Runaway emergency actuator brake

An actuator comprising:

• a motor shaft having an axis (X),
• an output arranged to rotate within an angular range of less than 360 degrees, wherein rotation of the motor shaft about the axis drives the output in rotation,
• a first ratchet comprising a first ratchet wheel and a first ratchet pawl, the first ratchet arranged such that, while the first ratchet pawl engages the first ratchet wheel, the first ratchet wheel is freely rotatable in a first direction and prevented from rotation in a second direction, opposite the first direction;
• a second ratchet comprising a second ratchet wheel and a second ratchet pawl, the second ratchet arranged such that, while the second ratchet pawl engages the second ratchet wheel, the second ratchet wheel is freely rotatable in the second direction and prevented from rotation in the first direction;
• wherein the first and second ratchet wheels are mounted to a ratchet wheel shaft;
• a first cam surface connected to rotate with the output, wherein the first cam surface is arranged to disengage the first ratchet pawl from the first ratchet wheel when the output is within a first predetermined angular range, and to allow the first ratchet pawl to engage with the first ratchet wheel when the output is outside the first predetermined angular range;
• a second cam surface connected to rotate with the output, wherein the second cam surface is arranged to disengage the second ratchet pawl from the second ratchet wheel when the output is within a second predetermined angular range, and to allow the second pawl to engage with the second ratchet wheel when the output is outside the second predetermined angular range;
• and
• an electrically-actuated clutch arranged to selectively connect the ratchet wheel shaft to the motor shaft.