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Why Permanent Magnets Are the Core of Modern Robot Motion Systems
Between 2024 and 2026, the global robotics industry entered a historic inflection point. Tesla Optimus, Figure 02, Agility Digit, the new Boston Dynamics Atlas, Unitree H1, AgiBot A2, UBTech Walker S, Fourier GR-1, XPeng Iron, Xiaomi CyberOne, and a wave of other humanoid robots moved from lab demos to factory trials. At the same time, established markets for industrial robot arms, mobile AGV/AMR fleets, surgical robots, exoskeletons, drones, and cleaning robots continued to grow at double-digit rates. Permanent magnets — especially sintered neodymium-iron-boron (NdFeB) — are one of the core enabling materials of this industrial explosion.
Why? Because every critical node of a robot motion system — servo motors, harmonic reducers, magnetic encoders, hub motors, voice-coil actuators, magnetic grippers — is built around permanent magnets. A rough estimate: each humanoid robot uses 28 to 50 servo joint motors, 20 to 40 magnetic encoder rings, plus multiple sensor and gripper magnets, corresponding to roughly 2 to 5 kg of sintered NdFeB per unit, with a total magnet-system value of USD 200 to 500 per robot. A 2025 Goldman Sachs report projects that by 2035, global humanoid robot annual shipments will exceed one million units, corresponding to an additional 2,000 to 5,000 tons of high-end sintered NdFeB demand every year — a full ten-thousand-ton-class new material industry built from a near-zero base.
This article systematically explains where magnets are used in each robot subsystem, covering joint motors, magnetic encoders, end effectors, wheel drives, linear motors, and magnetic couplings. We then drill into three mainstream robot topologies — humanoid robots, mobile robots (robotic vehicles), and robot arms. Finally, we look at the next 5 to 10 years of robotics industry development.
Of all permanent magnet families, only three see high-volume use in robotics: sintered NdFeB, samarium cobalt (SmCo), and bonded NdFeB. Understanding their performance boundaries is the first step in robot magnet selection.
Sintered NdFeB is the workhorse. Grades span N35 to N52 in the standard temperature range, N42M/N40M/N38M in the medium-temperature range (100°C), N42SH/N40SH/N38SH in the high-temperature range (150°C), N40UH/N38UH/N35UH in the ultra-high-temperature range (180°C), N38EH/N35EH in the extreme range (200°C), and N35AH in the aerospace range (220°C). Mainstream robot choices are N42SH and N40UH — the former for most industrial use cases, the latter for robot joints where thermal stability is critical. Sintered NdFeB delivers the highest energy product (BHmax above 50 MGOe), which is exactly the high-torque-in-small-volume capability that robots demand.
Samarium cobalt (SmCo) is reserved for extreme environments. SmCo₁:₅ operates continuously from 250°C to 300°C; Sm₂Co₁₇ from 300°C to 350°C. SmCo is also corrosion-resistant and radiation-tolerant, making it the first choice for aerospace, nuclear, and downhole robots. The downsides are 20–30% lower energy product than NdFeB and 2–4× higher cost.
Bonded NdFeB is used for complex shapes. Compression-molded or injection-molded bonded magnets can realize thin walls and irregular geometries that are difficult with sintered material. The trade-off is energy product at 50–70% of sintered level. Bonded NdFeB is mainly used in encoder rings, sensor magnets, and low-cost hub motors.
Ferrite is almost never used in robot main drives — its torque density is too low, except in consumer-grade low-cost service robots. AlNiCo is essentially absent — its coercivity is too low, making it vulnerable to demagnetization under vibration and shock.
Servo joint motors are the largest and highest-value magnet application in any robot. Every humanoid has 28 to 50 active joints, with at least one brushless servo motor per joint. Each six-axis industrial arm has one motor per axis. Each AGV/AMR drive wheel has one hub motor.
The core magnetic circuit of a joint motor is the rotor magnet assembly — sintered NdFeB arc segments (tile-shaped) arranged in alternating N/S polarity, bonded or bolted to a steel back-yoke, forming a radial multi-pole or Halbach array. Typical dimensions: outer diameter 18–100 mm, pole count 4–28, axial length 10–80 mm.
