Modular cubes
Peter Jepsen proposed this construction in the Geomag forum (unavailable at the moment):
Modular cube
440 pieces: 104 balls, 336 rods (2.47 kg)

The cube is made of twelve modules placed at its edges:
Edge module of the modular cube
32 pieces: 10 balls, 22 rods (189.40 g)

Three modules join in each vertex of the cube. They attach to one another by means of nine additional rods (red):
Three edge modules join of the modular cube

The inner space of the cube has the same geometry as a
truncated cube:
Modular cube, inside view

The construction can be extended by including several square pyramids in each edge module. In this case, we used five per edge, but parallelepipeds can be made by using a different number of pyramids for each set of four parallel edges:
Extended modular cube
1160 pieces: 284 balls, 816 rods, 60 squares (6.39 kg)

For the extended cubes or parallelepipeds may be better to consider as modules the structures resulting at the vertices:
Vertex module of the modular cube
58 pieces: 16 balls, 42 rods (335.00 g)
