control and one or more motors—motor and drive performance should be considered as a system.
What Is the Difference Between a Motor, Servo Motor and Servo System?
| Term | Definition | Typical contents |
|---|---|---|
| Electric motor | Converts electrical energy into mechanical motion | Rotor, stator, shaft and bearings |
| Servo motor | Motor intended for controlled closed-loop motion | Motor plus compatible feedback interface; brake may be optional |
| Servo drive | Supplies controlled electrical power to the motor | Power electronics, current control, feedback processing and communications |
| Servo controller | Generates motion commands | Position, velocity, torque, trajectory or coordinated-axis control |
| Servo system | Complete closed-loop axis | Controller, drive, motor, feedback, transmission and load |
| Robot actuator | Complete motion-producing mechanical module | Servo motor, drive, reducer, encoder, brake, bearings and housing |
A servo motor is not automatically a complete actuator. The motor generates shaft torque. A robot actuator may additionally contain the reducer, output bearing, brake, joint housing, torque sensor and drive electronics required to deliver usable motion to the robot structure. See complete robot actuator architecture.
How Does a Servo Motor Work?
- The robot controller calculates the required position, velocity or torque.
- The servo drive receives the command and calculates the current required from the motor.
- The drive switches electrical power into the motor windings.
- Electromagnetic interaction inside the motor produces shaft torque.
- The motor moves the transmission, robot joint or direct-drive load.
- An encoder or other feedback sensor measures the actual motion.
- The drive or controller compares actual motion with the command.
- The system adjusts motor current continuously to reduce the control error.
Control-loop hierarchy
- Command
- Position loop
- Velocity loop
- Current / torque loop
- Motor and mechanical load
Feedback → Control loops
The feedback loop is what distinguishes servo control from uncontrolled motor operation. The quality of motion depends not only on encoder resolution, but also on control-loop tuning, mechanical stiffness, friction, backlash, motor inertia, load inertia and signal latency.
What Components Make Up a Servo System?
| Component | Function | Important parameters |
|---|---|---|
| Servo motor | Generates shaft torque and speed | Continuous torque, peak torque, rated speed, maximum speed and inertia |
| Servo drive | Controls current and motor motion | Voltage class, current, control bandwidth, feedback support and safety functions |
| Encoder | Measures angular or linear motion | Type, resolution, accuracy, latency and absolute/multiturn capability |
| Motion controller | Generates axis commands and trajectories | Cycle time, interpolation, synchronization and communication |
| Holding brake | Holds the stopped axis under defined conditions | Holding torque, release time, voltage and lifecycle |
| Transmission | Changes speed, torque or motion form | Ratio, efficiency, stiffness, backlash and life |
| Mechanical load | Defines the actual motion requirement | Mass, inertia, friction, external forces and motion profile |
| Cabling | Carries power, feedback, brake and communication | Current rating, shielding, flex life and connector compatibility |
| Software | Configures, tunes and diagnoses the axis | Tools, firmware, APIs, licences and update policy |
Why Do Robots Use Servo Motors?
T
Controlled torque and speed
The drive can regulate motor current, velocity and position across different parts of the robot’s motion cycle.
D
High dynamic response
Servo systems can produce short-duration peak torque for acceleration and deceleration while operating within a lower continuous thermal limit.
M
Coordinated multi-axis motion
Robot controllers can synchronize several servo axes to follow a trajectory through space.
V
Diagnostic visibility
Servo systems can expose position, speed, current, following error, temperature and fault information.
S
Integration with safety functions
Suitable drives and encoders can support defined safety-related drive functions where the complete system is designed and validated accordingly.
addresses functional-safety requirements for safety-related power-drive systems. provides additional requirements for encoders when safety-related encoder functions are claimed. These standards apply only where the corresponding safety scope applies.
What Types of Servo Motors Are Used in Robotics?
Servo motors can be classified using more than one dimension. These categories overlap—a motor can simultaneously be a brushless permanent-magnet, rotary, low-inertia, frameless servo motor.
