AFPM Motor Bearing Selection: Calculator & Guide

References [1]–[6] are linked in the source register. Every numerical example on this page is illustrative unless a source is explicitly named.

The screen assumes uniform normal flux over the pole-covered annulus: A = π(Dₒ² − Dᵢ²)/4, p = αₚB²/(2μ₀), F = pA, with diameters converted to metres. For 260/160 mm, 0.85 T and αₚ = 0.75, p ≈ 215.6 kPa = 21.56 N/cm² and F ≈ 7,112 N per gap. This uses peak B as a uniform field approximation; a spatial field integral is needed for a real machine. [1]

Illustrative Figure 2: Dual-Rotor Unbalanced Magnetic Pull (UMP) Under Tolerance Offset Δg

The table below describes the implemented screening model. Bearing examples are synthetic teaching data; no manufacturer rating, matched-pair certification, speed approval or fit recommendation is implied.

The application runs synchronously in your browser; edits immediately update the screen. Invalid or missing fields withhold results. A boundary message provides a static-check or structural-review path when the model cannot produce a meaningful result.

Width describes the illustrative bearing element, not the full paired support envelope. Pair load sharing, induced thrust and mounting stiffness are unresolved. Obtain a supplier calculation with the exact designation, suffix, lubrication, fits and operating temperatures before ordering.

The calculator estimates support tilt only. A small number can coexist with unacceptable axial shaft motion, rotor-disc bending, magnet height variation or preload loss. Add those terms with tolerances and measured hot/cold runout to form a minimum-gap budget. Do not interpret the green band as a rotor-clearance approval.

For the illustrative aluminium/steel stack, 100 mm span and 60 K rise give ΔL = (23−11.5) × 10⁻⁶ × 100 × 60 = 0.069 mm. An assumed 30 N/mm spring changes force by 2.07 N over that travel. This is an arithmetic example, not a guarantee of constant preload: spring travel, relaxation, thermal gradients and support stiffness remain to be checked.

Rigid setting can improve stiffness but magnifies dimensional errors. A compliant setting can absorb growth while reducing axial restraint. Heating and cooling are both modeled; the sign for a real assembly depends on locating shoulders, ring temperatures and the DB/DF stack. Request preload-versus-temperature and drag-torque measurements rather than transferring the simplified sign rule directly to production.

Illustrative Figure 3: Inverter dv/dt Capacitive Coupling & Bearing Current Fluting Mechanism

PWM common-mode excitation can couple into the rotor and discharge through lubricant films. Insulation, grounding and shielded cabling address different paths. SKF explains why the complete motor, inverter, cables and load must be considered together. The fixed voltages in the schematic are illustrative; they are not measured AFPM thresholds. [5]

Basic L10h excludes electrical erosion, wear and corrosion. Lubricant selection needs operating viscosity, contamination, bearing temperature, load and ndm = n(d+D)/2. Use the supplier viscosity chart and lubrication-life method; this page does not calculate κ, grease life or a relubrication interval. [2]

The calculator always compares speed to its assumed grease ceiling. Selecting ceramic electrical protection does not select oil lubrication or authorize higher speed. Oil feed, seals, churning loss and cooling must be designed and verified as a system.

Public model names do not establish an internal bearing bill of materials. No verified teardown or OEM bearing drawing is available in this page’s evidence set for EMRAX 228, YASA 750/P400, Magnax AXF275, Saietta AFT140 or Koenigsegg Quark. Their contact angles, preload packs and electrical protection are therefore unknown / pending OEM confirmation. The calculator scenarios are independent teaching examples, not reconstructions of these motors.

For sourcing, request bearing designations and matched-set ratings, permitted shaft loads, continuous/peak duty, preload procedure, grease specification and electrical mitigation evidence. Compare warranty and maintenance conditions as well as quoted component cost.

Illustrative Figure 5: Complete AFPM Bearing Selection & Preload Engineering Decision Tree

The diagram is a planning workflow. Passing its illustrative tilt and fatigue checks does not authorize release. Agree drawing-specific fits, geometric tolerances and acceptance limits with the bearing supplier. ISO 21940-11 covers rigid-rotor balancing procedures; a universal G1.0 requirement cannot be inferred from an AFPM rotor speed alone. [6]

1. Calculate steady, peak and stationary loads, minimum loads and supplier static safety factors under ISO 76. [3]
2. Resolve internal contact distribution, clearance and misalignment using a supplier method. ISO 16281:2025 replaces the withdrawn 2008 technical specification; its modified-life method has specific hybrid-bearing limitations. [4]
3. Measure drag torque and axial compliance at defined loads and temperatures; calibrate acceptance limits on qualified units.
4. Measure assembled hot/cold air gaps, runout and vibration under the intended duty. A generic vibration or megohmmeter limit is insufficient to prove bearing health or high-frequency electrical protection.
5. Confirm current paths, lubrication, seals, balance, manufacturing capability and maintenance terms before design sign-off.

Published 2026-10-23; reviewed 2026-10-23. Review these methods and sources every six months, next due 2027-04-23, or earlier when a cited standard or supplier method changes.

Send rotor geometry, magnetic force/FEA data, air-gap budget, shaft drawing, peak and continuous loads, duty spectrum, temperatures, inverter/cable details, target reliability and maintenance requirements. Treat all calculator numbers as preliminary assumptions until the supplier confirms ratings and the assembly passes validation.