Khosrobot lab
The Khosrobot rig running in your browser. Pick a part and pull it, turn it, or stretch an arm.
This rig is a mixture of two techniques, and both are used here: geometry-based rigging and physics-based rigging. Neither alone gives this behaviour. Geometry makes a mechanical character precise and fast; physics makes it react.
01 The ideas
Geometry places the parts
Mechanical parts are placed by equations, not by simulation: the wheel rolls on its surface and never enters it (Newton-Raphson), the elbow hinges and telescoping arms come from 3D geometry, and linear algebra drives the crown, the eyes and the hands.
Physics moves the body
The body, arms, elbows, hands and the hand doors are rigid bodies joined by constraints, so a drag pushes the rest of the character around and it settles again. This is the idea of Physirig, here as a light web version.
The two run in order
Each frame, the physics pass runs first (drag, joints, collisions). The geometry pass then reads its result and places everything else: the wheel, the arms’ reach, the head, the eyes and the doors.
02 Geometry-based rigging
A precise and fast kind of rigging, fairly hard to implement, made for an AR project. It suits mechanical rigs best, since they are built from pseudo-primitive shapes. Because such rigs are low-level and fast, they export easily to game engines and run well on mobile platforms, which is why they also run in a web page. The full story is on the Geometry-based rigging page.
03 Physics-based rigging
Physirig adds collisions, physical constraints and physics-based posing to a rig. After building several geometry-based rigs, this was the natural next step: the parts of the character can push and pull each other. The original runs on Nvidia PhysX inside Blender. This page uses a light web version on Rapier, with simple shapes as colliders; it is not the full Physirig. See Physirig.
04 Things to try
The Help panel on the right lists the controls. Drag an arm and watch the body follow; press G to grab without holding a button; press R once for a turn around the view and twice for a trackball; select an arm and press S to lengthen it. The Controls panel on the left opens and closes the doors and the eyelids.