OEM" Customized Magnetic Rotors
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FAIZEAL
OEM Custom Sleeve-Retained SPM Rotor
Surface-Mounted NdFeB, Segmented Arc Magnets, Carbon-Fiber Composite Sleeve — Built for Your High-Speed Servo Motor
Robotics | CNC Servo | Aerospace Actuator | Machine Tool | Vacuum / ATEX on Request
CUSTOM SLEEVE-RETAINED SPM ROTOR
Surface-Mounted NdFeB, Carbon-Fiber Sleeve, Lightweight Spider Hub — Built for High-Speed Servo
The rotor shown on the cover is a sleeve-retained, surface-mounted permanent magnet (SPM) rotor — the rotor half of a high-performance brushless servo motor or permanent-magnet synchronous motor (PMSM). The NdFeB magnet ring is segmented into individual arc-shaped poles, each independently magnetized in the tangential direction. The magnets are not exposed. They are retained by a thin, high-strength sleeve — typically a carbon-fiber composite wrap, alternatively Inconel 718 or stainless steel — that develops a uniform hoop stress around the magnet ring and lets the rotor run at speeds far beyond what a glued or banded magnet array would survive.
The hub is a machined spider-spoke design with lightening pockets between the central bore and the magnet rim. The pockets cut rotational inertia (J) without sacrificing torsional stiffness, so the rotor accelerates faster, decelerates faster, and the position loop in your drive closes faster. The combination — segmented NdFeB, sleeve retention, spider hub — is the architecture that high-end servo, robotics, and aerospace actuator manufacturers have converged on for the 6 kW - 30 kW peak, 8,000 rpm - 30,000 rpm class of brushless motor.
This is a custom-engineered build, not a catalog part. Every dimension — pole count, magnet grade, sleeve material and thickness, hub geometry, bore diameter and tolerance, stack length, balance grade — is sized to your stator, your drive, your duty cycle, and your service environment. We make one rotor at a time, to one set of customer drawings.
The magnet ring is built from sintered NdFeB (neodymium-iron-boron) arc segments — individually machined to your pole geometry. Each pole is a discrete piece, not a continuous ring. This gives you three engineering controls:
• Pole-by-pole material grade: each arc segment can be drawn from a specific magnet lot. We can match magnet lots pole-by-pole for minimum spread in flux density, or we can use a single lot for the entire ring if uniformity is sufficient
• Pole-arc optimization: each arc segment has a specific arc angle (pole-arc-to-pole-pitch ratio). We can skew the pole arcs, vary the pole-arc ratio along the ring, or use an asymmetric pole-arc profile to shape the back-EMF waveform and minimize cogging torque
• Magnet grade selection: N35 to N52 (SH / UH / EH for high-temperature; SmCo for sustained >200°C duty). We select the grade to your flux-density target and your operating temperature budget
For a 10-pole / 12-slot or 12-pole / 9-slot fractional-slot servo, the magnet segments are typically tangential-magnetization arcs. For a 4-pole or 6-pole low-speed servo, they can be radial-magnetization segments. The choice is part of the stator-pair design conversation we have with you at quotation stage.
The hub is the structural backbone of the rotor. It holds the magnet ring concentric, transfers torque to the shaft, and defines the rotor's inertia budget. The spider-spoke architecture with lightening pockets — visible as the elongated cavities between the bore and the magnet rim — gives the optimal engineering trade-off:
• Low inertia: the pockets cut as much mass as possible without losing structural stiffness. Rotational inertia (J) drives the motor's acceleration envelope. For a given torque, lower J means higher acceleration. For robotics and CNC axis servos, the inertia ratio between rotor and load determines the achievable acceleration
• High torsional stiffness: the radial spokes between the pockets transfer torque from the magnet ring to the shaft. The spoke geometry is sized to your torque envelope — more spokes for higher torque, fewer spokes for lower inertia
• Concentricity retention: the hub is the reference surface for the magnet ring. Machined in a single setup on a precision lathe or machining center, the hub sets the rotor's TIR (total indicated runout) to typically within 0.02 mm. This is the geometric datum your stator's air gap relies on
• Material selection: 7075-T6 aluminum (standard, high strength-to-weight); 6061-T6 aluminum (cost-optimized); 17-4PH stainless (high-temperature / vacuum); titanium Ti-6Al-4V (aerospace / weight-critical). We match the material to your duty cycle
For a customer with a very specific stack-length-to-OD ratio, we engineer the spoke pattern to that geometry. For a customer with a fixed shaft interface (press-fit, spline, keyed), we machine the bore to that interface and verify concentricity to your spec.
