referring to fig1 , a base plate 10 of a robot arm is attached via an arm mount 11 to an arm actuator pack 12 . the robot arm ( not shown ) is of the type comprising a plurality of articulated links and control cables or ropes extending from the base plate to terminate at various control links for controlling the shape of the arm . each control rope 13 is wrapped around a spindle 14 of each actuator and passes through a bowden sleeve to the arm mount . ( only one control rope is shown for ease of description .) a drive pack 15 comprises thirty motors that drive the thirty spindles through quick release couplings , as described in more detail below . referring to fig2 the drive pack 15 is shown without the actuator pack . the drive elements each have a drive coupling 18 comprising a disc having a protruding ridge 16 , which are shown aligned horizontally . referring to fig3 the actuator pack contains thirty spindles 14 onto which the control cables 13 are wound . the rotational position of each spindle controls the deployed length of each cable ; the length of each cable controls the arm shape . each spindle has an actuator coupling 19 comprising a disc having a plurality of depressions 21 which are sized to receive the ridges 16 of the drive couplings 18 . the actuator couplings 19 are attached to the spindles and angularly fixed thereto by means of a key and keyway . each actuator coupling 19 is shaped so as to interface to the drive couplings 18 on the drive pack to link the angular position of each spindle to the angular position of the associated drive element or motor . the spindle box assembly includes a locking mechanism including plates 22 which allow the angular rotation of each spindle to be locked in a specific position . this enables the removal of the actuator pack and arm from the drive pack without loss of control or knowledge of the angular rotational position of each spindle . thus , an arm may be detached from the drive pack and later re - attached to the drive pack without the need for re - initialisation of the arm . a useful feature of this arrangement of the quick release mechanism is that it allows the spindle box and , by association , the arm , to be attached to the actuator pack in one of two possible orientations . these orientations would be termed left - and right - handed configurations in common robotics parlance . this property derives from the existence of an axis of revolute symmetry ( at the quick release interface ), which is located in the centre of the spindle box and in the centre of the actuator pack . fig4 shows in more detail the drive , actuator and coupling assembly for a single cable . the assembly comprises a controller 31 , an encoder 32 , a brake 33 , a motor 34 , a gearbox 35 , a mounting plate 36 , an initialisation sensor 37 and rotary flag 28 , a drive coupling 29 , an actuator coupling 30 , a ratchet 31 , bearings 32 , 33 , a control rope 13 and a control rope grip 34 . the drive coupling part is mounted on the gearbox output shaft . a toothed sensor flag is supported on the drive coupling part . the mounting plate includes location features for a reflective opto - switch . this switch , in combination with the sensor flag , is used to enable the controller to sense when the gearbox output shaft is suitably oriented to enable the drive coupling part to engage with the actuator coupling part mounted on the spindle assembly . the spindle is fitted with an actuator coupling part ( which interfaces to the drive coupling part of the assembly ). the actuator coupling part is slotted in a number of positions , in this case , 6 slots each at 30 degrees to the next , allowing 12 positions of coupling with respect to the drive coupling part , or 30 degrees between possible coupling orientations . the angle between adjacent slots must be small enough so that the spindle can be rotated to the nearest available slot without excessively deforming the arm . in this case , it was determined that 30 degrees between slots was adequate , given the size and flexibility of the arm and the elasticity of the system elements , most particularly the rope itself . the number of ratchet teeth is the same as the number of slots . the ratchet forms part of the locking mechanism ( described in more detail below ), the intention being that , regardless of which ratchet tooth is held in the locking mechanism , the front face of the actuator coupling appears to offer the same interface features to the drive coupling part . referring to fig6 , the locking mechanism for a set of spindles is controlled by movement of a slide plate 40 . in fig6 a the ratchets 31 are locked by engagement of the ratchet teeth with latches 42 provided on the end of pawls 38 . when the plate 40 moves upwardly , as shown in fig6 b and 6 c , the tail 39 of each pawl 38 is pushed up by the lower surface of each corresponding indent 41 in the plate 40 which receives the tail . thus the latches 42 move downwardly releasing the ratchets 31 and allowing the spindles to rotate . in this example , the slide plate is one of two slide plates which are , in turn , operated by a crank . thus , all 30 spindles may be locked by one operating member ( i . e . the crank ). the symmetrical arrangement of two slide plates may also enable automatic operation of the slide plates by a single electric actuator . the symmetry matches the symmetry of the spindle pack as a whole , enabling “ right - handed ” and “ left - handed ” installations of the spindle box on the actuator pack . the arrangement allows the state of the locking mechanism , which comprises a set of spindle locks , to be determined by two switches . the capacity to sense the state of the locking mechanism allows an automatic controller ( e . g . a computer and software ) to control the process of locking or unlocking the spindles . thus , an operator may request that the controller locks or unlocks the spindles and the controller can detect whether the process is complete or still under way . referring to fig7 another embodiment is shown in which an actuator pack 51 and drive pack 50 are connected together within a housing 49 . the arm 52 is stowed within the actuator pack and is advanced out of the actuator pack or retracted into the actuator pack by means of the drive elements located in the drive pack . referring to fig8 , an array of drive couplings 53 is shown , along with a spring pin 54 for making electrical connections between the actuator pack and drive pack . referring to fig9 an array of actuator couplings 55 of the actuator pack is shown with a corresponding electrical connector 56 . the actuator couplings are mounted on springs such that they may only engage with the drive coupling when the drive coupling is correctly aligned . the alignment method is to rotate each motor by a maximum of one half turn . referring to fig1 the arrangement for a single cable is shown in more detail . the arrangement comprises an encoder 101 , a motor 102 , a gearbox 103 , a drive coupling 104 , an actuator coupling 105 , a spring 106 , a gear 107 , a spindle 108 , and a pulley 109 . the control rope is not shown . the control rope is secured to the spindle and follows a path to the pulley block shown in fig9 at the base of the arm before passing up through the arm . referring to fig1 another embodiment is shown in which the actuation is by linear movement of the control ropes . a ferrule 302 is attached to each control rope 205 near the proximal end of the control rope . the proximal end of the control rope is secured to an arm base plate 300 through a spring 301 , as shown in fig1 . the spring is used to ensure that the ropes do not become slack in any arm configuration . the spring also holds the section of rope between the base plate 300 and the base of the arm straight on a known line . the arm is controlled by many control ropes 205 . the actuator pack comprises a number of linear actuators one for each control rope . each linear actuator 206 is connected to a pantograph mechanism comprising two pantographs . each pantograph has two inputs 201 , 202 and one output 203 . the outputs from each pantograph are connected to a cup 209 which engages with the ferrule 302 secured to the control rope . each linear actuator is shown connected to the central inputs 201 of the pantograph . the other inputs 202 are connected to the quick release column . the linear actuator 206 is used to pull the control rope 205 . the input 202 is connected to a quick release column . for simplification only one actuator is shown . by moving the quick release column down the output will move the cup down and allow the cup to disengage from the ferrule . engagement is achieved by reversing this process . it will be appreciated that a single pantograph can be used although a different motion will be achieved . fig1 shows the arm base plate 300 and the end of arm link 305 . the end plate may have an engagement feature 307 for locating with an engagement feature in the actuator pack . the end of arm link may also have an engagement feature 312 for locating within a socket in the actuator pack housing . a skin or sleeve 308 secured to the arm may engage with the actuator pack housing at the arm socket providing a sterile boundary . referring to fig1 , in an alternative coupling arrangement , a linear rope actuator 400 is mounted on a linear slide 401 . a radially extending offset plate 402 is attached to the actuator and is equipped with a rope engagement plate 403 . the engagement plate for engaging a ferrule 413 on the rope 414 includes a spring 405 which biases the engagement plate inwardly towards the rope . only three actuators , offset plates and engagement plates are shown for clarity . when the actuator is driven to its full extent , as shown in fig1 and fig1 , contact with an end stop plate 404 causes the engagement plate 403 to pivot and retract to release the control rope ferrule 413 . the end stop may also be used as a physical datum for initialising the actuators . referring to fig1 and 18 tension is maintained in the control ropes by means of the spring 301 , which avoids wires becoming slack and ensures that the ropes are aligned with the engagement member of the actuator . the arm is equipped with an end of arm link 305 which engages with the end stop plate 404 . a sterile boundary may be created by securing the sleeve 308 to the end stop plate . the end of arm plate 300 may be equipped with electrical connectors 309 for power and data and electronics to store information within the arm . referring to fig1 the end of arm link 305 may be long enough such that the holes 500 through the end of arm link can be made long enough so that when filled with a viscous fluid the fluid will tend to remain within the hole in order to provide a seal . the holes may include features 510 to act as reservoirs for the viscous fluid .