A robot arm for use in a haptic device comprises actuators A1-A4 mounted in fixed relation which drive an arrangement of two robot arms 126, 130 and 146, 150 that, in turn, support a tool 136. Joints 124, 144 couple the movement of the robot arms 126, 130 and 146, 150 to the actuators A1-A4 in different rotary directions to allow movement of the tool throughout a three dimensional workspace. By arranging the actuators "off board", a light, responsive haptic device is provided. The device preferably comprises a removable tool with a connector (402, 404 fig. 4) and interchangeable arms (146, 150 fig. 7), preferably facilitated by magnetic couplings (414, 416 fig. 4). Further preferably the couplings are provided with electrical connections (518, 520 fig. 5) to allow sensing and other signals to be conveyed through the robot arms, such as the output of force sensors or strain gauges (802, 804 fig. 8) mounted to the arms of the robot.