A brushless servo rotor's torque output is set by three coupled engineering quantities: the air-gap flux density (B), the stator current (I), and the synchronous electromagnetic coupling between them (the torque equation T = k . B . I for a well-designed motor). Understanding each one is what lets you specify a rotor that hits your motor's torque-speed envelope.
• Air-gap flux density (B): set by the magnet grade, the magnet arc geometry, the sleeve wall thickness, and the air gap. Higher-grade magnets (N48, N50, N52) push more flux into the gap. Tighter sleeve tolerances push the magnet closer to the air gap. We design the magnet array and the sleeve grinding spec together to hit your B target
• Stator current (I): not part of the rotor spec, but the rotor must be able to handle the stator's continuous and peak current without saturating or heating the magnet array. We verify the magnet grade and the rotor back-iron geometry against your stator's current envelope
• Synchronous coupling: the rotor magnet ring's pole count must match the stator's slot count to deliver smooth torque. A 10-pole rotor / 12-slot stator pairing (fractional-slot concentrated winding) gives low cogging and high winding factor. We pair the pole count to your stator's slot count at quotation stage
The rotor is the magnet side of the magnetic circuit. The stator is the current side. We work with your stator designer (or we spec a stator to our rotor) to deliver a motor that hits its torque-speed envelope without saturating, without cogging, and without thermal runaway.
The rotor is built end-to-end in our factory. The steps that define performance are not outsourced:
• Sintered NdFeB (and SmCo) production, grain-boundary diffusion, and pulse magnetization through controlled, audited supply chains
• Multi-axis grinding of magnet arc segments: tangential / radial magnetization geometry matched to your pole spec; arc dimension tolerance +/-0.02 mm; pole-arc angle +/-0.5 degree
• Magnet anti-corrosion plating: NiCuNi (standard) or epoxy / parylene coating for harsh environments
• Hub machining: 7075-T6 / 6061-T6 aluminum or 17-4PH stainless or titanium; CNC spider-spoke pattern with lightening pockets; bore machined to H6 / H7 tolerance with concentricity to 0.02 mm TIR
• Magnet ring assembly: arcs laid out and bonded in the hub / back-iron, magnetized, with end-to-end field mapping for flux-density uniformity
• Retention sleeve: carbon-fiber composite winding and cure (in-house); or Inconel 718 interference-fit and weld (in-house); or stainless-steel interference-fit (in-house)
• Sleeve OD grinding: precision cylindrical grinder; sleeve OD matched to your air-gap spec (typically Ra 0.4 um or better, concentricity 0.02 mm TIR)
• Dynamic balance: ISO 1940 Grade G2.5 (standard) or G1.0 (high-speed); balancing by precision sleeve OD grinding; final balance report with per-rotor vibration spectrum
• 100% final test on every rotor: Hi-Pot test (insulation integrity); insulation resistance; magnet ring integrity; sleeve OD concentricity; balance report; visual inspection
All values are typical ranges — every parameter is customized on request.
