To denote a significantly different design, the first digit of the prototype number was adjusted from J1 to J2. J2 was not pursued, and not documented. J3 is documented here.

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J3 aimed to remove many of the issues with the J1 prototypes by replacing the hinge with a ball bearing. To do this, segments J3.22 and J3.23 were each split into two pieces. (J3.22 is 

demonstrated in the image to the right). The design allowed for a small ball bearing to be friction fit between the pieces.

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Notes:

This design functioned significantly better than the J1 sets, and was much more durable. However, the tolerances added were not enough, and there were places that the resin still rubbed. In addition, due to error in the printing process places where the tendon channel was printed in one piece, rather than being split in half lengthwise, the channel did not print correctly and was completely blocked off in places. This is likely due to resin getting trapped in the channels, since the channels were so small. 

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Recommendations:

Increase tolerances on all places that segments can rub, and increase the width of the channels so that the resin can drain while printing.