Quadruped Robot Joint Gearboxes and Actuators¶

Application Overview¶

Quadruped robots require compact and durable joint-drive systems for hip, knee, ankle and auxiliary leg axes. Walking, trotting, turning, stair climbing, slope operation, jumping, landing and recovery motions create different torque-speed and impact-load conditions. A quadruped robot actuator or leg joint gearbox should therefore be selected from the complete gait profile, not from a single peak-torque value.

SigGear supports quadruped robot development with integrated robot joint actuators, planetary joint actuators, cycloidal joint modules and compact planetary gearbox solutions. Depending on the selected configuration, the solution may combine a motor, reducer, encoder and driver, or it may be supplied as a reducer or gearbox for customer-side motor and controller integration.

This page is intended for early-stage supplier comparison, model shortlisting and engineering communication. Final actuator selection, quotation and technical agreement require confirmation against the controlled drawing, selected ratio, duty cycle, mounting interface, impact condition, motor configuration and ordered version.

Key Selection Factors for Quadruped Robot Joints¶

Requirement	Why it matters
Robot mass and payload	Determines standing load, walking load and impact energy during landing or recovery.
Joint position	Hip, knee and ankle joints have different torque, speed, impact and packaging requirements.
Continuous torque	Must cover standing, walking and repeated gait cycles without excessive temperature rise.
Peak torque and peak duration	Important for acceleration, jumping, impact recovery and short overload events.
Output speed and acceleration	Must match gait frequency, stride length, foot trajectory and recovery motion.
Backlash and mechanical response	Affect foot placement, balance, compliance, motion smoothness and control stability.
Radial, axial and overturning loads	Influence output bearing, housing stiffness and leg-link structure.
Shock and impact loads	Critical for landing, obstacle crossing, sudden stops and repeated gait impact.
Encoder, driver and communication	Affect closed-loop control, wiring, software integration and diagnostic functions.
Thermal condition and duty cycle	Determine whether torque values are usable repeatedly or only for short periods.

Joint-by-Joint Review¶

Hip Joint¶

The hip joint usually experiences high structural load because it connects the leg to the robot body and supports body mass, payload and dynamic gait forces. Important review items include continuous torque during standing, peak torque during acceleration, overturning moment, radial load, axial load, mounting stiffness and cable routing.

Knee Joint¶

The knee joint is strongly affected by walking, trotting, squatting, jumping and recovery cycles. It may require high peak torque and repeated acceleration while remaining compact and lightweight. Thermal behavior, duty cycle, backlash and impact resistance should be reviewed carefully.

Ankle Joint¶

The ankle joint is often sensitive to impact load, backlash, mechanical compliance and packaging. Foot contact, slope operation, landing and uneven-ground walking can create repeated shock loads. The output bearing structure, sealing, cable route and mechanical stops should be discussed during prototype review.

Auxiliary Leg or Steering Axis¶

Some quadruped platforms include auxiliary rotary axes, steering structures, sensor-adjustment mechanisms or compact leg-link mechanisms. Smaller integrated actuators or planetary gearboxes may be suitable when torque and impact loads are lower than the main hip or knee joints.

Gait Profile and Torque-Speed Cycle¶

For quadruped actuator selection, the complete gait profile is more useful than a single torque number. Provide operating cases such as:

Standing and holding posture
Walking on flat ground
Trotting or fast walking
Turning and lateral motion
Starting and stopping
Slope climbing and descending
Obstacle crossing
Jumping, landing or recovery motion
Maximum payload condition

For each case, define continuous torque, peak torque, peak duration, output speed, acceleration, duty cycle and expected test time. Peak torque should not be treated as a continuous working rating.

Impact Load and Structural Review¶

Quadruped robot joints can experience repeated impact and shock. These loads are different from output torque and should be evaluated separately.

Important information includes:

Robot mass and payload
Leg length and joint layout
Foot contact condition
Maximum landing or recovery event
Ground surface and obstacle condition
Radial load, axial load and overturning moment at the joint
Mechanical stop or compliance design
Whether external bearings support the joint load

A gearbox or actuator that meets torque and speed requirements may still be unsuitable if the bearing, housing or output interface cannot support the real impact condition.

Published SigGear Reference Platforms¶

The following published SigGear models can be used as starting points for quadruped robot actuator and leg joint gearbox evaluation. Final selection depends on the joint position, robot mass, gait cycle, impact condition, size limit and control architecture.

Model	Transmission	Rated torque	Peak torque	Rated output speed	Configuration note
SG-6010C	Planetary	6 Nm	18 Nm	310 rpm	Driver options depend on selected configuration.
SG-6010D	Planetary	16 Nm	50 Nm	100 rpm	Available with or without integrated driver.
SG-8021	Planetary	10 Nm	30 Nm	160 rpm	Driver options depend on selected configuration.
CPM-100-25	Cycloidal pinwheel	25 Nm	75 Nm	60 rpm	Available with or without integrated driver.
CPM-80-25	Cycloidal pinwheel	10 Nm	50 Nm	120 rpm	Available with or without integrated driver.
CPM-78-39	Cycloidal pinwheel	20 Nm	52 Nm	48 rpm	Standard catalog configuration uses Hall sensors and no integrated driver.