By electromagnetic construction
- Permanent-magnet synchronous or brushless AC servo motor
- Brushed DC servo motor
- Asynchronous or induction servo motor
- Switched-reluctance or specialist motor architecture
By output geometry
- Rotary servo motor
- Linear servo motor
- Direct-drive torque motor
- Frameless or kit motor
By rotor inertia
- Low-inertia servo motor
- Medium-inertia servo motor
- High-inertia servo motor
Brushless Servo Motors
Most modern industrial servo motors use a brushless permanent-magnet architecture. Electronic commutation replaces the mechanical brushes used in a brushed DC motor. Rotor position feedback allows the drive to control phase current and generate the required torque.
Typical advantages: No brush wear, high torque density, high speed capability, low rotor inertia options, accurate electronic commutation and strong compatibility with digital servo drives.
Primary constraints: Drive and encoder compatibility, magnet-temperature limits, thermal management, cable and connector requirements, control tuning and supply-voltage dependence.
Do not state that every brushless motor is a servo motor. It becomes part of a servo system only when integrated into suitable closed-loop control.
Brushed DC Servo Motors
A brushed DC servo motor uses mechanical brushes and a commutator to switch current through the rotor windings. It can be used in closed-loop servo control and may provide simple torque control, but brush and commutator wear create maintenance and lifecycle considerations.
Appropriate contexts include legacy automation equipment, lower-power mechanisms, cost-sensitive specialist systems and applications with established brushed-drive architecture. Main limitations include brush wear, electrical noise, maintenance, speed and thermal limits.
Direct-Drive Torque Motors
A direct-drive torque motor connects the motor output directly to the robot joint or load without a conventional high-ratio gearbox. This can reduce transmission backlash, friction and reflected transmission inertia, but requires the motor to generate the required joint torque directly.
Main advantages: Low mechanical backlash, high backdrivability, reduced transmission wear, high control transparency and fewer transmission components.
Main trade-offs: Larger motor diameter, higher current demand, greater cooling requirement, higher motor mass and potentially more demanding drive electronics.
Linear Servo Motors
A linear servo motor produces direct translational force without converting rotary motion through a screw, belt or gearbox. The motor normally requires a separate linear guide, feedback scale and mechanical structure to carry non-axial loads.
Typical applications include Cartesian robots, high-speed positioning stages, semiconductor and inspection equipment, precision gantries and pick-and-place mechanisms. Main parameters include continuous force, peak force, maximum velocity, acceleration, force ripple, travel, feedback resolution, thermal load and air gap.
Servo Motor vs Stepper Motor: What Is the Difference?
| Dimension | Servo motor system | Stepper motor system |
|---|---|---|
| Control model | Normally closed loop | May be open or closed loop |
| Feedback | Encoder or resolver normally present | Optional in conventional systems |
| Torque at higher speed | Generally maintained over a broader speed range | Typically declines substantially with speed |
| Position loss | Detected through feedback | May remain undetected in open-loop systems |
| Tuning | Required | Often simpler |
| Cost and complexity | Higher | Often lower |
| Standstill behaviour | Controlled by drive and brake design | Can hold through phase current |
| Best fit | Dynamic, high-performance or variable-load motion | Simpler, lower-cost or lower-speed positioning |
A servo motor is not universally better than a stepper motor. Servo systems are generally preferred when the application requires high speed, dynamic acceleration, load variation, feedback and error correction. Stepper systems may remain appropriate where motion is predictable and lower cost or simplicity matters more than dynamic performance.
Servo Motor vs DC Motor: Are They the Same?
