Physical Ash: measure before building

October 12 approval: paper design only

At 14:55 UTC on October 12, the owner approved the documented paper-design direction: a stationary serviceable chassis, fixed compute and camera, and a removable low-mass motion module. This approves the direction for further paper design; it does not approve unknown detailed choices.

At 14:56 UTC the owner reaffirmed the hardware hold: no hardware changes until the hardware is correct, approved and tested on paper. No hardware changes or powered testing are authorized by this approval. Exact sizing, part and driver compatibility, power, protection and safety decisions remain open. G0–G7 remain OPEN / NOT RUN.

The original proposal below is retained as the pre-approval planning record. Its detailed dimensions, component selections and test activities remain provisional. Publishing this note does not supply physical test evidence or alter the installed system, animation or character canon.

Original proposal history, not built or tested

The next physical Ash prototype should begin with a stationary, serviceable bench chassis. Keep the compute stack and camera fixed, then investigate one small expressive motion in a separate lightweight module. Measure the assembled hardware before designing the enclosure.

This is a recommendation for review. Publishing the plan does not adopt the architecture, approve construction, release a powered test, change the installed system or alter Ash’s approved character appearance. No new physical hardware tests were performed for this article. All gates G0 through G7 below remain OPEN; their planned activities are NOT RUN.

A chassis that can be inspected and repaired

Start with a low, stable base and removable modules for compute, power distribution and any future motion. Board loads should pass through verified mounting points and standoffs. Connectors, ribbon latches, the cooler and the circuit boards themselves must not become structural supports.

Survey the installed Pi, cooler and accelerator stack as one assembly. Its working bench configuration does not establish clearance or cooling inside a new body. An open prototype makes these checks easier, even though it looks less finished.

The base needs a reviewed load path and stability margin for every proposed pose and cable pull. A center of gravity inside the footprint is only a static starting point; it does not prove stability during movement. Materials, thickness, fasteners and allowed deflection remain to be selected from measured loads.

Measure geometry before drawing the shell

Choose a repeatable base plane and forward, left and up directions. Record installed width, depth and height, mounting-hole locations, underside projections and cable exits. Measure the space needed to insert and remove each plug, release each latch and reach each fastener.

The design envelope must include manufacturing tolerance, electrical clearance, cooling space and service access. Nominal board dimensions leave out plugs, wires, tools and the route needed to remove a module.

Use a separate mockup when measurement would disturb the qualified stack. The proposed survey must not become an unplanned unplugging, lifting or disassembly session. A shell should follow the measured engineering envelope and approved character references.

Keep the moving module light

Evaluate one owner-selected expressive feature or head subassembly first. Reduce moving mass and keep its center of mass close to the axis before considering a larger actuator. Whole-body movement is deferred.

A bearing or guided support may be needed to carry bending and side loads; a servo output spline is not automatically a suitable structural bearing. Review retention, loosening, backlash and the removable interface.

No axis count, servo assignment, linkage ratio, angular range or speed is selected by this plan. Mechanical restraint must address what happens if power is removed from a gravity-loaded joint.

Preserve camera coverage and service access

The camera should begin on a fixed bracket that can be adjusted and then locked, outside the moving load path. Verify its actual configured view at the intended height and user distances, including seated and standing coverage, focus, edges and any obstruction from the shell.

Keep ribbon strain away from latches and leave microphone and speaker placement flexible until the actual devices and acoustic route are qualified. Camera coverage and quiet audio cannot be assumed from a rendering.

A removable cosmetic cover should carry no structural load, conceal no disconnect and leave ventilation accessible. Keep loose fibers clear of fans, hot surfaces and joints. Review pinch and snag locations, rounded edges, guards, connector labels and the service sequence.

Servo identity is clearer; compatibility remains open

Packaging evidence corroborates Hiwonder HPS-0127 PWM servo, MPN 21100204. It does not establish the contents or condition of each unit, the servo-body revision, connector details, usable torque or electrical compatibility.

The manufacturer page lists 7.4–8.4 V, but its tables conflict: maximum torque is stated as 1.5 versus 1.8 kgf·cm, and travel as 270 versus 280 degrees. These are unresolved catalog claims, not validated ratings or selected RC-01 operating values. The manufacturer link is provided below.

