Window shade and actuating system thereof

An actuating system for a window shade, comprising:

• a transmission axle having a longitudinal axis and rotationally coupled to an axle adapter, the transmission axle and the axle adapter being rotatable about the longitudinal axis;
• a brake assembly including an arrester, a rotary element rotatable about the longitudinal axis, and a shift collar configured to couple the rotary element to the arrester and decouple the rotary element from the arrester, the shift collar switching from a decoupling position to a coupling position in response to a rotation of the rotary element in a first direction and from the coupling position to the decoupling position in response to a rotation of the rotary element in a second direction opposite to the first direction;
• and
• a clutch configured to couple and decouple the axle adapter from the rotary element, the clutch having a clutch actuator rotatable about the longitudinal axis, the clutch actuator being operable to switch the clutch between a clutch coupling state and a clutch decoupling state.