What does the LCM result mean?

It is the slot/pole repeat count per mechanical revolution. A higher LCM is often a better first-pass sign because cogging events are spread across more smaller periods, but it is not a guarantee of low measured cogging.

Why did the page remove the phrase optimal skew angle?

The calculator can provide sweep references, but final skew depends on winding factor, magnet arc, leakage, saturation, and manufacturability. Calling a slot or pole pitch automatically optimal would overstate the calculation.

What should I do with a boundary warning?

Keep the result, but treat it as a review flag. Add at least one alternate slot/pole candidate and require FEA before procurement or tooling decisions.

Can I use odd pole counts?

No. The calculator expects physical north/south pole pairs, so rotor poles must be even.

Is fractional slot always better?

No. Fractional-slot combinations can reduce cogging risk, but they can also affect winding factor, space harmonics, noise, and losses. Use them as candidates, not as automatic winners.

When should I choose magnet skew instead of stator skew?

Magnet skew is often more practical in AFPM layouts when stator skew would complicate core tooling or winding. It shifts complexity to rotor assembly, fixture accuracy, and magnet edge validation.

How does SMC change the mitigation options?

SMC can form 3D tooth features and segmented shapes that are hard to stamp from laminations. The tradeoff is that density, permeability, insulation, and mechanical strength must be controlled by the supplier.

Does cogging reduction always reduce torque?

Not always, but many methods trade some average torque, back-EMF, or manufacturing simplicity for lower ripple. The validation sweep should track both cogging torque and useful torque output.

What evidence should be in a supplier quote?

Ask for material data, geometry tolerance, proposed mitigation method, inspection plan, and how the supplier will prove the no-load torque target.

What is the minimum prototype test?

A controlled back-drive measurement with no current, known bearing preload, torque sensor range, fixture inertia note, and angular resolution high enough to capture the predicted cogging period.

Should cogging torque be separated from loaded torque ripple?

Yes. Cogging torque is measured without current and comes from geometry and magnet interaction. Loaded torque ripple can come from current control, saturation, winding harmonics, and inverter effects.

When is public evidence insufficient?

Published papers support method selection, but they rarely match your exact slot/pole count, SMC grade, magnet arc, air gap, bearing stack, and production tolerance. Mark those items as assumptions until tested.

Hybrid calculator + engineering report

AFPM Core Cogging Torque Reduction

Screen slot/pole combinations, interpret cogging periods, and decide whether skew, magnet shaping, or SMC tooth geometry should move into 3D FEA and supplier review.

Reviewed July 25, 2026Tool-first hybrid pageFEA required for release

Run calculator Review validation gates

Decision boundary

This page supports early AFPM core concept screening. It does not replace 3D electromagnetic simulation, production tolerance analysis, or measured prototype torque ripple.

AFPM Cogging Torque Screening Calculator

Screen slot/pole combinations, cogging repeat periods, and skew-sweep reference angles before 3D FEA. Results are topology guidance, not final electromagnetic sign-off.

Stator Slots (Qs)

Screening range: 3-180 whole slots.

Rotor Poles (2p)

Must be even. Screening range: 2-120 poles.

Phases (m)

Common AFPM screens use 3 phases; this field allows non-standard early studies.

Calculated results

Mechanical angles are first-pass references for topology and skew sweeps.

LCM(Slots, Poles)60

GCD(Slots, Poles)2

Slots per pole per phase (q)0.400

Cogging periods / mech rev60

Fundamental cogging period6.00 deg mech

Slot pitch reference30.00 deg mech

Pole pitch reference36.00 deg mech

How to use the skew references

Start skew and magnet-arc sweeps around the cogging period, then bracket with slot-pitch and pole-pitch references. The lowest cogging point must still be confirmed with 3D FEA, winding factor, magnet segmentation, and prototype back-drive data.

High LCM / Fractional Slot

The fractional-slot combination has a high cogging repeat count, which is a useful first-pass indicator for lower fundamental cogging components.

Keep the topology in the shortlist, then validate skew, magnet arc, and tooth shoe geometry with 3D FEA and prototype torque ripple data.

Use this screen to shortlist candidate slot/pole sets, not to approve final tooling.

Request engineering review

Tool result first, evidence second

The calculator answers the immediate slot/pole question. The report then explains how to act on that answer: what to compare, where it can fail, and which validation gate comes next.

Turn Calculator Results Into Actions

Use the result status to decide whether to keep, compare, or reject a topology before spending FEA and prototype budget.

