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