Halbach arrays are the key technology for high-end joint motors. A conventional radial-magnetized rotor has roughly half the flux exit through the air gap to the stator and the other half loop back through the rotor back-iron, which limits air-gap flux density. A Halbach array uses a special magnetization-direction layout (each magnet block is rotated by 360°/pole-pairs) to concentrate the flux almost entirely on the air-gap side and nearly eliminate back-iron flux. The result: air-gap flux density increases by 25–40% with the same amount of magnet material, or magnet usage decreases by 30–40% at the same flux density. This is revolutionary for the small-volume-high-torque demand of robot joints.
Typical magnet solutions for robot joint motors:
· Knee, shoulder, hip joints (large joints): OD 50–100 mm, axial length 30–60 mm, 14–24 poles, N42SH or N40UH, Halbach array.
· Elbow, wrist joints (medium joints): OD 30–60 mm, axial length 20–40 mm, 8–16 poles, N40SH, Halbach or radial multi-pole.
· Finger joints (small joints, most challenging): OD 15–30 mm, axial length 10–25 mm, 2–8 poles, N40UH or N42SH, Halbach array, 12–17 motors per hand, requiring 12–17 Halbach rotors per hand.
Key quality parameters: pole-arc coefficient, magnetic flux uniformity (±3%), dynamic balance grade (G2.5/G1.0), coaxiality (0.02–0.05 mm TIR), bonding temperature resistance (peak 150°C), impact resistance (above 5G). Multiple leading humanoid robot manufacturers have already gone into volume production with Halbach joint rotors covering OD 18–100 mm.
Every joint motor and every drive wheel needs position feedback. Magnetic encoders have largely replaced optical encoders in robots because of small size, contamination tolerance, vibration resistance, and low cost.
A magnetic encoder works as follows: a magnet ring (radially magnetized, one or multiple pole pairs) is fixed on the rotating shaft. Hall sensors or TMR (tunneling magnetoresistance) sensors above the ring detect field changes and output sine/cosine signals or ABZ pulses, with resolutions from 12-bit to 24-bit (4,096 to 16,777,216 pulses per revolution).
Key parameters for encoder rings:
· Outer diameter: 8–50 mm
· Inner diameter: 3–30 mm
· Thickness: 2–8 mm
· Pole count: 1–64 (more poles = higher resolution)
· Material: bonded NdFeB (most) or sintered NdFeB (high-end)
· Surface coating: Ni-Cu-Ni or epoxy
· Magnetic uniformity: ±2%–5%
Monthly production of encoder magnet rings can reach over 100,000 pieces, covering the full OD 8–50 mm range.
Beyond encoders, robots also use Hall current sensors (for phase-current sensing in power modules), magnetic switches (limit and zero-position detection), magnetoresistive sensors (joint angle and torque sensing). Each of these requires precision magnet support.
The "hand" of a robot — the end effector — falls into three categories by working principle: mechanical gripper, vacuum gripper, and magnetic gripper. Magnetic grippers are used for handling ferromagnetic workpieces (steel, cast iron, ferrous parts), with advantages of simple structure, no air supply, fast response, and long life. Typical applications: machine tool loading, stamping part pick-and-place, iron-chip cleaning, steel-coil handling.
The core of a magnetic gripper is a NdFeB block or cylinder magnet (N35–N42) flux-concentrated by a steel pole piece. A single gripper delivers 50–5,000 N of holding force, with magnet sizes from 10×10×5 mm up to 100×100×30 mm. Quick-change mechanisms often use permanent-magnet retention with spring release designs, with magnet sizes 20–50 mm and holding force 100–500 N.
Mobile robots (AGVs, AMRs, service robots, cleaning robots, delivery robots) use hub motors or geared drive motors as their core drive units.
Hub motors integrate the motor inside the wheel rim, eliminating the gearbox and drive shaft, saving space. They require high torque density and high efficiency. Typical specifications: OD 100–300 mm, power 100 W–3 kW, speed 100–1,000 RPM (direct drive) or 3,000–6,000 RPM (geared), N42SH magnets, Halbach or radial multi-pole magnetic circuit.
AGV/AMR drive motors typically use geared servo motors with encoders, with magnet solutions similar to industrial servos. Multiple AGV/AMR manufacturers have already gone into volume production with high-performance hub motors, OD 100–250 mm, with monthly supply exceeding 5,000 pieces.
Linear motors are the darlings of high-end robot applications — semiconductor lithography (ASML), wafer inspection, panel inspection, lithium-battery electrode winding, and laser cutting all require nm-to-μm precision and 1–10 g acceleration in linear motion.