Result status	Meaning	Next action	Owner
Integral q	Slotting and pole symmetry are more likely to reinforce cogging harmonics.	Add a fractional-slot candidate and do not release tooling from this topology alone.	Motor design
Fractional q, LCM < 60	Better than integral q, but repeat count is still low enough to leave visible no-load ripple.	Sweep cogging-period skew, magnet arc, and tooth-shoe relief before supplier RFQ.	EM + DFM
Fractional q, LCM >= 60	Good first-pass topology for low cogging, but not proof of low torque ripple.	Shortlist for 3D FEA, then validate with prototype torque-speed data.	EM test
Boundary warning	The calculator accepts the input, but q, GCD, or cogging period exposes a special risk.	Document the warning in the design review and require an alternate concept.	Program lead

Key Conclusions

These are the decision statements the page supports. Each one is tied to a source ID or an explicit limitation.

LCM screens topology risk before FEA

A higher LCM between stator slots and rotor poles increases the number of cogging periods per mechanical revolution. That usually spreads cogging energy over more cycles and is a practical first screen for smoother low-speed behavior.

Evidence: Supported by AFPM cogging-reduction review methods and the calculator formula used on this page. [S1]

Skew is a sweep variable, not an automatic optimum

Slot pitch, pole pitch, and cogging-period angles are useful sweep references. They should not be labeled as final optimum skew angles without winding-factor, magnet, and 3D leakage effects.

Evidence: Cost-effective stator modification literature and AFPM review papers describe skew and tooth-shape changes as tradeoff studies. [S1, S2]

SMC cores move mitigation into tooth geometry

Soft magnetic composite cores can support net-shape tooth shoes, local chamfers, closed-slot concepts, and 3D flux paths that are difficult to stamp as one-piece laminations.

Evidence: Use as a manufacturing design option, with material data and structural validation checked before RFQ award. [S4, S5]

Magnet arc and segmentation can avoid stator retooling

Rotor-side mitigation can tune the air-gap permeance waveform while keeping the stator core closer to a repeatable manufacturing process.

Evidence: AFPM cogging-reduction reviews group magnet shaping, magnet skew, and magnet offset with stator geometry methods. [S1]

Prototype torque ripple remains the release gate

A low calculator risk score is only a shortlist signal. Release decisions still need no-load torque sweep, loaded torque ripple, air-gap tolerance, and back-drive measurement data.

Evidence: The calculator omits saturation, fringing, tooth-end leakage, magnet tolerances, bearing preload, and inverter-current effects. [S3, S4]

What The Angles Actually Mean

The page now separates three concepts that are often conflated: slot pitch, pole pitch, and the fundamental cogging period. They are useful sweep references, but the final setting must be chosen from simulation and measurement.

Release rule

If a supplier proposal only quotes a calculated skew angle, ask for the sweep plot that shows cogging torque, average torque, back-EMF, and manufacturability at the chosen point.

Scenario Examples

Use these examples to calibrate the calculator output before applying it to a proprietary topology.

12-slot / 10-pole / 3-phase

Common compact AFPM screen with fractional q = 0.400.

LCM is 60, so it is usually a credible first shortlist if winding factor and thermal limits are acceptable.

Next: Run FEA sweeps around cogging-period and magnet-arc changes.

12-slot / 8-pole / 3-phase

Integral q = 0.500? No; fractional but lower LCM than 12/10.

LCM is 24, so the page flags higher cogging-period amplitude risk despite a familiar slot count.

Next: Compare 12/10 or 18/16 before ordering hard tooling.

24-slot / 20-pole / 3-phase

Scaled version of a 12/10 family.

LCM doubles to 120 and cogging period halves, improving topology screen but raising winding, inspection, and cost complexity.

Next: Check tooth fill, phase balance, and compacted SMC density repeatability.

Slots equal poles

Sometimes proposed to simplify magnetic pitch intuition.

The calculator flags it because equal slot/pole counts can create strong preferred alignment positions.

Next: Reject as baseline unless a detailed harmonic and startup study proves otherwise.

Mitigation Method Matrix

Compare the method, use case, benefit, risk, and validation path before adding geometry complexity.