A DC motor describes an electrical motor category. A servo motor describes a motor’s role inside a controlled servo system. A brushed DC motor can be used as a servo motor when it operates with feedback and closed-loop control. Many modern industrial servo motors, however, use brushless permanent-magnet construction driven by an electronic servo drive.
| Question | DC motor | Servo motor |
|---|---|---|
| Does the term define motor construction? | Yes | Not necessarily |
| Is feedback required by the term? | No | Normally yes in industrial usage |
| Is a compatible drive needed? | Depends on application | Yes |
| Can it control precise position? | Only with suitable control and feedback | Designed for closed-loop control |
| Can it be brushed or brushless? | Yes | Yes |
Is a Servo Motor the Same as a Robot Actuator?
No. A servo motor generates controlled shaft torque. A robot actuator is the larger motion-producing assembly that transfers that torque to the robot. A complete joint actuator may include the servo motor, servo drive, reducer, encoders, brake, torque sensor, bearings, housing and output flange.
See robot actuator architecture and harmonic reducer integration for joint-level design context.
What Are the Most Important Servo-Motor Specifications?
Torque
- Continuous stall torque, continuous torque at rated speed
- Peak torque, peak duration, torque constant, cogging torque
- Holding requirement
Speed
- Rated speed, maximum speed, base speed
- Overspeed limit, speed at required torque
Power and electrical
- Rated power, supply-voltage class
- Continuous and peak current
- Back-EMF constant, phase resistance and inductance
Mechanical
- Rotor inertia, shaft diameter, radial and axial load
- Mass, frame size, mounting flange
Feedback
- Encoder type, resolution, absolute or incremental
- Single-turn or multiturn capability, accuracy, communication interface
Thermal and lifecycle
- Thermal resistance, maximum winding temperature
- Ambient-temperature rating, cooling method
- Bearing life, brake life, ingress protection, drive compatibility
How Should a Servo Motor Be Selected for a Robot?
Servo-motor selection must be based on the complete torque-speed cycle, reflected inertia, transmission, thermal conditions, feedback requirements and drive compatibility—not rated power or peak torque alone.
1
Define the mechanical load
- Payload, link mass, moment arm, external process force
- Gravity direction, friction, transmission, counterbalance
2
Define the motion profile
- Position range, maximum speed, acceleration, deceleration
- Cycle time, reversals, holding periods, emergency-stop profile
3
Calculate load torque
- T = J × α for acceleration; T = F × r for static force
- Include gravity, inertial, process, friction and margin torques
4
Calculate required speed
- Motor speed = Output speed × Reduction ratio
- Must remain within motor-and-drive torque-speed envelope
5
Check peak torque
- Acceleration, deceleration, load changes
- Disturbance rejection and short process events
6
Check continuous and RMS torque
- Trms = √[(T₁²t₁ + … + Tn²tn) / total cycle time]
- Must remain within continuous thermal limit
7
Check motor and load inertia
- Motor rotor, load, transmission and reflected load inertia
- Permitted tuning range and mechanical resonance
8
Select the transmission ratio
- Affects motor torque, speed, reflected inertia, stiffness
- Backdrivability, friction and control bandwidth
9
Check drive compatibility
- Supply voltage, continuous and peak current
- Feedback support, brake output, control modes, protocol, safety
10
Check thermal conditions
- Ambient temperature, mounting, heat-conduction path
- Enclosure, cooling, duty cycle, continuous current
11
Check physical integration
- Frame size, mass, shaft, flange, connector orientation
- Cable routing, brake, ingress protection, service access
12
Validate the real cycle
- Actual torque-speed trajectory, acceleration, dwell periods
- Actual ambient, mounting, transmission, control and load uncertainty
How Are Servo-Motor Torque, Speed and Power Related?
Mechanical rotary power: P = T × ω
Where P = power in watts, T = torque in newton-metres, ω = angular velocity in radians per second.
Conversion from rotational speed: ω = 2πn / 60 where n is revolutions per minute.
A motor does not normally provide its maximum torque at every speed. Available torque is limited by motor current at lower speed and increasingly by supply voltage, back EMF, drive capability and thermal conditions as speed increases.