Parameter |
Typical Range / Customization |
Rotor Topology |
Surface-Mounted Permanent Magnet (SPM); segmented arc magnets; sleeve-retained |
Pole Count |
Customer-specified: 8 / 10 / 12 / 14 / 16 / 20 poles (typical for 8-30 kW class servos) |
Magnet Grade |
Sintered NdFeB; N35 / N38 / N42 / N48 / N50 / N52 (SH / UH / EH for high-temperature) |
Magnet Configuration |
Tangentially magnetized arc segments; individual pole pieces; matched to stator slot count |
Magnet Segment Tolerance |
+/-0.02 mm arc dimension; +/-0.5 degree pole-arc positioning |
Retention Sleeve |
Carbon-fiber composite wrap (standard for >8,000 rpm); Inconel 718 (high-speed / high-temp); 304 / 316 stainless (economy) |
Sleeve Wall Thickness |
0.5 - 1.5 mm (carbon-fiber composite); 0.3 - 1.0 mm (Inconel); matched to magnet hoop-stress envelope |
Sleeve Working Speed |
Up to 30,000 rpm continuous (CF sleeve, magnet-grade dependent); 50,000+ rpm on request |
Hub Material |
7075-T6 aluminum (standard, low-inertia); 6061-T6 aluminum (cost-optimized); 17-4PH stainless (high-temp / vacuum); titanium (aero / weight-critical) |
Hub Architecture |
Spider-spoke pattern with lightening pockets (standard); custom spoke geometry per stack length |
Central Bore |
Customer-specified diameter and tolerance; H6 / H7 press-fit; keyed or spline on request |
Bore Concentricity |
Within 0.02 mm TIR to magnet OD (sleeve-OD reference) |
Stack Length |
Customer-specified: 20 mm - 200 mm+; matched to torque envelope and inertia budget |
OD Range |
50 mm - 300 mm (standard); up to 500 mm on request (large frame servo / direct-drive) |
L/D Aspect Ratio |
0.3 - 0.7 (short-stack / pancake) typical for high-acceleration servo; 0.8 - 1.5 (long-stack) for high-torque / low-speed |
Dynamic Balance |
ISO 1940 Grade G2.5 (standard); G1.0 (high-speed); G6.3 (large-frame / low-speed); balancing by precision sleeve OD grinding |
Maximum Operating Speed |
8,000 - 30,000 rpm continuous (sleeve-retained); 50,000+ rpm on engineering review |
Continuous Torque Density |
Up to 25-40 kN.m/m^3 (sintered NdFeB, water-cooled stator side; matched stator stack) |
Peak Torque Capacity |
Up to 4x - 6x continuous for short transients (<2 sec) |
Working Temperature (Rotor) |
-40°C to +150°C (N-grade NdFeB); +200°C (EH); +350°C (SmCo optional) |
Surface Treatment |
Black epoxy / parylene sleeve coating (corrosion resistance); Ni / NiCuNi (magnet anti-corrosion) |
Magnet Anti-Corrosion |
NiCuNi plating (standard); epoxy / parylene (humid / marine / outdoor); on-magnet coating |
Encoder / Resolver Mounting |
Optional integrated resolver ring, encoder magnet ring, or sensor target on rear face |
Shaft Interface |
Press-fit (H6/H7) / interference bond (Loctite-grade adhesive) / keyed (DIN 6885) / spline |
Compliance / Documentation |
Material cert (NdFeB lot, hub, sleeve); Hi-Pot report; balance report; magnet lot traceability |
Production Traceability |
Per-rotor serial number; full material and process record; 10-year file retention |
1. 10 years of magnet-component engineering — NdFeB, SmCo, Halbach arrays, magnetic couplings, and now full rotor assemblies. We do not subcontract magnetic know-how
2. Custom is our default — every rotor is built to your pole count, your stack length, your bore, your sleeve spec. We do not sell catalog rotors
3. SPM, Halbach, and spoke-type IPM all in-house — we build all three rotor topologies and will tell you honestly which one fits your motor envelope
4. Sintered NdFeB (and SmCo) magnet lots in-house — N35 to N52, ground to your pole-arc spec, magnetized, and field-mapped per rotor
5. Carbon-fiber composite, Inconel, and stainless-steel sleeves in-house — sleeve material and thickness matched to your speed envelope
6. 7075 / 6061 aluminum, 17-4PH stainless, titanium hubs in-house — material and spoke geometry matched to your torque and inertia budget
7. ISO 1940 G2.5 / G1.0 / G6.3 balance in-house — every rotor dynamically balanced before shipment, with balance report
8. Drive-agnostic and stator-agnostic — we build the rotor, you bring the stator and the drive. We work with your existing stator or we spec a stator to our rotor
9. Export-ready documentation — CE / REACH / RoHS; per-rotor serial number; full material and process traceability; 10-year file retention
A sleeve-retained surface-mounted permanent magnet (SPM) rotor is a brushless servo motor rotor where the NdFeB magnet ring is on the surface of the rotor (not buried inside the lamination stack) and is held in place by a thin, high-strength sleeve that develops hoop stress around the magnet ring. The sleeve lets the rotor run at high speeds — 8,000 rpm to 30,000 rpm continuous (magnet-grade and sleeve dependent) — without the magnets flying off. Sleeve materials in production at FAIZEAL: carbon-fiber composite (standard), Inconel 718 (high-speed / high-temperature), 304 / 316 stainless steel (economy).
