When making robots we often purchase servo motors, but the enjoyment of assembling themselves, including those parts printed by 3D printing, is exceptional.
Plastic gears and bearings, small motors can be found on eBay. In order to simplify the mechanism, 2mm screw shaft and a nuts were combined to make a linear type servo motion.
The positioning mechanism consists of a Hall sensor and small magnets. Sensor detects the position by counting the rotation of the shaft.
The control circuit of each servo consists of ATtiny44/84, H-bridge motor driver and Hall sensors. The control board of the main unit controls 4 servo mechanisms from ATmega328P.
It has 4 light sensors and an IR receiver and detect hand gesture and IR remote controller signals.