...
From the second prototype we learned that the 3D printed pin joints quickly wear down and become too loose to be functional so we decided to design snapping joints. The snapping joints are compliant enough to deflect to enter the pin joint hole and the tabs on the end keep the links from coming off the joints even when loosened over time. These worked much better keeping the links togetherthen the original pin joints. The other big main design change was to move the location of the elastic that helped to keep the claw closed. Initially it was thought that the bottle could move aside the elastic in, but it the surgical tubing was too strong. So Because of this we moved the elastic out of the claw entirely for the final design. The surgical tubing was replaced with a rubber band to reduce the force required to actuate because of the need to use a servo to actuate the claw due to weight considerations for the armthe claw so that a servo could open it. This was needed because the motor driving the arm was not powerful enough to drive the arm with the mass of a motor at its end. Teeth were added to the claw for aesthetics. The final design is capable of grabbing a plastic bottle and can in an upright position and a can laying down.
...