We ordered 96 pieces of plastic glasses, glued them except the top ones, contained new bits and glued top ones again. Finally there were beautiful 16 cubes! And as we tested, we attached copper tapes on one corner of the bottom of the cube like this picture. This tape was going to connect two wires - power and ground- on the tray like a switch. Actually, we expected really good connections with it but it did not work well. Because the cube's surface was so flat and hard, so if two wire, power and ground, on the tray were not even, this connector could not touch both of them in other words it could not close a switch.
We needed more cushioned or more flexable connectors. After trying many different ways, we decided to attach two wires on the copper tape as a cross. Because it was an easest way to fix this problem, but if we had more time, it might be better to look for a neater way. But it helped connections pretty well. Here is a picture of a new connector.