Humanoid Robot Joint Actuator Selection Guide¶

Selecting a humanoid robot joint actuator requires matching torque, speed, gearbox architecture, installation size, weight, duty cycle and control requirements for each axis. Shoulder, elbow, wrist, hip, knee, ankle, neck and waist joints should not be sized from peak torque alone.

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Application Overview¶

Humanoid and bipedal robots require compact joint actuators for the shoulder, elbow, wrist, hip, knee, ankle, neck and waist axes. Each joint has a different torque-speed cycle, external-load condition, installation envelope, thermal limit and control requirement. A humanoid robot joint actuator should therefore be selected from the complete operating profile, not from peak torque alone.

For a bipedal robot joint actuator, each hip, knee, ankle, shoulder, elbow and wrist axis should be evaluated separately because its torque-speed cycle, packaging, external loads and duty cycle can be different.

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

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

When a Standard Robot Actuator Gearbox Does Not Fit¶

A humanoid or bipedal robot project may need a different torque-speed balance, motor, reduction ratio, diameter, axial thickness, output interface, encoder, driver or communication arrangement than an existing catalog actuator.

In that case, the starting point should be the joint requirement rather than a forced model selection. Send the joint position, mechanism, available space, target motion and the motor or controller information already defined.

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How to Select a Humanoid Robot Joint Actuator¶

A practical early-stage selection process should cover the following steps:

Define the joint position and motion cycle — Separate shoulder, elbow, wrist, hip, knee and ankle requirements instead of applying one actuator specification to every axis.
Calculate continuous and peak torque — Include gravity, acceleration, external forces, mechanism losses and the duration and frequency of peak events.
Match output speed and power — Check torque and speed at the same operating point and confirm the available voltage and controller current limits.
Set the installation envelope — Define maximum diameter, axial thickness, length, weight, cable space, bearing arrangement and output interface.
Choose the transmission architecture — Compare planetary and cycloidal options, or an integrated actuator versus a separate motor and gearbox.
Confirm control and thermal conditions — Review encoder, driver, communication, duty cycle, cooling, brake and power-off behavior.
Validate with a prototype — Test the actuator in a representative mechanism with realistic loads, motion cycles and temperature monitoring.

For torque formulas, sizing steps and a complete engineering checklist, use the Robot Joint Actuator Selection Guide.

What a Humanoid Joint Actuator Must Define¶

A humanoid joint is not defined only by rated torque. The following parameters should be reviewed together:

Requirement	Why it matters
Continuous torque	Determines whether the joint can sustain walking, lifting, balancing or holding conditions without overheating.
Peak torque and peak duration	Important for acceleration, recovery motion, impact events and short overload conditions.
Output speed	Must match the robot motion profile and motor operating range.
Outer diameter and axial thickness	Controls whether the actuator fits inside the limb, torso or joint shell.
Weight	Affects leg swing inertia, arm payload, power consumption and whole-body balance.
Backlash and positioning requirement	Influences stability, repeatability, force control and motion smoothness.
Radial, axial and overturning loads	Affect the bearing, housing and output-interface design.
Duty cycle and cooling	Determine whether torque values are usable continuously or only for short periods.
Encoder, driver and communication interface	Affect closed-loop control, wiring, protocol integration and software development.

Joint Positions and Typical Review Focus¶

Shoulder Joint¶

The shoulder may include pitch, roll and yaw axes. It often requires compact packaging, sufficient peak torque for arm acceleration and careful cable routing through the upper body. External loads from the arm, gripper and carried object should be considered.

Elbow Joint¶

The elbow usually needs a balance between torque, speed and compact axial length. For prototype humanoid arms, an integrated actuator can reduce assembly work, but the final selection should still confirm continuous holding torque, backlash and thermal conditions.

Wrist Joint¶

The wrist is sensitive to size and weight. Lower inertia and compact output interfaces are usually important. Small planetary gearboxes or compact joint actuators may be considered when the required torque is lower than the shoulder or elbow.

Hip Joint¶

The hip is one of the highest-load areas in a humanoid robot. It may require higher continuous torque, high peak torque and strong structural support. Overturning moment, radial load, shock load and housing stiffness are especially important.

Knee Joint¶

The knee joint is strongly affected by walking, squatting, standing-up and impact recovery cycles. Continuous torque, peak duration, braking strategy, thermal behavior and mechanical safety margin should be reviewed carefully.

Ankle Joint¶

The ankle often combines torque, shock load and packaging difficulty. It can be sensitive to backlash, compliance, sealing, cable routing and impact load. Prototype testing is usually important before locking the actuator model.

