Production hardware | DFM and integration

Zerith Humanoid Production Hardware

Mechanical design for humanoid production at 200 units/month, including 3-axis CNC motor mounts, six-axis wrist force sensing, and a thin 3-DOF neck.

Mechanical Engineering Intern | Zerith Robotics | Shenzhen, China | Jul 2025 - Nov 2025

Multiple Zerith H1 robots undergoing development and testing in an engineering lab — Zerith H1 engineering and test environment

Production hardware

Summary

200

Units/month

5-axis to 3-axis

Motor mount machining

6-axis

Wrist force sensor

3-DOF

Thin neck mechanism

Each design had to support repeatable machining, assembly, and packaging at 200 units/month.

Production requirements

Designing for production volume

At 200 units/month, each mechanism needed a repeatable machining and assembly route suitable for production. I applied those requirements to motor mounts, a wrist force-sensor interface, and a thin neck mechanism.

Responsibilities

My role

I designed motor mounts, revised the wrist interface, and developed linkage CAD and engineering drawings. I converted packaging and mechanism requirements into manufacturable parts, then documented the interfaces for engineering review and production.

Machining redesign

Motor mount redesign

Replacing a 5-axis undercut with standard 3-axis CNC

The original motor-mount geometry included undercut features that required 5-axis machining. I removed those features while preserving the interface and load path needed by the mount.

Reworked the mount profiles so the required faces could be reached with standard 3-axis CNC tool access.
Converted a specialized 5-axis machining requirement into a conventional 3-axis CNC process.
Broadened the available supplier pool and simplified sourcing for the required production volume.
Evaluated the DFM changes against the full assembly interfaces and the standalone part geometry.

CAD model of a revised orange motor mount with machined tool access — **Revised mount geometry** CAD study removing the undercut features that drove the original 5-axis process.

Manufactured aluminum motor mount on a workbench — **Manufactured bracket** Physical part produced from the revised geometry.

Wheel motor installed in the manufactured aluminum motor mount — **Assembly fit check** Wheel motor mounted against the final bracket interfaces.

Tolerance stack

Wrist force-sensor integration

Six-axis wrist sensing

I integrated a six-axis wrist force sensor to enable force-touch sensing. When assemblies failed to fit, I traced the problem to a tolerance stack across the mating interfaces rather than a single defective component.

Mapped the interface stack to identify which dimensions drove fit sensitivity.
Redesigned the interface geometry to reduce sensitivity to accumulated variation.
Updated GD&T to communicate the revised datum and tolerance intent.
Documented the integration change for engineering review.

Physical six-axis wrist force sensor with its mounting flange, electronics, cable, and mating hardware visible on the assembly bench — **Six-axis force sensor** Physical sensor used at the humanoid wrist interface.

Annotated CAD view highlighting the overconstrained wrist force-sensor interface — **Fit failure diagnosis** Annotated interface showing the X and Y locating surfaces that overconstrained assembly.

Revised wrist force-sensor interface CAD model with the updated locating surface — **Revised interface** The revised locating surface left room for manufacturing variation.

Dimensioned CAD study of the revised wrist force-sensor interface — **Dimension study** Dimensioned interface record used to communicate the revised datum strategy.

Mechanism design

Thin 3-DOF neck

3-DOF motion in a thin package

I collaborated with a senior engineer to develop a thin 3-DOF neck mechanism for a humanoid robot. The visible neck had to remain compact and human-proportional while the linkage provided pitch, yaw, and roll.

Developed linkage geometry and iterated the mechanism CAD around the packaging envelope.
Checked clearances and interfaces across the complete assembly.
Prepared engineering drawings that captured the mechanism interfaces for engineering review.
The resulting drawings supported a patent filing.

Exploded CAD view of the Zerith humanoid robot 3-DOF neck linkage and actuator assembly — **Neck linkage record** Exploded assembly view showing the compact pitch, yaw, and roll mechanism.

Exploded engineering drawing of the Zerith humanoid robot neck assembly — **Assembly drawing** Engineering record for the head, linkage, and mounting interfaces.

Zerith H1 upper-body close-up showing the head, shoulders, and compact neck region — **Robot package** Reference view of the robot package the mechanism had to fit.

Design records

Tools and design documentation

SolidWorks Siemens NX GD&T 3-axis CNC Tolerance analysis Engineering drawings

The design records cover the motor-mount tool-access change, the wrist-interface tolerance chain, and a kinematic diagram of the 3-DOF neck.

Dimensioned engineering drawing of the Zerith humanoid robot motor mount — **Production drawing** Dimensioned motor-mount record used for machining and inspection.

Dimensioned drawing of the revised wrist force-sensor interface — **Datum and tolerance study** Interface dimensions used to review fit sensitivity.

Exploded kinematic drawing of the Zerith humanoid robot neck mechanism — **Kinematic assembly** Linkage and actuator arrangement for the thin 3-DOF neck.