← Robot list · Singularities course
Turn the robot with the mouse or your finger. Click an axis (a coloured circle or a card) to light up its ring and its axis and to read its description, press X-ray to look inside at the motors, gearboxes, controller and cables, and move each joint with its slider.
Six numbers place the platform in space; the six legs follow.
The fixed frame, bolted to the floor. It carries the six actuators.
Six legs whose length changes, each driven by a motor and a ball screw (electric) or by oil (hydraulic). Changing the six lengths moves the platform in all 6 degrees of freedom.
Each leg is held at the base by a universal joint (2 rotations), so that it can tilt in any direction.
At the top each leg ends in a spherical joint (3 rotations). The legs come in pairs that share neighbouring points.
It carries the load. Its pose has 6 numbers: x, y, z, roll, pitch, yaw. It is very rigid because the six legs share the load.
A flight-simulator cabin, a telescope mirror, a machine tool or a surgical tool: the Stewart platform moves heavy loads with high precision.
The six leg lengths are computed live from the pose of the platform (inverse kinematics: one simple formula per leg, the distance between the base joint and the platform joint). A leg turns red when it leaves its stroke (550 to 950 mm here) and the pose is then not reachable. Angles are roll (about the forward axis), pitch and yaw. The model is simplified: the real inside depends on the make. Stewart platforms also have singular poses (see lesson 8 of the course on singularities).