Published SigGear Reference Platforms¶

The following published SigGear models can be considered as starting points for humanoid robot joint evaluation. Final selection depends on the exact joint position, torque-speed cycle, duty cycle, external loads, size limits 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 smaller auxiliary joints, sensor mechanisms, hands, compact wrists or lightweight adjustment axes, SigGear can also evaluate 8–42 mm planetary gearbox options when the customer already has a motor or needs a customized motor-gearbox combination.

Public Engineering Resources¶

For engineers moving from model screening into mechanical evaluation, SigGear currently publishes engineering resources for selected reference platforms:

SG-6010C¶

technical datasheet
mechanical-interface reference
simplified STEP model

View SG-6010C Engineering Resources

CPM-80-25¶

technical datasheet
mechanical-interface reference
simplified STEP models
measured performance data

View CPM-80-25 Engineering Resources Open the Engineering Center

Integrated Actuator or Separate Gearbox and Motor¶

A humanoid project may use an integrated actuator or a separate gearbox-and-motor architecture.

An integrated robot joint actuator may be suitable when the engineering team wants a more complete module with a matched motor, reducer, encoder and driver option. This can reduce early prototype integration work and speed up testing.

A separate gearbox and motor solution may be suitable when the robot team already has its own motor, controller, encoder, housing or thermal design. In this case, the gearbox interface, input speed, motor shaft, mounting pattern and output shaft must be confirmed carefully.

SigGear can support both approaches depending on the model, quantity, customization scope and engineering feasibility.

Motor + Gearbox Integration Engineering Custom Robot Joint Actuator Development

Planetary or Cycloidal Drive for Humanoid Robots¶

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

Engineers evaluating an existing planetary joint-drive platform can also review SigGear's published robot joint actuator models and their released specifications.

Planetary Robot Joint Actuators

A cycloidal joint module may be considered when the application requires compact high-torque transmission and the selected model's speed, backlash, installation structure and duty cycle match the joint requirement.

Neither transmission type should be selected from a general rule alone. Compare the complete torque-speed cycle, external loads, backlash target, thermal condition, size limit, weight target, control architecture and production plan.

Control, Encoder and Communication Review¶

Humanoid robot teams should confirm the control architecture early. Important questions include:

Is the joint controlled by position, speed, torque or mixed control mode?
Is the driver integrated into the actuator or placed on a separate robot controller board?
Is CAN, RS485, PWM or another interface required?
What encoder resolution and position feedback accuracy are needed?
Is the control loop closed at the actuator, at the main robot controller or both?
Are there requirements for current limit, temperature monitoring, fault reporting or brake control?

Communication and control functions vary by selected product and electronics configuration. Do not assume CAN, RS485, EtherCAT, PID, torque control or a specific protocol without confirming the driver and firmware version.

Torque, Speed and Thermal Selection¶

For each joint, provide the full motion cycle instead of only the maximum torque value. Useful information includes:

Continuous torque during holding or walking
Peak torque and peak duration
Target output speed and acceleration
Operating voltage and current limit
Motion time, rest time and duty cycle
Ambient temperature and cooling method
Mounting structure and heat dissipation path
Expected test duration and service-life target

Peak torque is not a continuous working rating. A joint that can provide short peak torque may still be unsuitable if the repeated duty cycle causes excessive temperature rise.

Open the torque calculation and actuator sizing guide

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
Customer branding and labeling
Prototype support before production planning

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

From Prototype to Design-In¶

After a preliminary actuator or gearbox configuration is selected, the project can move through sample evaluation, application testing, interface refinement, design confirmation and pilot preparation.

Prototype → Design-In → Production

Information Needed for a Humanoid Joint Selection Review¶

Please send one requirement set for each joint position. For example, shoulder, elbow, wrist, hip, knee and ankle should be reviewed separately.

Provide:

Robot type and target application
Joint position and axis definition
Continuous torque
Peak torque and peak duration
Required output speed
Operating voltage and current limit
Maximum outer diameter, thickness and weight
Radial load, axial load and overturning moment
Backlash and positioning requirement
Encoder, driver and communication requirements
Duty cycle, ambient temperature and cooling method
Prototype quantity and estimated annual quantity
Preferred architecture: integrated actuator or separate gearbox and motor

Request a Joint Selection Review¶

Send your humanoid robot joint requirements to SigGear for a preliminary model review. Early requirements can be rough, but torque, speed, size, voltage and quantity are needed before a meaningful recommendation can be made.

Wanrong Wang
International Sales, SigGear
wangwanrong@siggear.com

Request CAD, Sample and Quote Send Humanoid Joint Requirements