Linear motors come in moving-magnet and moving-coil variants. The magnet track is composed of a Halbach array or N/S alternating-pole arrangement of sintered NdFeB blocks. Each block measures 10–30 mm wide × 5–15 mm high × 100–500 mm long, with pole pitch 10–30 mm. Multiple semiconductor equipment manufacturers have adopted high-performance magnet track assemblies.
Voice-coil motors (VCMs) are a special form of linear motor, simpler in structure and faster in response (ms level), used in lens focusing, vibration modules, dispensing valves, and laser galvos. Magnet ID 5–50 mm, axial length 5–30 mm.
Humanoid robots are the hottest robot segment and the most magnet-intensive. Below we go through every body part.
Full-body motor distribution (typical 28–50 active joints):
· Neck: 2–3 motors (pitch, yaw, roll)
· Shoulders: 3–6 per side (flexion, abduction, rotation)
· Elbows: 1–2 per side
· Wrists: 2–4 per side
· Fingers: 12–17 per hand (thumb 4, others 3 each)
· Waist: 2–6
· Hips: 3–6 per side
· Knees: 1–2 per side
· Ankles: 2–3 per side
· Toes/sole: 0–5 (optional)
Representative models and magnet consumption:
· Tesla Optimus: 28–40 actuators, Halbach joint motors, magnet-system value USD 200–400 per unit.
· Figure 02: 35+ motors, emphasis on hand dexterity, 17 DOF per hand.
· Unitree H1: 19 main joints; G1 expands to 23+, low-cost focus.
· Agility Digit: 16 leg joints, logistics emphasis.
· Boston Dynamics new Atlas: fully electric, 28+ joints.
· 1X Neo: home humanoid, 21 DOF.
· Fourier GR-1: 44 actuators, 17 DOF per hand.
· UBTech Walker S: 41 servo joints.
· XPeng Iron: human-like, fine manipulation focus.
· Xiaomi CyberOne: 21 DOF full body.
· AgiBot A2: 40+ actuators.
· Accelerating Evolution T1: 16 DOF, competition/humanoid hybrid.
Finger joints are the most challenging battleground for magnet vendors. Each hand has 12–17 motors, requiring 12–17 Halbach rotors with OD 15–25 mm, axial length 10–20 mm, requiring extreme torque density (25–40 kN·m/m³), minimal magnetic eccentricity, and strict dynamic balance (G1.0).
Knee/hip large joints are another technical high ground. Halbach arrays OD 80–100 mm, axial 40–60 mm, must deliver 30–80 N·m continuous torque and 150+ N·m instantaneous shock, using N42SH/N40UH materials, with back-yoke and shaft sleeve integrated precision-machined.
Waist-to-hip connection torsional joints require large-diameter Halbach arrays (OD 60–100 mm, axial 30–50 mm), bearing tri-axial torque, demanding high magnetic-circuit symmetry and mechanical strength.
Ankle active compliance control requires high-response servo motors, magnet OD 30–50 mm, 4–10 poles.
Wrist rotation motors need 6+ poles with fine pole pitch, magnet OD 25–40 mm, commonly Halbach.
AGVs (Automated Guided Vehicles) and AMRs (Autonomous Mobile Robots) are the two mainstream forms of industrial logistics. AGVs follow magnetic tape or magnetic nails; AMRs use SLAM-based autonomous navigation. Both require:
· Drive motors: differential or omnidirectional drive, one motor per wheel, OD 100–200 mm, 100–500 W.
· Steering motors (some models): OD 60–120 mm, 50–200 W.
· Lifting motors: OD 80–150 mm, 500–2,000 W.
· Encoders: magnetic rings OD 20–40 mm.
· Magnetic navigation (AGV only): magnetic-tape sensing magnets.
Warehouse robot leaders: Amazon Robotics (Kiva), Geek+, Quicktron, Hikvision Robotics.
Delivery robots (hotels, restaurants, hospitals, food delivery): Pudu, Keenon, UBTech, Segway. Magnet demand is dominated by hub motors, OD 100–200 mm.
Service robots (reception, guidance, inspection): Yunji, OrionStar, UBTech Cruzr. Magnets are mainly small-size servos.
Cleaning robots: vacuum (Roborock, Ecovacs, iRobot), floor scrubbers, commercial cleaners. Hub motors are extremely small (OD 30–80 mm) but in massive monthly volume.
Agricultural robots: driverless tractors, harvesting robots, plant-protection drones. Magnets are hub motors and propeller motors.
