Twist adds up to zero

Canceling out to zero

Now look at the twist on the body. The two blue arrows twist it clockwise, and the two orange arrows twist it counterclockwise. When all four propellers spin at the same speed, the two sides are equal and cancel out. So the big arrow in the middle disappears, and the body does not spin.

Why?In a tug-of-war, if both teams pull equally hard, the rope does not move. The clockwise pair and the counterclockwise pair twist the body equally hard in opposite directions, so the total is zero. Unlike a helicopter, a drone needs no tail rotor.

Go furtherThis balance is the key to turning on the spot, coming up later. Spin one pair harder on purpose, and the balance breaks, so the body turns.