A spinning blade propulsion system used in air and water travel. The blades are angled so they push the medium(that is the air or water - both refered to also as fluids in this context) in a direction continuously.
Helicopters use a very specialised propellor in which each individual blade can be rotated and positioned as they rotate. They take their name from the fact that the force in a Propellor or rotor is Helical - that is spiral like.
Time to build your own robot! Using a Raspberry Pi with parts and some time, you can use my book to learn how to make and program a robot with automatic behaviours.