Performance is a matched motor-and-drive property under stated test conditions
What Is the Difference Between Continuous, Peak and RMS Torque?
| Parameter | Meaning |
|---|---|
| Continuous torque | Torque that can be sustained under the defined thermal conditions |
| Continuous stall torque | Continuous torque at zero speed under specified cooling and ambient conditions |
| Peak torque | Short-duration torque limited by current, magnetic and mechanical constraints |
| RMS torque | Effective torque across the complete repeating duty cycle |
| Holding torque | Torque required while the joint remains stationary |
| Brake holding torque | Load that the engaged holding brake can retain at rest |
Peak torque determines whether the motor can complete short acceleration or disturbance events. RMS and continuous torque determine whether it can repeat the cycle without exceeding its thermal limit.
Why Do Servo-Motor Test Conditions Matter?
Servo-motor torque ratings depend on the conditions under which heat can leave the motor. Ambient temperature, mounting plate, enclosure, airflow, drive pairing and winding-temperature limit can materially change the available continuous operating region.
Every published torque-speed curve should identify: motor model, servo-drive model, supply voltage, ambient temperature, motor mounting condition, cooling method, winding or case-temperature limit, continuous region, peak or intermittent region and permitted duty cycle.
Do not reproduce supplier curves without attribution or redraw them as if they were universal servo-motor behaviour.
Why Does Load Inertia Matter in Servo-Motor Selection?
Inertia determines how much torque is required to change rotational speed. A load with high inertia requires more acceleration and deceleration torque and can make the servo axis more difficult to tune.
For an ideal gearbox with reduction ratio N:
Reflected load inertia at the motor: Jreflected = Jload / N²
A higher reduction ratio can reduce the load inertia reflected to the motor, but it also raises motor speed and can add transmission friction, compliance and backlash. There is no universal ideal inertia ratio. The acceptable ratio depends on the motor, drive, control bandwidth, transmission and required motion.
How Should a Servo Motor Be Matched to a Harmonic Reducer?
Motor speed ≈ Joint output speed × Reduction ratio
Ideal motor torque ≈ Joint output torque / Reduction ratio
Correct for reducer efficiency, acceleration, reflected inertia, friction, preload, duty cycle and thermal limits.
| Interface | Question |
|---|---|
| Motor shaft ↔ reducer input | Are shaft, coupling, pilot and flange compatible? |
| Motor speed ↔ reducer limit | Does maximum motor speed remain inside the reducer limit? |
| Motor inertia ↔ control | Does the resulting joint support the required bandwidth? |
| Motor heat ↔ reducer | Will motor heat raise reducer or lubricant temperature? |
| Encoder ↔ joint accuracy | Is motor-side feedback sufficient, or is output feedback needed? |
| Brake ↔ joint load | Can the brake safely hold the axis under the defined condition? |
A suitable motor and a suitable reducer do not automatically create a suitable robot joint. The complete actuator must be evaluated for torque, speed, stiffness, backlash, thermal behaviour, output loading and control response. See harmonic reducers and robot actuators.
Does a Higher-Resolution Encoder Make a Servo Motor More Accurate?
Not automatically. Encoder resolution describes how finely the feedback device represents position. System accuracy also depends on encoder accuracy, mounting, control tuning, transmission error, backlash, stiffness, thermal drift and mechanical alignment.
| Term | Meaning |
|---|---|
| Encoder resolution | Number of distinguishable measurement increments |
| Encoder accuracy | Closeness of the measured angle to the true angle |
| Repeatability | Ability to return to the same position |
| Following error | Difference between commanded and measured position |
| Transmission error | Error introduced through the mechanical transmission |
| Output accuracy | Accuracy measured at the actual robot joint or tool |
A high-resolution motor encoder can improve control sensitivity while still failing to observe reducer lost motion or joint deflection. Output-side feedback may be required when the application must measure the actual joint output. See encoder and feedback selection.
