MG90S Six-Servo Stewart Platform

This is a desktop Stewart platform, also called a hexapod motion base. Six MG90S micro servos swing short crank arms, and each crank pushes a rigid rod with a print-in-place ball joint at each end. Together the rods move a 130 mm top platform in all six degrees of freedom: X, Y and Z translation plus roll, pitch and yaw. It's aimed at hobbyists who want a working small camera stabiliser, flight-sim cockpit demo or inverse-kinematics testbed. The ball joints are usually where these builds stall, and here they come already printed, with no RC ball links to hand-fit. A Pi Zero (or any controller) and a PCA9685-style servo driver mount on the electronics deck under the base, and that deck's three legs also serve as the feet.

The base is a lightened 170 mm plate. Six servo cradles bolt to it in three pairs, each held by two M3 screws into heat-set inserts. Every cradle holds a servo horizontally with its shaft pointing radially outward. A crank arm screws onto each servo's stock single-arm horn through a slot, so it fits whatever horn your servos came with. Each pushrod bolts to its crank tip with an M3 screw and nylock nut, and its other end bolts to the underside of the top platform. The joint pairs on the platform are rotated 60° from the servo pairs on the base, which is the classic Stewart layout.

Assembly order:

1. Press M3 heat-set inserts into the base's 12 cradle holes and into the tops of the electronics deck's 3 legs.
2. Screw the electronics deck under the base with 3x M3x10. Mount the Pi Zero and servo driver on the deck.
3. Bolt the six servo cradles to the base with M3x10 screws, then slide each MG90S in from the inboard side and fix it with its tab screws.
4. Power the servos to 90° (centre). Fit the stock single-arm horns pointing horizontally and screw a crank arm onto each horn through its slot.
5. Break each pushrod's ball joints free by flexing them gently. Bolt the lower stud of each rod to a crank tip with M3x16 and a nylock nut.
6. Lower the top platform onto the six upper studs and bolt them with M3x16 and nylocks. Leave every nylock just short of tight so the stud tabs stay square without binding.

Tuning notes: calibrate each servo's centre offset in software before running IK. At neutral the platform sits about 95 mm above the base top. Sizes in the IK model: crank radius 24 mm, rod length 100 mm between ball centres, base joint circle about 62 mm, platform joint circle 50 mm. Keep crank travel within ±60° so the ball-joint cones don't bottom out. Use a separate 5 V supply rated 5 A or more for the servos; do not power them from the Pi.