At high speed, an SPM rotor's magnets experience outward centrifugal force. Glued magnets fail at moderate speed (the glue degrades under shear). Banded magnets (steel wire wrap) work at moderate speed but the band adds inertia and eddy-current loss. A sleeve — particularly a carbon-fiber composite sleeve — develops uniform hoop stress around the entire magnet ring at any speed, adds negligible inertia, is non-magnetic (does not affect the magnetic circuit), and is non-conductive (does not induce eddy-current loss). The sleeve is the engineering decision that lets SPM scale to high-speed servo. For high-temperature (>200°C) or vacuum service, we use Inconel 718 instead of carbon-fiber.
Pole count is paired with the stator slot count, the stator winding topology, and the motor's torque-speed envelope. Common pairings: 10-pole rotor / 12-slot stator (fractional-slot concentrated winding, low cogging, high winding factor); 14-pole / 12-slot; 8-pole / 9-slot (fractional-slot, very low cogging); 4-pole / 6-slot (integer-slot, simpler winding, higher cogging). Tell us your stator's slot count and winding topology, and we will recommend the pole count that minimizes cogging and maximizes winding factor.
An SPM (surface-mounted permanent magnet) rotor has the magnet ring on the rotor surface. The rotor has no iron teeth to support the magnetic load. The result is the highest air-gap flux density and the lowest rotor inertia available in a synchronous motor. SPM is the standard for high-acceleration servo, robotics, and aerospace actuators. An IPM (interior permanent magnet) rotor has the magnets buried inside the rotor lamination stack. IPM gives additional reluctance torque (in addition to magnet torque) and allows field-weakening for a wider constant-power speed range. IPM is the standard for EV traction and industrial drives that need to run at 3x base speed. The choice between SPM and IPM is a stator-pair design decision; tell us your duty cycle and we will recommend the right topology.
Tangential magnetization means the magnet is magnetized parallel to the rotor circumference (the magnet's long axis is tangential). Tangential magnetization gives higher air-gap flux density than radial magnetization at the same magnet volume. It is the standard for high-torque servo. Radial magnetization means the magnet is magnetized perpendicular to the rotor circumference (pointing outward). Radial magnetization gives a more sinusoidal air-gap flux distribution, which can reduce cogging in some stator pairings. Tangential is the standard for SPM servo; radial is the standard for low-speed high-pole-count machines (wind turbine generators, large direct-drive motors).
Yes. Samarium-cobalt (SmCo) gives sustained operation up to +350°C (vs +150°C for N-grade NdFeB) and is more corrosion-resistant than NdFeB (no plating required for most service environments). The trade-off is energy product: SmCo has roughly 60-70% of the energy product of N-grade NdFeB at the same volume, so you need a larger magnet ring to hit the same flux-density target. SmCo is the right choice for high-temperature rotor service (downhole tools, aerospace actuators, high-temperature turbomachinery). We will spec the SmCo grade to your flux and temperature budget.
With a carbon-fiber composite sleeve and N-grade NdFeB magnets, the typical continuous speed limit is 8,000 rpm - 30,000 rpm depending on the magnet grade, the sleeve wall thickness, and the rotor OD. With Inconel 718 sleeves and N-grade NdFeB, the limit can exceed 30,000 rpm continuous. With SmCo magnets and Inconel sleeves, 50,000 rpm+ is feasible. The sleeve wall thickness is sized to your maximum continuous speed and the magnet hoop-stress envelope. We return a feasibility note and a recommended sleeve spec within 2 working days.
