Robotic Arm Joint Actuators and Gearboxes¶

Application Overview¶

Robotic arms, collaborative robots, research manipulators and compact automation systems require reliable joint-drive solutions for base, shoulder, elbow, wrist and rotary-tool axes. A robot arm joint actuator or robot arm gearbox should be selected from the complete mechanism requirement, not from output torque alone.

Each axis has a different payload, reach, center of gravity, inertia, motion profile, duty cycle, positioning target, brake requirement and installation envelope. The correct actuator selection depends on the relationship between torque, speed, backlash, stiffness, thermal behavior, controller capability and mechanical interface.

SigGear supports robotic arm projects with integrated robot joint actuators, planetary joint actuators, cycloidal joint modules and compact planetary gearboxes. Depending on the selected configuration, the solution may be supplied as a complete motor-reducer-encoder-driver module or 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 product selection, quotation and technical agreement require confirmation against the controlled drawing, selected ratio, duty cycle, mounting interface, motor configuration and ordered version.

Key Selection Factors for Robot Arm Joints¶

Requirement	Why it matters
Payload and reach	Determines gravity torque, inertia and the torque required at the base, shoulder and elbow axes.
Continuous torque	Must cover repeated motion, holding and process-load conditions within the required duty cycle.
Peak torque and peak duration	Important for acceleration, deceleration, collision recovery and short overload events.
Output speed and acceleration	Must match cycle time, path planning and production throughput targets.
Backlash and repeatability	Affect positioning accuracy, contouring quality, vibration and end-effector precision.
Radial, axial and overturning loads	Influence output bearing selection, housing stiffness and mounting-interface design.
Brake and holding mode	Critical for vertical axes, gravity-loaded arms and safe power-off behavior.
Encoder, driver and communication	Affect closed-loop control, software integration, wiring and diagnostic functions.
Thermal condition and duty cycle	Determine whether the selected actuator can work repeatedly without overheating.

Axis-by-Axis Review¶

Base Axis¶

The base axis often carries the full arm structure, payload and tooling inertia. Important review items include overturning moment, output-bearing support, acceleration profile, cable routing, backlash and mounting stiffness. A robot arm base joint may need a larger safety margin than a wrist or tool axis.

Shoulder Axis¶

The shoulder joint is usually one of the highest-load axes because it moves the upper arm and downstream payload. Continuous torque, peak torque, holding mode, brake requirement and thermal performance should be reviewed carefully. The center of gravity of the full arm link is important for calculation.

Elbow Axis¶

The elbow axis often needs a balance between torque, speed, compact axial length and smooth positioning. For collaborative robots and light industrial arms, an integrated actuator may reduce prototype assembly time, but the final selection must still confirm duty cycle, backlash and repeated temperature rise.

Wrist Axes¶

Wrist pitch, roll and yaw axes usually require compact size, low weight, smooth motion and good repeatability. Smaller integrated actuators or planetary gearbox solutions may be considered when the payload and external process forces are moderate.

Rotary Tool Axis¶

A tool-rotation axis may prioritize speed, positioning, cable routing, compact output interfaces and integration with end effectors. Required radial load, axial load, shaft geometry and expected life should be defined before selecting the gearbox or actuator.

Published SigGear Reference Platforms¶

The following published SigGear models can be used as starting points for robotic arm actuator and gearbox selection. Final selection depends on the axis position, complete operating cycle, size limit, load condition 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 axes, grippers, compact rotary tooling or customer-designed servo motor assemblies, SigGear can also evaluate 8–42 mm planetary gearbox options. These are useful when the customer needs a robot arm gearbox rather than a fully integrated actuator.

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 Robot Arm Gearbox¶

A robotic arm project can use either an integrated actuator or a separate gearbox-and-motor architecture.

An integrated robot joint actuator may be suitable when the project needs a compact module with matched motor, reducer, encoder and driver options. This can simplify prototype assembly and reduce early-stage integration risk.

A separate robot arm gearbox may be suitable when the engineering team already has a servo motor, BLDC motor, controller, brake, encoder or custom housing. In that case, the gearbox input shaft, mounting pattern, ratio, speed limit, thermal condition and output interface must be reviewed carefully.

Neither architecture is automatically better. The right choice depends on the axis load, packaging, control system, supply-chain strategy, prototype schedule and production quantity.

Planetary Gearbox or Cycloidal Joint Module¶

A planetary joint actuator or servo planetary gearbox may be considered when compact integration, output speed, motor matching flexibility and broad configuration options are important.

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

The decision should not be based on a general rule. Compare the full torque-speed cycle, payload inertia, external loads, backlash target, stiffness, thermal condition, size, weight, brake requirement and control architecture.

Backlash, Stiffness and Positioning Accuracy¶

Robot arm accuracy is not determined by the reducer alone. Backlash, structural stiffness, bearing arrangement, encoder position, controller tuning, arm-link rigidity and assembly tolerances all influence final positioning and repeatability.

When discussing a robotic arm gearbox or actuator, provide the required positioning accuracy and repeatability at the end effector, not only at the motor or reducer. This helps determine whether the selected gearbox, encoder and mechanical structure are suitable.

Brake, Safety and Holding Requirements¶

For vertical or gravity-loaded robot arm axes, specify the required holding condition and power-off behavior. A brake may be needed for safety or position retention, but it should not be assumed to be included unless it is confirmed in the selected configuration, drawing and quotation.

Important questions include:

Does the axis need to hold position when power is off?
Is the brake used for safety, parking or emergency stop support?
What payload and arm posture must be held?
Is backdrivability required or prohibited?
Is a mechanical stop, counterbalance or external brake also used?

Encoder, Driver and Communication Review¶

Robotic arm teams should confirm the control system early. Important questions include:

Is the actuator controlled by position, speed, torque or mixed control mode?
Is the driver integrated into the actuator or placed in the robot controller cabinet?
Is CAN, RS485, PWM or another interface required?
Is EtherCAT or another fieldbus handled by the customer controller?
What encoder resolution, absolute-position requirement and homing method are needed?
Are current limit, temperature feedback, fault reporting or brake control required?

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

Thermal and Duty-Cycle Validation¶

A robot arm actuator must be checked against the actual motion cycle. Useful information includes:

Rated and maximum speed
Acceleration and deceleration profile
Continuous torque during motion or holding
Peak torque and peak duration
Cycle time and rest time
Ambient temperature and cooling method
Mounting structure and heat-dissipation path
Expected daily operating hours

Peak torque is not a continuous working rating. A drive that can provide short overload torque may still be unsuitable if repeated motion causes 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
Brake integration after engineering review
Communication and control configuration
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 Robotic Arm Joint Selection Review¶

Please send one requirement set for each axis. Base, shoulder, elbow, wrist and tool axes should be reviewed separately.

Provide:

Robot type and target application
Axis position and motion direction
Payload, arm reach and center of gravity
Continuous torque
Peak torque and peak duration
Required output speed, acceleration and deceleration
Operating voltage and current limit
Maximum outer diameter, thickness and weight
Radial load, axial load and overturning moment
Backlash, positioning and repeatability targets
Brake and power-off holding 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 Robotic Arm Joint Selection Review¶

Send your robotic arm joint or gearbox requirements to SigGear for a preliminary model review. Early requirements can be approximate, but payload, reach, torque, speed, size, voltage and quantity are needed before a meaningful recommendation can be made.

Wanrong Wang
International Sales, SigGear
wangwanrong@siggear.com

Send Robotic Arm Requirements