CC0 · public domain MEAS-1/ printed-magnet remanence protocol/ the gate before RFQ

MEAS-1 — does the printed magnet hold Br?

Every torque number in the AXF-1 family is proportional to magnet remanence B_r, assumed at 0.62 T. This protocol prints the magnet on the production process, magnetizes it, and measures B_r — at operating temperature, not just at 25 °C — then converts the reading into a verdict on the family. Nothing goes to a metal-AM bureau until this coupon is measured.

PASS / FAIL

What the number decides

evaluate at hot, T_op = 100 °C

The derate rule — torque scales linearly with hot remanence

T_actual = T_family × ( B_r,hot ⁄ 0.62 )
B_r,hot = B_r,25 × [ 1 − 0.0011 · (T_op − 25) ] NdFeB reversible coeff ≈ −0.11 %/°C → ×0.92 at 100 °C, ×0.90 at 120 °C

B_r,25 ≥ 0.64 T	Family holds hot, as drawn. Hips clear their peak with margin at 100 °C. This is the top of the isotropic-bonded window — likely needs aligned (anisotropic) powder to reach.
0.57 – 0.64 T	Holds cold; hip-pitch marginal-to-under HOT. Upsize hip-pitch S → M, or cap winding temperature / duty so the joint never runs at its hot floor.
0.50 – 0.57 T	~10–20 % haircut across the board. Resize hips (verify knees still clear at M), or cut the robot's mass / torque target. The family survives, resized.
< 0.50 T	Isotropic bonded is insufficient. Move to anisotropic (field-aligned) bonded, or sintered-magnet legs — the hybrid path (+38 % actuator mass, already quantified).

Canary joint = hip-pitch (size S, margin ×1.08) — the first to fail as B_r drops. Then ankle-pitch (S, ×1.21, hot floor 0.51 T). Knees (M, ×1.61) stay safe down to ~0.42 T. At exactly B_r,25 = 0.62 T the hot hip-pitch peak lands at 45.0 N·m = its requirement — no margin. So even the design value is a knife-edge hot: expect this measurement to push a hip upsize or a hybrid, and treat that as information, not failure.

WHY HOT

Remanence, the knee, and the operating point

second-quadrant demagnetization

Fig.4 — B_r is where the curve meets the B-axis (H = 0). Heating does two bad things at once: it lowers B_r (white → red curve) and moves the knee toward the operating load line. Keep the operating point B_d above the hot knee, or the magnet takes irreversible loss. The hot curve here starts below the hip floor — passes cold, fails hot. That is the failure mode MEAS-1 exists to catch.

COUPONS

What to print

production process, unchanged

Coupon	Geometry	Purpose / rule
B_r cylinder	Ø12.5 × 12.5 mm	Regular geometry with flat parallel faces for the permeameter fixture (L/D ≈ 1 minimizes demag correction). Same printer, material, layer height, and parameters as the production magnet.
B_r cube (alt)	10 × 10 × 10 mm	Alternative for Helmholtz-coil moment measurement, which is geometry-tolerant.
orientation set	×2 print axes	Print the flux axis parallel and perpendicular to the build layers — FFF bonded can be mildly anisotropic from bead/layer structure. Measure both; design to the weaker.
density coupon	≥ 10 × 10 × 10 mm	Archimedes density → packing fraction φ, the causal variable behind B_r. Correlate: if B_r is low because φ is low, chase print parameters; if φ is high and B_r still low, the powder is the ceiling.
count	N ≥ 5 each	AM has batch spread. Report mean ± σ; pass on mean − 1σ clearing the floor, not the best coupon.

PROCEDURE

Print → saturate → measure → heat

Density & packing fraction

Archimedes weigh each density coupon. φ = ρ_coupon / 7500 (NdFeB solid density). Record before magnetizing — it explains the B_r you get.

Magnetize to saturation

Pulse magnetizer with a fixture coil, applied field ≥ 3 T (≥ 3–5× H_cj). Verify saturation: measure, re-magnetize at higher field, re-measure — if B_r does not rise, it is saturated. Under-magnetization is the most common false-low.

Measure B_r at 25 °C

By one of the three tiers below. Helmholtz moment gives B_r = μ₀ · m / V directly (m = measured moment, V = coupon volume). Hysteresisgraph gives the full loop — B_r, H_cb, H_cj, and the knee.

Measure or compute hot B_r

Heat-soak to the winding operating temperature (100–120 °C) and re-measure, or apply the −0.11 %/°C coefficient and confirm with at least one hot point. The hot value is what the derate rule uses — the design must pass hot.

Irreversible-loss check

Measure B_r at RT → heat-soak at T_op under the expected open-circuit / demag load → cool → re-measure at RT. Any permanent drop means the operating point fell below the hot knee: the magnet partially demagnetized in service. Derate or change material — this is a safety gate, not a data point.

Hysteresisgraph

reference · lab equipment

Best.

Closed-loop permeameter + fluxmeter. Full second-quadrant loop: B_r, coercivities, and the knee (needed for step 5). Per ASTM A977 / IEC 60404-5. Use a partner magnetics lab if you lack one.

Helmholtz + fluxmeter

accessible · buildable

Recommended for the lab.

Helmholtz coil pair + integrating fluxmeter reads total moment → B_r absolute, geometry-tolerant. Gives B_r (not the full loop). Cheap to build; standard QC method.

Hall probe + model

screen · cheapest

Calibrated gaussmeter on the standard cylinder at a fixed on-axis point, back out B_r analytically or by FEA. A $100 quick screen for relative batches — not the absolute number of record.

Expected outcome — read this before you print. Isotropic MQP powder tops out near 0.8 T at full density, so B_r ≈ φ × 0.8 before print porosity even enters. FFF bonded typically lands at φ ≈ 0.55–0.70 → B_r ≈ 0.44–0.56 T — squarely in the "resize hips or hybridize" band, below the 0.574 T hot floor. The family's 0.62 T is optimistic for isotropic FFF. The most likely MEAS-1 result is not "pass" — it is a quantified instruction to upsize hip-pitch, move to aligned powder, or run sintered legs. That is the protocol earning its place: it turns a hopeful spec into a decided one.

REF

Reference standards

ASTM A977 / A977M	Hysteresigraph measurement of permanent-magnet DC properties — the reference loop method.
IEC 60404-5	Magnetic materials — permanent (hard) magnetic materials, DC magnetic properties.
Helmholtz-coil moment method	Total magnetic moment → open-circuit B_r (IEC 60404-14 / common practice). The accessible tier.
ASTM B962	Archimedes density of powder-metallurgy parts — packing fraction φ (step 1).

Confirm current editions before citing in a report; titles/scopes summarized here.