What Is the Difference Between a Servo Drive and Servo Controller?
| Servo drive | Servo controller |
|---|---|
| Regulates motor current and lower-level motion loops | Generates axis commands and trajectories |
| Interfaces directly with the motor and encoder | Coordinates one or more axes |
| Executes current, velocity and often position control | Performs interpolation, kinematics and application logic |
| Handles motor commutation and protection | Communicates with robot, PLC or higher-level software |
| May provide safety-related drive functions | Coordinates system-level safety logic where designed |
In some products, drive and controller functions are combined in one device. The functional distinction remains useful because the drive controls motor power and feedback, while the controller determines what motion the axis should perform. See robot motion controllers.
Which Control Modes Can a Servo Motor Use?
- Current or torque control — controls motor current as a proxy for electromagnetic torque.
- Velocity control — controls shaft speed using encoder feedback.
- Position control — controls shaft or joint position through a closed feedback loop.
- Impedance control — controls the relationship between position, velocity and applied force or torque.
- Force or torque control — uses current estimation, a torque sensor or both to regulate interaction force.
Supporting a named control mode does not establish the achievable bandwidth, accuracy or stability. Performance depends on the motor, drive, feedback, mechanical structure, transmission and tuning.
What Does a Servo-Motor Brake Do?
A servo-motor brake is normally a holding brake. Its primary purpose is to hold a stationary motor shaft or robot axis after the drive has brought it to rest. It should not automatically be treated as a service brake for repeatedly stopping a moving load.
Confirm brake holding torque, release voltage, release and engagement time, maximum permitted speed at engagement, brake lifecycle, vertical-axis load, emergency behaviour, manual release and monitoring.
Manufacturer motor instructions state that optional holding brakes are designed to hold a shaft at zero speed and are not intended to stop a rotating shaft or act automatically as the safety device. For safety-related drive functions, use the applicable system-level framework——rather than assuming a motor brake alone provides safe motion control.
What Interfaces Must Be Defined for a Robot Servo Motor?
| Interface | Required information |
|---|---|
| Mechanical mounting | Flange, pilot, shaft, key, bolt pattern and tolerances |
| Load | Radial force, axial force, coupling load and transmission preload |
| Electrical power | Voltage, continuous current, peak current and connector |
| Feedback | Encoder protocol, resolution, accuracy and connector |
| Brake | Voltage, current, release timing and monitoring |
| Drive compatibility | Supported motor model, commutation and parameter set |
| Communication | EtherCAT, CAN, industrial Ethernet or vendor protocol |
| Control | Position, velocity, torque and synchronization requirements |
| Safety | STO and other required drive or encoder safety functions |
| Thermal | Ambient, mounting plate, enclosure, cooling and derating |
| Environment | IP rating, vibration, shock, contamination and corrosion |
| Lifecycle | Drive availability, encoder availability, firmware and spare parts |
covers electrical, thermal, fire, mechanical and energy hazards for adjustable-speed power-drive systems. applies where safety-related encoder performance is claimed.
Does Servo-Motor Accuracy Determine Robot Accuracy?
No. Servo-motor and encoder performance are only part of the robot’s total error chain. Robot accuracy can also be affected by reducer transmission error, joint stiffness, backlash, link deformation, temperature, calibration, controller compensation, payload and installation.
defines performance criteria and related test methods for manipulating industrial robots at the robot-system level. It should not be presented as a component-level servo-motor test standard.
How Should a Servo Motor and Drive System Be Tested?
Static motor characteristics
- Torque constant, resistance, inductance
- Encoder alignment, holding brake, shaft runout, insulation
Torque-speed performance
- Continuous and peak operating regions
- Rated and maximum speed, voltage and drive-current dependence
Dynamic performance
- Acceleration, settling time, tracking and following error
- Control bandwidth, reversal response, disturbance rejection
Thermal performance
- Continuous-cycle winding and case temperature
- Drive temperature, thermal equilibrium, cooling dependence, derating
Feedback performance
- Encoder accuracy, resolution, latency
- Absolute-position retention, multiturn behaviour, signal integrity
Mechanical and durability
- Vibration, noise, bearing load, shaft deflection
- Bearing life, cable flex life, brake cycles, thermal cycling, ingress protection
Evidence rule: Every performance claim should identify motor model, matched drive, supply voltage, ambient temperature, mounting condition, feedback configuration, control settings, mechanical load, test duration and measurement method.
