From CAD to Humanoid: Designing, 3D Printing and Bringing to Life Humanoid Robots — Mechanisms, Muscles, Skin, Faces and Senses, with the Science Behind Them

From CAD to Humanoid is a hands-on guide for makers, engineering students, roboticists and designers who want to build humanoid robots with today's desktop tools. Enclosed printers turn carbon-fibre nylon into load-bearing joints overnight, affordable brushless motors give them real torque, and free CAD software holds the whole design together. The same printer that makes a knee bracket also makes the mould for a silicone face, the skull beneath it and the eyeball that looks out of it. This book teaches that design–print–test loop from end to end.

One running example ties everything together. PRIMA is an open humanoid about 1.0 m tall with 23 actuated joints driven by printed planetary and cycloidal quasi-direct-drive actuators. PRIMA-S is its 40 cm serial-bus-servo starter sibling. PRIMA's lifelike modules add an expressive silicone-skinned face on a printed skull, with camera eyes, eyelids, a moving mouth and rooted hair, and a tendon-driven hand with tactile fingertips. You design, print, test and simulate them chapter by chapter.

Current to October 2026, with more than 250 listings run while the book was written: build123d and CadQuery parts, FreeCAD and OpenSCAD scripts, FEM checks, OrcaSlicer runs, URDF and MJCF robot models and Python calculations for torques, gears, bolt loads, cure times and sensor circuits.

What you will learn

The CAD tools, in depth: FreeCAD 1.1 (Sketcher, Part Design, Assembly, FEM with CalculiX, Python), Onshape (variables, configurations, mates, FeatureScript, onshape-to-robot), build123d code CAD and OrcaSlicer, plus Fusion, CadQuery, OpenSCAD, Blender face sculpting, topology optimisation and AI text-to-3D generators such as Meshy, including how to give them dimension specifications.

Design for 3D printing and casting: engineering filaments, anisotropy and layer strength, tolerances and fits, heat-set inserts and bolted joints, snap fits and printed mechanisms, slicer settings for strong parts, hybrid carbon-tube links, and printed moulds for silicone.

Actuators and the mechanical body: torque and mass budgets, printed planetary, cycloidal and strain-wave gearboxes, quasi-direct-drive actuators and field-oriented control, hips, knees, parallel ankles, feet with load cells, torso, arms, hands and wiring.

Lifelike humanoids: McKibben, hydraulic, twisted-nylon and electroactive artificial muscles, biomimetic movement and reflexes, silicone skin and its colouring, tactile skins, faces with twenty actuators and the Facial Action Coding System, camera eyes with saccades and blinks, hair rooting, mouths, lip-synced speech, hearing and an electronic nose.

From CAD to simulation: mass properties and inertia from CAD, URDF from build123d, MJCF, SDFormat and USD, and design verification in MuJoCo that changes the robot: torque checks, drop tests and self-collision sweeps.

Building and testing: bills of materials, print planning for a print farm, test rigs and fatigue, costs from prototype to moulded parts, and a survey of open-source humanoids and their licences.

The science beneath the machine: self-contained deep dives into the mathematics (rotations, kinematics, NURBS, optimisation), physics (dynamics, balance, elasticity, fatigue, fluids, heat, sound and light), electrical engineering, sensors and control, chemistry (polymers, silicones, adhesives, batteries) and biology (muscles, skin, senses, nerves and the face).

Every practical chapter carries short "The science behind it" boxes with one mechanism, one formula and one worked number, each pointing to its full treatment in the final part. Read straight through and you build a robot; follow the pointers and you learn why it works. Results from simulations and calculations are labelled as such, and product claims are marked as claims.