Industrial robot arms fall into four main configurations: 6-axis articulated, SCARA, Delta (parallel), and collaborative robots (cobots).
6-axis articulated (most common): KUKA, ABB, FANUC, Yaskawa, Kawasaki, Nachi, Stäubli, Siasun, Estun, Leaderdrive, STEP. One servo motor per axis (some have redundancy with two). Main axis motor power 1–7.5 kW, small axis 50–500 W. Magnet solutions match industrial servos: radial multi-pole or Halbach array, N40SH/N42SH, OD 60–150 mm.
SCARA: horizontal articulated, 4 axes, used for assembly, dispensing, screw locking. Main axis motor OD 40–80 mm.
Delta (parallel): 3 or 4 axes, very high end-effector speed (>10 m/s pick-and-place), main axis motor 200 W–1 kW, with internal stator, magnet OD 60–100 mm.
Cobots: Universal Robots, Techman, JAKA, Han's, Dobot, Aubo. Emphasis on safety, collaboration, low-speed high-torque, with magnet solutions favoring small-size Halbach.
Harmonic reducers are the core transmission unit in robot arms; the output end requires high-precision magnetic encoders, so harmonic reducer manufacturers (Leaderdrive, Laifu, Suzhou Lvdi, Han's Precision) are all potential customers for encoder magnet rings.
Medical robots:
· Surgical robots: da Vinci (4 arms + camera, multiple motors per arm), Mako orthopedic, ROSA neurosurgery, CorPath cardiovascular. Magnets are small-size high-precision, high cleanliness required.
· Rehabilitation robots: Lokomat, Armeo, exoskeleton joint motors.
· Prosthetics: intelligent prosthetic hands/legs, requiring extreme torque density joint motors.
· Capsule endoscopes: micro magnetic positioning.
Underwater robots (ROV/AUV):
· Thruster motors: 500 W–10 kW, deep-sea pressure-resistant (1,000–11,000 m), magnets use corrosion-resistant SmCo or epoxy-encapsulated NdFeB.
· Manipulator arms: 6-axis small-size servos.
Aerial robots (drones):
· Multirotor: FOC (field-oriented control) motors, high KV (800–2,500), 14–28 poles, small magnets (OD 20–50 mm), massive monthly volume.
· Fixed-wing/VTOL: higher-power motors.
· Cargo drones: 50–500 kW high-power motors.
Specialty robots:
· Rescue robots: nuclear incidents, fire, mine disasters, high protection grade.
· Military robots: quadruped, tracked, fixed-wing.
· Space robots: NASA Robonaut, Canadian Dextre, using SmCo for radiation resistance.
Torque density: torque output per unit weight/volume. Robot joints require >50 N·m/kg (high-end); Halbach magnetization is the inevitable path.
Size constraints: limited robot volume, requiring magnets to deliver maximum flux within 18–100 mm OD. Thin-wall magnet rings, Halbach arrays, and multi-pole designs are the primary solutions.
Temperature management: the difference between continuous and peak torque causes magnet temperature to swing between 80–150°C. Selecting N40UH instead of N42 reduces operating temperature by 20°C and increases life by 50%.
Cogging torque and torque ripple: affect motion smoothness. Controlled through skew, Halbach arrays, fractional-slot windings, and magnetic eccentricity compensation.
Reliability and lifetime: industrial robots require MTBF > 50,000 h (≈6 years continuous), humanoids 5–10 years. Magnet selection, surface treatment (Ni-Cu-Ni or epoxy), bonding process (temperature resistance >150°C), and mechanical fixing (bolt/interference) together determine reliability.
Vibration and shock resistance: mobile robots, robot arms, drones all experience >5G vibration. Bonding plus mechanical fixing (slot, end ring, bolt) is the mainstream approach.
1. Humanoid mass production will ignite magnet demand
Goldman Sachs' 2025 report projects global humanoid robot annual shipments of 1+ million by 2035, with optimistic scenario of 3 million. Tesla targets 1 million Optimus per year by 2030. If achieved, the global humanoid market will add 30,000–50,000 tons of sintered NdFeB demand annually — 10–15% of current global high-end sintered NdFeB production. Magnet capacity, rare-earth supply chain, and Halbach magnetic-circuit design capability will become choke points of the robotics industry chain.