Method	Best for	Benefit	Risk	Validation
Fractional slot/pole selection [S1]	New topology selection before package freeze	Reduces harmonic alignment without adding parts	May reduce winding factor or introduce space harmonics	LCM/q screen, winding factor check, no-load FEA
Tooth shoe relief or chamfer [S1, S2, S5]	SMC or segmented stator cores with controllable tooth geometry	Smooths permeance change near slot openings	Can reduce average torque if air-gap flux is weakened too much	Parametric tooth-shoe sweep and compacting-tool review
Magnet arc tuning [S1]	Rotor-side iteration when stator tooling is fixed	Changes cogging harmonic content without changing stator core	Can raise magnet cost, edge demagnetization risk, and assembly error	FEA magnet-arc sweep and adhesive/fixture capability review
Rotor magnet skew or stagger [S1, S2]	AFPM layouts where stator skew is impractical	Offsets torque peaks across the active area	Can reduce effective torque and complicate balancing	Back-EMF, torque density, balance, and fixture studies
SMC closed-slot or 3D tooth profile [S4, S5]	Custom powder metallurgy core programs	Moves mitigation into net-shape core features	Requires B-H curve, density, insulation, and strength control	Material coupon, press-tool capability, and 3D FEA

Topology Levers

Slot/pole selection, q, winding factor, and LCM should be decided while package and winding layout are still flexible.

SMC Core Levers

SMC can support shaped teeth and segmented cores, but density, insulation, strength, and B-H data must be supplier-controlled.

Rotor Levers

Magnet arc, skew, and stagger can reduce cogging, but they move risk into magnet cost, adhesive fixtures, balance, and inspection.

Evidence Ledger And Limits

Public sources support method selection. Exact reduction percentages are not reused here unless the topology, material, and test setup match the reader's design.

ID	Source	Use on this page	Confidence / limit
S1	Cogging Torque Reduction Techniques in Axial Flux Permanent Magnet Machines: A Review Energies, 2024 · 2024-02-24	Classifies AFPM cogging mitigation methods such as slot/pole choice, skew, magnet shaping, and geometry modification.	High for method taxonomy; specific percentages require the original test setup.
S2	Cost-Effective Stator Modification Techniques for Cogging Torque Reduction in Axial Flux Permanent Magnet Machines IEEE ITEC-AP, 2018 · 2018-06	Supports treating stator geometry changes as practical mitigation candidates with cost and manufacturability tradeoffs.	Medium-high; conference scope, validate against current product constraints.
S3	Cogging Torque Computation and Optimization in Dual-Stator Axial Flux Permanent Magnet Machines Electrical Engineering in Japan, 2020 · 2020-08-14	Supports dual-stator AFPM cogging computation and optimization framing.	Medium-high for analysis workflow; exact design data depends on topology.
S4	AxialFluxCore AFPM Core Air Gap Design guide AxialFluxCore · July 25, 2026	Internal companion page for air-gap tolerance, flux-density screening, and validation caution.	High for same-site design workflow context.
S5	AxialFluxCore Technology Materials AxialFluxCore · July 25, 2026	SMC material and manufacturing context for tooth geometry, density, insulation, and supplier capability review.	High for AxialFluxCore RFQ context; material values still require supplier datasheets.

Validation Gates

Validation should get stricter as the design moves from a calculator result to purchased tooling. Each gate answers a different failure mode.

Gate	Question	Artifact	Failure mode
Topology screen	Does slot/pole/q/LCM justify keeping the concept?	Calculator result, winding factor estimate, harmonic notes	High cogging risk hidden by average torque target
3D no-load FEA	Does cogging torque stay within the application ripple band?	Torque vs mechanical angle sweep with mesh settings	2D or idealized model misses axial leakage and end effects
Loaded torque ripple	Does current excitation introduce ripple that dominates cogging?	Loaded torque map across speed/current points	Cogging is solved but load ripple or inverter harmonics remain
Manufacturing capability	Can the supplier repeat the tooth/magnet geometry?	Cp/Cpk plan, tooling datum drawing, inspection method	Prototype geometry is not repeatable in batch production
Prototype back-drive	Does measured no-current torque match the model?	Back-drive torque trace, fixture inertia note, bearing preload	Bearing drag or fixture error masks true cogging torque

Risk Controls

Cogging reduction can fail because the wrong evidence is used at the wrong decision point.

Risk	Impact	Signal	Mitigation
Over-trusting the calculator	Wrong topology selected before electromagnetic validation	Decision made from LCM/q only	Require 3D FEA and a second topology candidate before tooling.
Torque density loss from skew	Cogging improves while continuous torque target is missed	Skew is increased without winding-factor comparison	Track average torque, back-EMF, and ripple in the same sweep.
SMC material mismatch	Designed tooth shape cannot meet flux or thermal assumptions	Supplier quote lacks B-H curve, density, or insulation data	Request material coupons and use the same batch in prototype tests.
Rotor-side complexity	Magnet skew/stagger reduces cogging but creates assembly error	Magnet fixture datum is not specified	Tie magnet placement tolerance to measured torque ripple limits.

