What does the top of a toy helicopter do?

It is common sense that when the main propeller of a helicopter rotates at high speed, it will give the fuselage a reaction force and make the fuselage rotate in the opposite direction. So a helicopter can't fly without a fixed tail. The model helicopter uses the tail rudder to change the angle of attack of the tail rotor, and then changes the thrust of the tail rotor to balance the reaction force brought by the main rotor to keep the fuselage from turning. Generally, gyroscope is an accelerometer, which is used to feel the deviation of helicopter tail. If the remote controller doesn't give instructions, such as windy, if the tail direction is deviated, the gyroscope will feel the deviation and automatically give instructions to the tail steering gear to correct the tail direction to ensure that the fuselage always faces in one direction. This kind of gyroscope is usually called tail-locked gyroscope. Higher-end gyroscopes, with two or even three accelerometers built in, can not only feel the tail deviation, but also feel the roll and pitch channels of the fuselage, so that the helicopter fuselage can automatically maintain its current height without receiving remote control signals, and hover stably without running around.