Four sizes of the same printed axial-flux design (only Do changes) mapped onto a 30 kg humanoid. The budget delivers the thread's blunt finding: a full 25-DoF fully-printed bonded-magnet humanoid does not close — 18 kg of actuators is 60% of a 30 kg robot. It closes as a lean 14-DoF walker at 34%, and comfortably as a sintered-leg hybrid at 25%. The sovereignty tax is now a number.
| size | OD | peak | cont* | Kₘ | module |
|---|---|---|---|---|---|
| XS | 75 | 28 | 14 | 0.49 | 0.54 |
| S | 90 | 49 | 24 | 0.71 | 0.77 |
| M | 110 | 89 | 44 | 1.06 | 1.16 |
| L | 130 | 146 | 73 | 1.48 | 1.62 |
Real humanoids run 30–50% of mass in actuation. Config A blows past it because low-torque-density printed bonded magnets multiplied across 25 joints simply weigh too much — every joint is correctly sized (all margins > 1.0), the count × mass is what fails. Cutting to a 14-DoF walker and letting the legs use sintered magnets both bring it home.
| Joint | × | DoF/side | req peak | size | peak | margin | mass |
|---|---|---|---|---|---|---|---|
| LEGS | |||||||
| Hip (pitch + roll) | 2 | 2 | 45 | S · 90 | 49 | ×1.08 | 1.55 |
| Knee | 2 | 1 | 55 | M · 110 | 89 | ×1.61 | 2.31 |
| Ankle (pitch) | 2 | 1 | 40 | S · 90 | 49 | ×1.21 | 1.55 |
| ARMS | |||||||
| Shoulder (pitch + roll) | 2 | 2 | 25 | XS · 75 | 28 | ×1.12 | 1.08 |
| Elbow | 2 | 1 | 18 | XS · 75 | 28 | ×1.56 | 1.08 |
| HANDS → tendon-driven (LEAP / ORCA class), outside the AXF-1 family | |||||||
| TOTAL | — | 14 DoF | — | — | — | — | 10.2 kg |
Torque targets are design intent for a squat-capable walker with mild dynamic margin (~1.5–2 N·m per kg of robot on the demanding leg joints). Knees are the one joint forced to M — the D³ torque wall. Hands are a separate problem (tendon drive), already flagged in the capability map.
25 → 14 DoF drops actuators from 18.0 to 10.2 kg. Dropping hip-yaw, ankle-roll, shoulder-yaw and wrists (to tendons) costs some dexterity and turning grace but is the difference between infeasible and buildable. The Berkeley-Lite lesson: minimal DoF is a printability strategy, not a compromise.
Let the leg joints (knees, hips, ankles) use sintered NdFeB — ~2× torque density → ~0.6× module mass — while arms stay fully printed. Total falls to 7.4 kg / 25%. The full-print sovereignty tax is +38% actuator mass. A clean, quantified choice: pay 38% for rare-earth-independent, fully-printable legs, or don't.
Torque ∝ D³, and mass ∝ D², so a joint spec'd for backflips instead of walking jumps a size and gains ~50% mass. Size honestly to the gait. Every unnecessary N·m of peak is paid for in kilograms across 14–25 joints.
Raising the robot to 40 kg lowers the fraction, but required joint torque scales with mass × length, so the actuators grow too — it mostly chases its own tail. Better to attack the numerator (DoF, magnets) than inflate the denominator.
A 14-DoF, 30 kg biped: knees on M (110 mm), hips/ankles/shoulders on S–XS, hands on tendon. 10.2 kg of fully-printed actuators — 34%, inside the humanoid norm — with a drop-in path to 25% the day you allow sintered legs. This is the honest envelope of a fully-printed bonded-magnet humanoid: lean it, or hybridize it. A dexterous 25-DoF fully-printed machine at this scale waits on either a print-native higher-flux magnet or the SRM / rare-earth-free variant — which is exactly why that branch stays alive in the build order.
Nothing here moves until MEAS-1: the whole family's torque column rides on printed-magnet Br. Measure the coupon, then this table is real instead of intended.