Common Mistakes When Selecting Servo Motors for Robots
| Mistake | Likely consequence |
|---|---|
| Selecting by rated power alone | Torque or speed mismatch |
| Using peak torque as continuous torque | Overheating |
| Ignoring the complete duty cycle | Incorrect RMS torque calculation |
| Ignoring load inertia | Poor acceleration or unstable tuning |
| Treating encoder resolution as system accuracy | Overstated positioning capability |
| Selecting the motor without the drive | Incompatible or unavailable performance |
| Ignoring supply voltage | Reduced high-speed torque |
| Ignoring mounting and cooling | Continuous-torque derating |
| Ignoring reducer efficiency and stiffness | Incorrect joint performance |
| Assuming the brake stops moving loads | Brake damage or unsafe behaviour |
| Ignoring cable flex life | Intermittent field faults |
| Ignoring firmware and tuning tools | Integration and lifecycle dependency |
| Selecting prototype-only motors | Production or obsolescence exposure |
| Accepting non-comparable supplier curves | Invalid supplier comparison |
What Evidence Should a Servo-Motor Supplier Provide?
Product documentation
- Dimensioned drawing, winding and voltage class
- Continuous and peak torque, rated and maximum speed
- Rotor inertia, mass, radial and axial load limits
Motor-drive system evidence
- Approved drive combinations and torque-speed curves
- Supply-voltage conditions, continuous and peak current
- Control modes and communication interfaces
Thermal and feedback evidence
- Ambient conditions, mounting assumption, derating curves
- Encoder type, resolution, accuracy, protocol
- Safety certification where applicable
Manufacturing and lifecycle evidence
- Magnet and lamination sourcing, winding process, rotor balancing
- Encoder alignment, end-of-line testing, traceability
- Drive configuration tools, firmware ownership, end-of-life notification
Confirmed through primary documentation
Supplier-reported
Supported by independent test evidence
Not confirmed
Not disclosed
Sourcing Servo Motors for Robotics in China
China has broad manufacturing capability across motors, servo drives, encoders, power electronics, machining and integrated robot joints. The sourcing challenge is determining which elements the supplier actually designs and controls.
A company may manufacture the motor while purchasing the encoder and drive. Another may assemble a complete servo package from third-party components. An integrated robot-joint supplier may control the housing and mechanical integration but depend on outside firms for the motor, reducer or firmware.
Supplier evaluation should separate motor manufacturing, drive development, feedback ownership, system tuning and actuator integration. Classify suppliers as technology owners, motor manufacturers, drive manufacturers, motor-and-drive system suppliers, geared-servo suppliers, integrated-joint manufacturers, distributors, private-label suppliers or trading companies.
The presence of a motor, encoder and drive in one catalogue does not prove that the supplier owns or validates the complete servo system. Buyers should establish component ownership, motor-drive compatibility, test conditions, firmware support and lifecycle responsibility.
What Should Be Included in a Servo-Motor RFQ?
Robot and application context
- Robot category, application, joint or axis location
- Development stage, destination market
- Pilot quantity, expected annual volume, target production date
Motion profile and torque
- Maximum and average motor or output speed
- Acceleration, deceleration, cycle time, reversals
- Continuous, RMS, peak torque and peak duration
- Load inertia, transmission ratio and efficiency
Motor and feedback configuration
- Brushless, brushed, direct-drive or linear
- Voltage class, frame size, shaft, flange, mass limit
- Brake requirement, ingress rating, cooling
- Encoder type, resolution, accuracy, absolute or incremental
Drive, environment and lifecycle
- Continuous and peak current, supply voltage, regeneration
- STO or other required safety functions, configuration tools
- Ambient temperature, vibration, shock, humidity
- Expected life, bearing life, cable flex life, brake life
Required evidence
- Motor-and-drive torque-speed curve with continuous and peak definitions
- Thermal-test conditions, motor inertia, encoder documentation
- Drive compatibility, reliability evidence, manufacturing traceability
Frequently Asked Questions
What is a servo motor?