RFQ Checklist For Low-Cogging AFPM Cores

Send these items with the calculator result so suppliers can price the actual validation burden, not just a shaped part.

Slot count, pole count, phase count, winding layout, and target speed range

No-load cogging torque target with unit, measurement bandwidth, and temperature

Allowed mitigation methods: tooth relief, magnet arc, magnet skew, rotor stagger, SMC closed-slot concept

Material package: SMC grade, B-H curve, density window, insulation method, heat treatment, coating

Tolerance package: air gap, tooth datum, magnet position, stack flatness, runout, bearing preload

Validation package: FEA assumptions, prototype back-drive fixture, torque sensor range, pass/fail criteria

Review RFQ templates Send a cogging reduction brief

Frequently Asked Questions

Grouped around use, engineering decisions, and sourcing so the page supports both immediate calculation and deeper research.

Request Engineering Review

Convert a calculator result into a manufacturable AFPM core validation plan.

Slot/pole and harmonic shortlist review

SMC tooth geometry and material feasibility check

Prototype torque ripple measurement plan

Contact Engineering

AFPM Core Cogging Torque Reduction

Screen slot/pole combinations, interpret cogging periods, and decide whether skew, magnet shaping, or SMC tooth geometry should move into 3D FEA and supplier review.

Reviewed July 25, 2026Tool-first hybrid pageFEA required for release

Decision boundary

This page supports early AFPM core concept screening. It does not replace 3D electromagnetic simulation, production tolerance analysis, or measured prototype torque ripple.

Result status

Meaning

Next action

Owner

Integral q

Slotting and pole symmetry are more likely to reinforce cogging harmonics.

Add a fractional-slot candidate and do not release tooling from this topology alone.

Motor design

Fractional q, LCM < 60

Better than integral q, but repeat count is still low enough to leave visible no-load ripple.

Sweep cogging-period skew, magnet arc, and tooth-shoe relief before supplier RFQ.

EM + DFM

Fractional q, LCM >= 60

Good first-pass topology for low cogging, but not proof of low torque ripple.

Shortlist for 3D FEA, then validate with prototype torque-speed data.

EM test

Boundary warning

The calculator accepts the input, but q, GCD, or cogging period exposes a special risk.

Document the warning in the design review and require an alternate concept.

Program lead

What The Angles Actually Mean

Release rule

If a supplier proposal only quotes a calculated skew angle, ask for the sweep plot that shows cogging torque, average torque, back-EMF, and manufacturability at the chosen point.

Method

Best for

Benefit

Risk

Validation

Fractional slot/pole selection

[S1]

New topology selection before package freeze

Reduces harmonic alignment without adding parts

May reduce winding factor or introduce space harmonics

LCM/q screen, winding factor check, no-load FEA

Tooth shoe relief or chamfer

[S1, S2, S5]

SMC or segmented stator cores with controllable tooth geometry

Smooths permeance change near slot openings

Can reduce average torque if air-gap flux is weakened too much

Parametric tooth-shoe sweep and compacting-tool review

Magnet arc tuning

[S1]

Rotor-side iteration when stator tooling is fixed

Changes cogging harmonic content without changing stator core

Can raise magnet cost, edge demagnetization risk, and assembly error

FEA magnet-arc sweep and adhesive/fixture capability review

Rotor magnet skew or stagger

[S1, S2]

AFPM layouts where stator skew is impractical

Offsets torque peaks across the active area

Can reduce effective torque and complicate balancing

Back-EMF, torque density, balance, and fixture studies

SMC closed-slot or 3D tooth profile

[S4, S5]

Custom powder metallurgy core programs

Moves mitigation into net-shape core features

Requires B-H curve, density, insulation, and strength control

Material coupon, press-tool capability, and 3D FEA

Source

Use on this page

Confidence / limit

Cogging Torque Reduction Techniques in Axial Flux Permanent Magnet Machines: A Review

Energies, 2024 · 2024-02-24

Classifies AFPM cogging mitigation methods such as slot/pole choice, skew, magnet shaping, and geometry modification.

High for method taxonomy; specific percentages require the original test setup.

Cost-Effective Stator Modification Techniques for Cogging Torque Reduction in Axial Flux Permanent Magnet Machines

IEEE ITEC-AP, 2018 · 2018-06

Supports treating stator geometry changes as practical mitigation candidates with cost and manufacturability tradeoffs.

