A coupling and control assembly including a sensor for providing an electrical signal for electronic transmission control, the assembly comprising: a controllable coupling assembly including first and second coupling members supported for rotation relative to one another about a rotational axis , the first coupling member having a first coupling face oriented to face radially with respect to the axis , the second coupling member having a second coupling face oriented to face radially with respect to the axis and having a set of ferromagnetic or magnetic locking formations , the first and second members being positioned relative to each other so that a locking element (152; 152'; 152") and the sensor are in close-spaced opposition to the locking formations ; and an electromechanical component including a reciprocating member (170; 170'; 170") configured to move the locking element (152; 152'; 152") in response to the component (114; 114') receiving an electrical control signal, the locking element (152; 152'; 152") abuttingly engaging one of the locking formations in a coupling position of the locking element (152; 152'; 152") to prevent relative rotation in one direction about the axis , the sensor sensing magnetic flux to produce an electrical output signal indicative of a speed of the relative rotation wherein a variable magnetic field is generated in response to rotation of the locking formations past the sensor , characterised by ; the first coupling member comprises the locking element (152; 152'; 152") and the sensor , and wherein the component (114; 114') is supported so that the reciprocating member (170; 170'; 170") is configured to move the locking element (152; 152'; 152") across a gap between the coupling faces . a controllable coupling assembly including first and second coupling members supported for rotation relative to one another about a rotational axis , the first coupling member having a first coupling face oriented to face radially with respect to the axis , the second coupling member having a second coupling face oriented to face radially with respect to the axis and having a set of ferromagnetic or magnetic locking formations , the first and second members being positioned relative to each other so that a locking element (152; 152'; 152") and the sensor are in close-spaced opposition to the locking formations ; and an electromechanical component including a reciprocating member (170; 170'; 170") configured to move the locking element (152; 152'; 152") in response to the component (114; 114') receiving an electrical control signal, the locking element (152; 152'; 152") abuttingly engaging one of the locking formations in a coupling position of the locking element (152; 152'; 152") to prevent relative rotation in one direction about the axis , the sensor sensing magnetic flux to produce an electrical output signal indicative of a speed of the relative rotation wherein a variable magnetic field is generated in response to rotation of the locking formations past the sensor , characterised by ; the first coupling member comprises the locking element (152; 152'; 152") and the sensor , and wherein the component (114; 114') is supported so that the reciprocating member (170; 170'; 170") is configured to move the locking element (152; 152'; 152") across a gap between the coupling faces . <EOS>