A servo motor is a motor used within a closed-loop motion-control system. Feedback measures the actual motion, and the servo drive adjusts motor current to follow the commanded position, speed or torque. See the definition section and parent robot components guide.
How does a servo motor work?
The controller sends a command to the servo drive. The drive powers the motor, the encoder measures the resulting motion, and the control loop corrects the difference between the commanded and measured state. See the eight-step operating sequence and control-loop hierarchy.
What is the difference between a servo motor and a normal motor?
A normal motor may run without precise feedback control. A servo motor is selected and configured to operate with a compatible drive, feedback device and closed-loop controller. The distinction is about system role, not motor construction alone. See the comparison table.
What is the difference between a servo motor and a servo drive?
The motor converts electrical power into mechanical torque. The servo drive controls the electrical power supplied to the motor and processes feedback to regulate motion. See drive vs controller for how these relate to the motion controller.
Why do robots use servo motors?
Robots use servo motors because they require coordinated control of position, speed and torque under changing loads. Feedback allows the system to measure and correct motion errors across dynamic motion cycles. See six engineering reasons.
What servo motors are used in robot arms?
Most industrial robot arms use brushless permanent-magnet servo motors, normally combined with reducers, encoders, drives and holding brakes. Direct-drive torque motors are used in some architectures. See robot actuator architecture and reducer matching.
Is a servo motor the same as an actuator?
No. The servo motor produces shaft torque. The actuator is the complete motion-producing assembly and may also contain a reducer, bearings, brake, feedback sensors, housing and electronics. See servo vs actuator.
What is the difference between a servo motor and a stepper motor?
Servo systems normally use closed-loop feedback and are suited to dynamic, variable-load motion. Stepper systems may be simpler and lower cost but can lose position without detection when operated open loop. See the comparison table.
What is servo-motor peak torque?
Peak torque is the short-duration torque available for events such as acceleration and deceleration. It cannot normally be sustained continuously without exceeding current or thermal limits. See continuous, peak and RMS torque.
How do I calculate servo-motor torque?
Calculate the torque required for gravity, acceleration, external loads and friction across the complete motion cycle. Use T = J × α for inertial torque and T = F × r for static force. Then account for transmission ratio, efficiency, RMS torque, peak torque and engineering margin. See the selection framework.
What is servo-motor inertia?
Servo-motor inertia is the rotational inertia of the motor rotor. It affects how quickly the motor can accelerate and how it interacts dynamically with the reflected load inertia. See load inertia and reflected inertia.
Does a higher-resolution encoder make a servo motor more accurate?
Not automatically. Resolution is only one part of accuracy. Mechanical alignment, encoder accuracy, transmission error, stiffness, backlash, temperature and control tuning also affect the output. See the encoder terminology table.
Does a servo-motor brake stop the motor?
A typical servo-motor brake is intended to hold an already stopped shaft. It should not be assumed to provide repeated dynamic stopping or complete safety functionality. See holding brakes and safety.
How do I choose a servo-motor supplier?
Compare the complete motor-and-drive system, torque-speed performance, thermal test conditions, feedback, manufacturing controls, software support and lifecycle evidence—not only motor power or catalogue torque. See the supplier evidence framework.
How do I source servo motors from China?
Define the motor, drive, encoder and application requirements first. Then verify which technologies the supplier owns, which parts come from third parties, and how system performance and lifecycle support are validated. See the China sourcing section and component sourcing service.
Need Help Sourcing Servo Motors?
If you have defined the joint load case, motion profile and motor-drive requirements, Yana can help structure supplier research, servo-system comparison and validation planning for robotics components in China.