This paper proposes a new light-weight spatial tensegrity joint mechanism to be used in serial manipulators. The mechanism uses a simple architecture of bars, cables, platforms and spherical joints, making it lightweight and suitable for integration into a stack of robot designs. We start with a 3-degree-of-freedom (DOF) mechanism actuated by 3 cables and we add an additionnal passive cable taught at a suitable tension to ensure stability and to limit the number of DOF to 2.