A holder assembly (2) comprises a motor and a first shaft arm (3). The motor drives the first shaft arm (3) to rotate. The holder assembly also comprises a limit member. The limit member is connected between the motor and the first shaft arm (3). The limit member and the first shaft arm (3) can rotate within a first preset angle range, and the limit member and the motor can rotate within a second preset angle range. According to the invention, the limit member and the first shaft arm can rotate within the first preset angle range, the limit member and the motor can rotate within the second preset angle range, and rotating angles between the first shaft arm and the motor can be limited, thereby preventing electric wires connected between the first shaft arm and the motor from intertwining with each other and even breaking because the rotating angle of a holder is too wide.