Dynamics of Aircoast drone
Drones are normally being propelled by four propellers (affectionally called quadcopter) although it could have more like six or eight. The shape of the propeller is designed to propell air from above the propeller to the bottom, causing the air behind the propeller to give an upward trust to the craft.
When trust power is increased, the drone will fly upwards due to the greater force under the propellers and when the trust is reduced, the drone will fall back to earth due to greater gravity force acting on the drone craft.
You will notice that adjoining propellers spin contra to each other. There is a reason for this. If all the propellers spin in the same direction, then the craft will have an additional motion like rotating on its axis. This also apply to a helicopter which normally has only one main rotor. A helicopter has an additional tail rotor to counter this spinning on its axis effect. This we do not want and in order that the craft is prevented on spinning along its axis, adjoing propellers are made to spin contra to each other. So when yoy assemble a quadcopter (or any other type), you have to ensure that the propellers spin contra to each other like in the diagram above.