in the DX7 is the upper-right switch of the Tx (it says HOLD I think in small).... when is ON, the current cuts off and the motor stops spinning, that will save your main gear if you switch it right before crashing., no matter where your throttle stick is, while the HOLD switch (autorotation) is ON, the motor won't spin, servos and gyro will work, that is also used to do autorotations.