2. New motor technologies continue to evolve
· Axial-flux motors (YASA, Magnax, Phi-Power): axial flux, flatter structure, higher torque density, gradually entering humanoid main drives.
· Halbach arrays: becoming standard for high-end joint motors.
· Permanent-magnet vernier machines (PMVM): low-speed high-torque, higher magnetic-circuit utilization.
· Rare-earth-free motors (synchronous reluctance, induction, electrically excited): may capture part of the market in low-cost models, but torque density is unlikely to match NdFeB in the short term.
3. Smart sensing and magnetic-circuit digitization
· 24-bit magnetic encoders will replace 16–20-bit as the high-end standard.
· TMR sensors, 3D magnetic sensors with higher integration.
· Digital twins + AI simulation for magnetic-circuit design optimization.
4. Additive manufacturing and miniaturization
3D-printed soft magnetic composite (SMC) motors and additively manufactured Halbach circuits will further unleash design freedom. Micro-robots (<1 cm scale) will require micro magnets.
5. Green manufacturing and recycling
EU new battery regulation, carbon border tax (CBAM) drive rare-earth recycling. Magnet manufacturers must establish "cradle-to-cradle" green supply chains.
6. Domestic substitution accelerates
Chinese humanoid robot companies (Unitree, AgiBot, Fourier, UBTech, Accelerating Evolution) are rising rapidly. Domestic magnet supply chains will capture historic opportunities.
Q1: How many magnets does one humanoid robot use?
A: A typical 30–50 servo joints + 20–40 magnetic encoders + multiple sensor magnets, corresponding to 2–5 kg of sintered NdFeB, with total magnet-system value USD 200–500.
Q2: Why is the Halbach array the first choice for high-end joint motors?
A: Halbach arrays increase air-gap flux density by 25–40% while significantly reducing back-iron leakage. Higher torque density in the same volume, or smaller magnet usage at the same torque — critical for size-constrained joint motors.
Q3: What is the smallest finger-joint magnet currently in volume production?
A: The industry is in volume production of OD 18 mm Halbach rotors, 2–4 poles, axial 8–15 mm, N40UH grade, torque density 25–40 kN·m/m³.
Q4: How to choose between bonded and sintered magnets in robots?
A: Bonded NdFeB for complex shapes and lower magnetic-performance requirements (encoder rings, sensor magnets, low-cost hub motors). Sintered NdFeB for all high-torque joint motors. They are complementary, not substitutes.
Q5: What is the typical operating temperature for joint-motor magnets?
A: Continuous 80–120°C, peak 150°C. N40UH/N42SH at 150°C have irreversible demagnetization <5%, currently the optimal choice.
Q6: What is the typical monthly production capacity for joint-motor magnet assemblies in the industry?
A: Mature suppliers can achieve 10,000+ joint-motor magnet assemblies per month, 100,000+ encoder magnet rings per month, and 5,000+ hub-motor rotors per month.
Q7: What are typical minimum order quantities (MOQ)?
A: Samples from 5–10 pieces, mass production from 100 pieces. Some suppliers support small-batch rapid delivery.
Q8: Can axial-flux motor rotors use Halbach arrays?
A: Yes. Axial-flux motor rotors (disc-type Halbach, OD 50–300 mm) are already applied in robot joints, e-motorcycles, and quadruped robots, delivering significantly higher torque density than conventional radial designs.
Q9: Are there baseline reference designs available for humanoid joint Halbach magnet assemblies?
A: Several specialized magnetic-assembly manufacturers offer baseline reference samples (finger-joint type, shoulder-joint type, knee-joint type) as starting points for customer design, reducing upfront validation cost.
Q10: What is the impact of humanoid mass production on the magnet industry?
A: 1 million annual shipments correspond to 30,000–50,000 tons of new NdFeB demand per year. The industry is scaling up production to meet this demand; high-end magnet-assembly capacity is expected to double by 2027.
Permanent magnets are a core strategic material of the robotics industry. From 28-joint humanoids to 6-axis industrial arms, from warehouse AGVs to surgical robots, from drones to deep-sea ROVs, magnets are everywhere.
Over the next 5–10 years, humanoid mass production will ignite magnet demand, new motor technologies (axial flux, Halbach, PMVM) will continue to evolve, domestic substitution will accelerate, and green manufacturing will become mandatory. The magnetic-assembly industry is scaling up rapidly to meet this historic demand surge.
For magnet selection technical support, custom solution consultation, or sample requests, please feel free to reach out.
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