For small auxiliary mechanisms, sensor modules, compact ankle mechanisms or customer-designed motor assemblies, SigGear can also evaluate 8–42 mm planetary gearbox options when the application requires a separate reducer or compact gearbox.

Public Engineering Resources¶

Selected public engineering resources are available for preliminary design evaluation:

SG-6010C: datasheet, mechanical-interface reference and simplified STEP model
CPM-80-25: datasheet, mechanical-interface reference, simplified STEP models and measured performance data

Open the Engineering Center

Integrated Actuator or Separate Gearbox and Motor¶

A quadruped robot project can use an integrated actuator or a separate gearbox-and-motor architecture.

An integrated robot joint actuator may be suitable when the team wants a compact module with matched motor, reducer, encoder and driver options. This can reduce prototype assembly work and speed up early gait testing.

A separate leg joint gearbox may be suitable when the robot team already has its own motor, controller, encoder, brake, housing, external bearing or leg-link structure. In that case, the input shaft, mounting interface, output shaft, ratio, speed limit, bearing arrangement and heat-dissipation path must be confirmed carefully.

The best architecture depends on robot mass, leg layout, required torque-speed cycle, impact condition, serviceability, prototype schedule and production quantity.

Planetary or Cycloidal Drive for Quadruped Robots¶

A planetary joint actuator may be considered when the project prioritizes compact integration, output speed, motor matching flexibility and broad configuration options.

A cycloidal joint module may be considered when the selected model's torque, speed, backlash, installation structure and duty-cycle capability match the leg-joint requirement.

Neither transmission type should be selected from a general rule alone. Compare the full torque-speed cycle, impact load, backlash target, stiffness, thermal condition, size, weight, control architecture and prototype validation plan.

Control, Encoder and Communication Review¶

Quadruped robots often require responsive closed-loop control. Before selecting a joint actuator, confirm:

Is the joint controlled by position, speed, torque or mixed control mode?
Is the driver integrated into the actuator or placed on a robot controller board?
Is CAN, RS485, PWM, EtherCAT or another interface required?
What encoder resolution and absolute-position behavior are needed?
Is current limiting, temperature feedback or fault reporting required?
Does the robot need power-off holding, brake control or controlled backdrivability?

Communication and control functions vary by selected product and electronics configuration. Do not assume CAN, RS485, EtherCAT, PID, torque control or a specific protocol until the driver and firmware version are confirmed.

Thermal and Duty-Cycle Validation¶

Quadruped joints can produce repeated heat because gait cycles often involve frequent acceleration, deceleration, impact recovery and holding. Provide the real operating cycle instead of only maximum torque and speed.

Useful information includes:

Continuous torque during standing or walking
Peak torque and peak duration
Output speed and acceleration
Gait cycle and duty cycle
Operating time and rest time
Ambient temperature and cooling method
Mounting structure and heat-dissipation path
Expected daily operating hours and service-life target

Peak torque is not a continuous working rating. A joint that can provide short overload torque may still be unsuitable if repeated gait cycles cause excessive temperature rise.

Robot Joint Actuators Robot Joint Actuator and Gearbox Selection Guide Request CAD, Sample and Quote

Engineering Development Paths¶

Robot Joint Actuator and Gearbox Selection Guide Custom Robot Joint Actuator Development Motor + Gearbox Integration Engineering Open the Engineering Center Prototype → Design-In → Production

Prototype and Customization Support¶

Depending on the selected model and project scope, SigGear can evaluate:

Motor, reducer, encoder and driver integration
Reduction-ratio and output-interface customization
Mounting and housing customization
Cable and connector customization
Communication and control configuration
Brake or holding requirements after engineering review
Prototype support before production planning

Customization availability depends on technical feasibility, prototype quantity, expected annual volume and the level of engineering change required.

Information Needed for a Quadruped Joint Selection Review¶

Please send one requirement set for each joint position. Hip, knee, ankle and auxiliary axes should be reviewed separately.

Provide:

Robot type and target application
Robot mass and maximum payload
Joint position and axis definition
Leg length and mechanical layout
Continuous torque
Peak torque and peak duration
Required output speed and acceleration
Gait profile and duty cycle
Operating voltage and current limit
Maximum outer diameter, thickness and weight
Radial load, axial load and overturning moment
Shock, landing or obstacle-crossing condition
Backlash and positioning requirement
Encoder, driver and communication requirements
Ambient temperature and cooling method
Prototype quantity and estimated annual quantity
Preferred architecture: integrated actuator or separate gearbox and motor

Request a Quadruped Joint Selection Review¶

Send your quadruped robot joint requirements to SigGear for a preliminary model review. Early requirements can be approximate, but robot mass, joint position, torque, speed, gait cycle, impact condition, voltage and quantity are needed before a meaningful recommendation can be made.

Wanrong Wang
International Sales, SigGear
wangwanrong@siggear.com

Send Quadruped Joint Requirements