The JOD's are simply motor driven gearboxes that allow the basic structure of the arm to articulate much like the human arm. SRMS is much more articulate than even the human arm and can therefore accomplish very complex manoeuvres. The JOD motors are equipped with their own brakes and joint motor speed control. Each JOD also incorporates a device called an encoder, which accurately measures joint angles. Thus each joint is capable of moving independently at different speeds and in different directions with respect to any or all the other JOD's.
Booms Linking the shoulder, elbow and wrist joints are the upper and lower arm booms.
These booms are constructed of graphite-epoxy. The upper arm boom is approximately 5 m. long by 33 cm. The lower arm boom is approximately 5.8 m. long by 33 cm. This link continues from the SRMS in the payload bay and continues on into cabin of the space shuttle where astronauts control the actions of the arm remotely. The forces developed by the End Effector on the payload through the grapple probe will allow for manoeuvring of the payload without separation from the remainder of the SRMS to the positional accuracy's previously stated.