No power until review: confirm the exact servo units and revisions, authoritative documentation, driver-board circuit and power path, logic compatibility, supply and protection before any powered servo test. Torque, current and travel inputs stay unknown until reconciled. A clutch or stall claim does not prove safe continuous operation or pinch protection. This article supplies no wiring recipe.

Budget the load at each joint

For the worst proposed pose, calculate the gravity torque of every downstream mass: torque in N·m = sum of mass in kg × 9.80665 m/s² × perpendicular moment arm in m. The moment arm is the distance that lets the load turn the joint.

Add the torque needed for acceleration, friction and cable resistance. Apply a reviewed design margin and account for any transmission ratio and efficiency before comparing with verified usable actuator torque at the actual supply and duty cycle. Track speed and bearing/fastener loads separately.

A balanced vertical rotation axis may have little gravity torque but still needs acceleration and cable torque. Stall torque and no-load speed are not continuous-load qualifications. For unit consistency, 1 kgf·cm = 0.0980665 N·m; the NIST reference is linked below.

Power and cables need measured budgets

Build a budget for each actual voltage rail under idle, perception, speech/audio, motion and permitted simultaneous operation. Power = voltage × current. Average demand helps estimate energy use; peak demand and its duration determine whether the supply, regulator, connector and conductor can deliver a transient.

Add power across different-voltage rails rather than adding their currents. Include conversion losses, and avoid counting the same downstream loads both inside a Pi input measurement and as separate loads. Average current does not replace RMS current when estimating resistive heating.

Before topology or parts are selected, review the exact driver board, supply and return paths, compatibility and potential back-feeding. Do not assume a Pi rail can supply servos or that separate supplies can be joined. The layout is a design question, not an approved connection.

For a measured complete cable loop, voltage drop = peak current × loop resistance; resistive heating = RMS current squared × loop resistance. Include connectors and returns. Record lengths, flex and bend limits, service slack and the whole motion path. Route away from rubbing, sharp edges, pinch points and fan blades. CSI and PCIe ribbons are different interfaces.

Cooling must be tested in the proposed enclosure

Keep chip telemetry, measured component surfaces and accessible shell temperatures separate. Record ambient temperature and a defined workload, then compare the open chassis with the later shell under equivalent conditions.

Track temperature rise, hot spots, fan state, health flags and time to a reviewed steady-state criterion. Limits must come from applicable component and material ratings and intended touch exposure, with reviewed margins.

Historical healthy Pi readings do not qualify a new enclosure or a safe touch temperature. Airflow and heat paths change with packaging; estimates need measurement. Extra fans, ducts or sound treatment should be justified by temperature and microphone-noise results. No blocked-fan or unattended overload test is proposed.

Eight gates before a physical release

Every gate below is OPEN. Activities are planned and NOT RUN; no numerical acceptance limits have been silently filled in. Advance only after the required review, specific authorization and retained evidence.

The next handoff is measurements

Begin with an authorized, unpowered identity and geometry survey: actual part labels and revisions, installed stack and plug envelopes, mounting points, cooler airflow, bench footprint, support points, user approach and cable entry directions.

Define the intended moving feature and pose range, then measure each moving mass, its center-of-mass distance from the axis, the support arrangement and proposed motion purpose. Record camera position and intended viewing distances, cable identities, lengths and available slack. Use a separate mockup if the live stack cannot be surveyed safely.

Electrical and thermal/acoustic measurements belong to separately approved powered test plans. Record units, instrument, date, conditions, revision, uncertainty and evidence for each value. Unknowns remain blank rather than being treated as zero.

Synthetic calculation or workbook checks verify the arithmetic and missing-input handling only. They do not qualify physical servos, power delivery, temperature, fit, stability or motion. The next result should be a measured envelope and reviewed candidate budgets, not a shopping list or a declared finished robot.

Keep the test boundaries explicit

A later test must stop for unexpected movement, tipping, loose retention, cable strain, smoke or odor, abnormal heat, supply collapse/reset, a limit crossing or uncertain part identity. The reviewed energy-isolation method must account for a load that could fall when power is removed; preserve the observation and investigate before retrying.

No intentional stall, finger-pinch, short circuit, blocked ventilation, unattended endurance or destructive fault test is included in this proposal. Perception or conversation software is not an independent safety function.

The current voice, hardware and animation acceptance gaps remain separate. Neither this article nor its publication closes those gates or approves an everyday configuration.