I got an OWI Robotic arm, but was slightly disappointed at it having only horizontal position for gripper. What would be the easiest way to extend with gripper/wrist rotation, i.e. 6th degree of freedom?
Unfortunately you cannot do that. I have a OWI robotic arm too. I purchased it for my semester project to demonstrate inverse kinematics for 5 DOF. Since OWI is designed as a toy to play with, we cannot expect more from it. It just does basic movements to give us an idea how a robotic arm functions. If you are looking for a 6DOF arm i suggest you purchase another 6 DOF arm like this arm by DFRobot.