Medium-high; conference scope, validate against current product constraints.

Cogging Torque Computation and Optimization in Dual-Stator Axial Flux Permanent Magnet Machines

Electrical Engineering in Japan, 2020 · 2020-08-14

Supports dual-stator AFPM cogging computation and optimization framing.

Medium-high for analysis workflow; exact design data depends on topology.

AxialFluxCore AFPM Core Air Gap Design guide

AxialFluxCore · July 25, 2026

Internal companion page for air-gap tolerance, flux-density screening, and validation caution.

High for same-site design workflow context.

AxialFluxCore Technology Materials

AxialFluxCore · July 25, 2026

SMC material and manufacturing context for tooth geometry, density, insulation, and supplier capability review.

High for AxialFluxCore RFQ context; material values still require supplier datasheets.

Gate

Question

Artifact

Failure mode

Topology screen

Does slot/pole/q/LCM justify keeping the concept?

Calculator result, winding factor estimate, harmonic notes

High cogging risk hidden by average torque target

3D no-load FEA

Does cogging torque stay within the application ripple band?

Torque vs mechanical angle sweep with mesh settings

2D or idealized model misses axial leakage and end effects

Loaded torque ripple

Does current excitation introduce ripple that dominates cogging?

Loaded torque map across speed/current points

Cogging is solved but load ripple or inverter harmonics remain

Manufacturing capability

Can the supplier repeat the tooth/magnet geometry?

Cp/Cpk plan, tooling datum drawing, inspection method

Prototype geometry is not repeatable in batch production

Prototype back-drive

Does measured no-current torque match the model?

Back-drive torque trace, fixture inertia note, bearing preload

Bearing drag or fixture error masks true cogging torque

Risk

Impact

Signal

Mitigation

Over-trusting the calculator

Wrong topology selected before electromagnetic validation

Decision made from LCM/q only

Require 3D FEA and a second topology candidate before tooling.

Torque density loss from skew

Cogging improves while continuous torque target is missed

Skew is increased without winding-factor comparison

Track average torque, back-EMF, and ripple in the same sweep.

SMC material mismatch

Designed tooth shape cannot meet flux or thermal assumptions

Supplier quote lacks B-H curve, density, or insulation data

Request material coupons and use the same batch in prototype tests.

Rotor-side complexity

Magnet skew/stagger reduces cogging but creates assembly error

Magnet fixture datum is not specified

Tie magnet placement tolerance to measured torque ripple limits.

AFPM Core Cogging Torque Reduction

Calculated results

Tool result first, evidence second

Turn Calculator Results Into Actions

Key Conclusions

What The Angles Actually Mean

Scenario Examples

Evidence Ledger And Limits

Related Engineering Paths

Validation Gates

Frequently Asked Questions

Using the calculatorWhat does the LCM result mean?

Using the calculatorWhy did the page remove the phrase optimal skew angle?

Using the calculatorWhat should I do with a boundary warning?

Using the calculatorCan I use odd pole counts?

Engineering decisionsIs fractional slot always better?

Engineering decisionsWhen should I choose magnet skew instead of stator skew?

Engineering decisionsHow does SMC change the mitigation options?

Engineering decisionsDoes cogging reduction always reduce torque?

Validation and sourcingWhat evidence should be in a supplier quote?

Validation and sourcingWhat is the minimum prototype test?

Validation and sourcingShould cogging torque be separated from loaded torque ripple?

Validation and sourcingWhen is public evidence insufficient?

AFPM Core Cogging Torque Reduction

Calculated results

Tool result first, evidence second

Turn Calculator Results Into Actions

Key Conclusions

What The Angles Actually Mean

Scenario Examples

Evidence Ledger And Limits

Related Engineering Paths

Validation Gates

Frequently Asked Questions

Using the calculatorWhat does the LCM result mean?

Using the calculatorWhy did the page remove the phrase optimal skew angle?

Using the calculatorWhat should I do with a boundary warning?

Using the calculatorCan I use odd pole counts?

Engineering decisionsIs fractional slot always better?

Engineering decisionsWhen should I choose magnet skew instead of stator skew?

Engineering decisionsHow does SMC change the mitigation options?

Engineering decisionsDoes cogging reduction always reduce torque?

Validation and sourcingWhat evidence should be in a supplier quote?

Validation and sourcingWhat is the minimum prototype test?

Validation and sourcingShould cogging torque be separated from loaded torque ripple?

Validation and sourcingWhen is public evidence insufficient?