This robot arm closely resembles the arm that appears in the RIS 2.0 (RCX) set (#3804). But since the NXT set has three motors instead of only two, this design uses independent motors for grabbing and lifting. A third motor is used to rotate on its base. An ultrasonic sensor is mounted on the robot to enable it to see objects.
When I built this robot in January 2007, I probably didn’t quite understand how the original RIS 2.0 robot arm worked. You can see a set of big gears in the middle section of the arm. As it turns out, these are superfluous as long as you lock only one of them to the arm’s middle section. The RCX arm needed the gears to open and close the non-motorized grabber.
It’s funny that when people copy someone else’s design, they also copy the errors. For instance, this robot arm on Youtube has the same superfluous gears. Check out the pictures below to make your own copy.
