Add induction motor mode, fringing derate, and self-start check

[ecto]

Summary

Extends the motor analysis toolkit with two new capabilities: a thin-sheet axial induction machine model (for drag-cup and PCB-cage rotors) and a Carter-like fringing derate for permanent-magnet flux predictions. Adds a new check_self_start tool to answer the critical design question: will the motor overcome bearing friction and spin?

Key Changes

Induction Motor Mode (calc_motor mode: "induction")

• New calcMotorInduction() function implementing the Russell–Norsworthy thin-sheet induction closed form
• Computes fundamental gap field B1 from rotating MMF, torque-per-unit-slip (linear in slip), locked-rotor torque, synchronous speed, and rotor sheet dissipation
• Rust mirror in new crates/vcad-ecad-sim/src/induction.rs with full test coverage
• Schema updated to make PM-mode inputs conditional; induction mode requires phase_current_a, electrical_freq_hz, effective_gap_mm, sheet_conductance_s
• Optional end_effect_factor (default 0.65) models eddy-current return paths outside the active annulus

PM Mode Fringing Derate

• New fringing_derate() function in crates/vcad-ecad-sim/src/airgap.rs implements Carter-like pole-edge fringing: B_derated = B_raw · w/(w+2g)
• Opt-in via magnet.pole_width_mm in calc_motor; when provided, both raw MEC prediction and derated flux are reported and claimed
• Kt/Ke and speed–torque curve use the derated flux; raw value available for FEA grading
• Honest for pole width ≳ 2× gap; below that treated as a lower bound

New check_self_start Tool

• Answers "will it spin?" by comparing available standstill torque against bearing friction
• Accepts either direct available_torque_nm or computed from kt_nm_per_a × current_a
• Friction estimated from bearing catalog (presets: 608-2RS, 608-ZZ, 625, 688 with light/medium preload) or supplied directly
• Returns starts (fail-closed: beats worst-case friction), starts_best_case (beats optimistic end), and margin in mN·m
• Typical sealed 608-2RS pair: 1–4 mN·m; shielded and miniature variants an order of magnitude freer
• Demonstrates that thin-sheet induction machines (µN·m locked-rotor) require ultra-low-friction bearings to self-start

Implementation Details

• Induction model: First-order only — linear-in-slip torque (no breakdown peak), no stator leakage/magnetizing reactance, no slotting/saturation. Valid for will-it-spin sizing; not an FEA substitute.
• Fringing derate: Pure geometry ratio, first-order in gap/width. Mirrors Rust vcad_ecad_sim::airgap::fringing_derate.
• EM claims: Both induction and fringing derate report their predictions as EM receipt claims (method: "thin-sheet-induction", "mec-fringing-derate") with full input traceability.
• Schema: calcMotorSchema.required reduced to ["pole_pairs", "turns_per_phase"]; mode-specific inputs validated at runtime.
• Tests: Comprehensive coverage in ecad.test.ts including reference machine validation (N=30, kw=0.866, p=3, I=1.5 A, f=100 Hz → B1 ≈ 4.7 mT, locked-rotor ≈ 18 µN·m), scaling laws, and edge cases.

Files Modified

• packages/mcp/src/tools/ecad.ts — calcMotor() refactored to dispatch on mode; new `calc

https://claude.ai/code/session_01J1BhGkMGF3m4hEDXVKeTar

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Project	Deployment	Actions	Updated (UTC)
vcad-mcp	Ready	Preview, Comment	Jul 7, 2026 2:24pm

3 Skipped Deployments

Project	Deployment	Actions	Updated (UTC)
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vcad-docs	Ignored		Jul 7, 2026 2:24pm

[chojiai]

What shipped

The motor analysis tools now support two new capabilities alongside the existing permanent-magnet mode.

• Induction motor sizing: calc_motor gains an induction mode for drag-cup and PCB-rotor designs, computing the rotating air-gap field, torque per unit slip, locked-rotor torque, synchronous speed, and rotor heat dissipation from the rotor sheet's conductivity and geometry.
• Fringing derate for PM flux: When you supply the magnet pole width, the PM flux prediction is automatically corrected for pole-edge fringing, and both the raw and derated values are reported so you can see the adjustment.
• Self-start check: A new check_self_start tool answers whether a motor will overcome bearing friction at standstill, returning a pass/fail verdict against worst-case friction (from a built-in bearing catalog or a number you supply directly), a best-case verdict, and a safety margin.

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_{Plain-English summary generated by Choji from this pull request.}