Standard OD range is 50 mm - 300 mm. We have built rotors up to 500 mm OD for large-frame servo and direct-drive wind applications. Above 500 mm OD, the magnet ring handling and sleeve winding become engineering-specific; we will review the application and return a feasibility note within 2 working days.
Dynamic balance is achieved by precision grinding of the sleeve outer diameter (the magnetically active surface). Sleeve-OD grinding gives balance correction in micron-precision radial cuts, with no balance weights and no balance holes — preserving the rotor's geometry and concentricity. Final balance grade is ISO 1940 G2.5 (standard), G1.0 (high-speed servo), or G6.3 (large-frame / low-speed). Every rotor ships with a balance report showing residual unbalance and vibration spectrum.
We can integrate an encoder magnet ring, a resolver target ring, or a sensor mount surface on the rear face of the rotor (the face opposite the magnet ring). Common integrations: Hall-sensor magnet ring (3-pole pair, sin/cos or digital output); resolver target (variable-reluctance or magnetized); incremental encoder target (optical or magnetic); absolute encoder target (BiSS / EnDat / SSI / SSI24 / Hiperface). Tell us your encoder / resolver spec and we will integrate the target to your drawing.
Standard interface is interference press-fit at H6 / H7 tolerance. We machine the bore to your specified diameter and tolerance, and verify concentricity to the magnet OD within 0.02 mm TIR. For zero-backlash applications (precision servo), we bond the rotor to the shaft with a Loctite-grade structural adhesive. For high-torque applications, we add a keyway (DIN 6885) or a spline. For frequent service or field-replaceable assemblies, we can machine a tapered bore or a bolted flange interface. Tell us your shaft interface and we will match it.
Prototype / sample rotor: 15-25 working days after drawing freeze. Production: 30-60 working days depending on volume, materials, and pole count. Sleeve-retained rotors with carbon-fiber composite sleeves typically run on the shorter end of this range; Inconel-sleeved and large-OD rotors may run longer. Repeat orders from a frozen design typically ship in 20-40 working days.
Yes. Send us your existing rotor (or its drawings, or its CAD model, or its magnetic field map), and we will reverse-engineer the pole count, the magnet grade, the sleeve spec, the hub geometry, and the bore. We will return a quote for an exact-replacement rotor (drop-in replacement on your existing shaft) or for a performance-upgraded rotor (higher energy product, better sleeve, lower inertia) within 2 working days. We support replacement of OEM rotors from Kollmorgen, Parker, Yaskawa, Estun, Faulhaber, Maxon, Teknic, and most other brushless servo manufacturers.
Yes. We offer scheduled batch-rotation stock for OEM customers, with a 5-year material and process reproducibility guarantee per fleet reference. Tell us your expected service interval and your safety stock target, and we will hold the right number of finished rotors in our bonded warehouse for call-off.
Send us:
• Rotor OD and stack length (or your existing motor's dimensions)
• Pole count and stator slot count (or we will recommend, based on your duty cycle)
• Magnet grade (N35-N52 / SH / UH / EH / SmCo) — or let us specify to your flux target
• Sleeve material preference (carbon-fiber composite / Inconel 718 / stainless steel) — or let us recommend to your speed envelope
• Hub material preference (7075-T6 Al / 6061-T6 Al / 17-4PH stainless / titanium) — or let us recommend
• Bore diameter and tolerance (H6 / H7 / keyed / splined / bonded) — or we will spec to your shaft drawing
• Maximum continuous speed and peak speed
• Working temperature range (rotor-side)
• Dynamic balance grade (G2.5 / G1.0 / G6.3)
• Encoder / resolver target mounting requirements (or we will spec to your drive)
• Surface treatment (black epoxy / parylene / Ni / NiCuNi)
• Service environment (clean room / ATEX / oil & gas / aerospace / vacuum)
• Quantity and target delivery date
We typically return a feasibility and indicative pricing note within 2 working days, and a firm quotation within 5-7 working days.
FAIZEAL — custom sleeve-retained SPM rotors, segmented NdFeB, sleeve material matched to your speed envelope, built to your pole count, stack length, and bore.
