Build a simple pendulum, a pulley system, or a lever system to study the motion and forces of different mechanisms.
Design a mechanism to control the speed of a motor, a gear train, a differential gear, or a spring-powered device.
Construct a robotic arm, a hexapod, a biped walking robot, or an animatronics hand using Arduino or other microcontrollers.
Create a windmill, a solar tracker, or a hybrid vehicle to generate and use renewable energy.
Fabricate a material using a 3D printer or a CNC machine.