Integrated actuators

Motor, transmission and feedback packaged into a joint that moves and supports the robot.

Inside a rotary actuator

SpryDrive 8318: inspect a real motor, planetary transmission, output bearing and encoder assembly.

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SpryDrive 8318

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7 motor turns = 1 output turn.

Source & model scope

Benjamin Bokser’s SpryDrive 8318 STEP assembly. Original part placements are preserved; the separate fasteners are hidden to keep the main assemblies clear. The section view clips the display to expose internals. This is one open actuator design, not the internal design of other products on this page. Movement follows the source’s 7:1 fixed-ring planetary arrangement. The input gear rotates seven times per output turn. Bearing rolling contact, motor electromagnetic forces, loads and efficiency are not simulated.

Original design · MIT licence · Conversion notes

Representative products

Component directory
Architecture, materials & specificationsArchitecture options, material requirements and integration constraints

Architecture options

Quasi-direct drive combines a high-torque motor with low reduction. Gearbox type and reduction ratio are separate choices.

ApproachMechanismAdvantagesTrade-offs
High-ratio gearedA faster motor drives a large speed reduction. For the same motor, its inertia felt at the joint grows with the square of the ratio.Reduces the motor torque needed for a given joint load.Reducer stiffness, friction and load limits shape output performance. Holding a load with power off may require a brake.
Quasi-direct driveA higher-torque motor uses a low reduction ratio.Can reduce resistance to externally imposed motion, supporting responsive contact control.Less torque multiplication requires more motor torque. Motor size, drive current and cooling are closely coupled. Impact durability depends on the complete joint.
Screw-driven linearA screw produces extension; a linkage turns it into joint rotation.Allows force-producing hardware to sit along the limb.Changing leverage changes joint torque and speed through the stroke. Screw supports, side-load guidance and lubrication add integration requirements.

Specifications & operating limits

Continuous output torque is tied to speed and cooling conditions; peak torque describes a limited duration with a recovery interval. Torque-to-mass comparisons depend on which components are included in the mass. Backlash is clearance on reversal; stiffness describes deflection under load. Backdrivability describes how easily external force moves the joint. Positioning accuracy and impact life depend on the assembled joint.

Materials & constraints

Copper, magnetic steel & magnets
A typical permanent-magnet motor combines current-carrying windings, a magnetic circuit and rotor magnets. Continuous output depends on getting heat out; the magnet, insulation and electronics each have their own temperature limits.
Hardened gears & bearing steels
Contact surfaces carry concentrated loads. Hardness resists wear, while toughness and fatigue strength help withstand repeated loading. Heat treatment, tooth geometry and lubrication affect wear and fatigue.
Load-bearing housings
The joint body holds the motor, gears and bearings in alignment while transferring loads into the limb. Aluminium offers low mass and useful heat conduction; steel offers greater stiffness for the same geometry, at greater mass. Ribs, wall thickness and bearing-seat geometry determine how much the finished housing flexes.
Thermal contact & mounting
Heat passes from the stator through its mounting interface and housing to the surroundings. Gaps and poorly conducting bonds restrict this path; bearings, lubricant and electronics have separate temperature limits.

Dependencies & engineering limits

Work cycle & heat
An actively held load can draw motor current even at zero speed. The resulting heat limits how long a joint can hold or repeat a movement. Continuous capability depends on the motion cycle, rest periods, heat path and drive-current limit.
Frameless motors
Manufacturing & assembly
Gear geometry, bearing fits and housing alignment determine how the assembled joint carries load. Assembly also requires feedback setup and checks through the motion range. Buying the motor and reducer therefore leaves precision assembly and verification work; integration transfers some of that work to the module supplier.
Bearings
Drive electronics & interfaces
Integrated drivers combine power transistors, gate drive and current sensing to save board space. Separate transistors allow different current and thermal requirements. Bus voltage, feedback interfaces and sustained current capability determine which motor and controller combinations work together.
Compute & control
Harness motion & service
Bending and twisting stress cables differently. Cable construction, bend radius and connector access constrain the route through the joint. Strain relief keeps that motion from pulling on terminations; its placement must still allow the cable to twist and bend through the full travel.
Structure & materials

Manufacturing & assembly

Guide

About this route

The route shows one process or architecture. Select a step to see its function and connections; related parts can be parallel inputs or alternatives.

Function

Inputs & dependencies
Outputs & connections
Related processes & parts
Sources

Manufacturing · Representative route. A sintered NdFeB, permanent-magnet motor route.

Related parts & processes 8

NdFeB alloy

Neodymium, iron and boron form the magnetic alloy in this sintered-magnet route. Grade selection trades magnetic performance against temperature requirements.

Heavy-rare-earth additions vary by grade.

Sources & technical scope

Illustrative images of generic materials and components.

Related references
Link to this detail

Production equipment

Market context

Unitree · quadruped production and sales

26,032Quadrupeds produced · 2025
23,037Quadrupeds sold · 2025

Annual production and recognised sales of quadruped robots.

Lens · DOBOT assembly and component order

10,000Rover X1 robots · assembly order

Complete-machine assembly order for Rover X1.

Rare-earth magnets

China’s share of global outputChina Rest of world
China · global sintered-magnet output94%
China · global magnet rare-earth refining91%

Global supply across industries. Refining and finished magnets are separate dependencies for permanent-magnet motors.

Direct Drive

Direct Drive Tech shipped 12,878 embodied joint modules in H1 2026, up from 3,898 a year earlier. Average selling price fell from RMB763 to RMB257 as its product mix broadened across price points.

Unitree

Unitree assembles robots and core modules internally. It buys custom mechanical parts and outsources most PCB assembly, injection moulding and some machining.

MEVIUS2 · twelve purchased joint motors

MEVIUS2 uses twelve RobStride03 motors. Its open parts list combines purchased actuator modules with separately fabricated links and housings.

maxon

ANYbotics assigned development and production of ANYmal actuators to maxon. Each robot uses twelve drive systems; the agreement moved the actuator programme from small-series development toward industrial production.

Explore documented supply relationships →