Hi, your aluminum cube is beautiful. My 6 yr old son has asked me to help him make a cube. So I went to the Home Depot today and looked around the plumbing and hardware sections. I only found some PVC pipe attachments but nothing with 6 knobs. I also found some nuts and bolts but I don't know which kind to get. Could you give me some idea of what to buy? I don't have very many tools at home but I do have a drill if I needed to drill through the PVC pipe and copper pipe cutters if I needed to use metal piping. Please help.
We add the BrickPi3 to the LEGO assembly.  We used the LEGO EV3 “wings” to support the BrickPi3 and make it level with the BricKuber body.  This is a good step to add 8XAA batteries to the power pack and attach the BrickPi3 power pack to the LEGO assembly.  For programming you can power the BrickPi3 via USB power to the Raspberry Pi, however to move the motors you will need to supply power with the Power Pack.        
For decorative purposes, a colorant is typically added to the plastic. The pieces of a Rubik's cube are typically black. During production, colored stickers are put on the outside of the cube to denote the color of a side. The plastics that are used during production are supplied to the manufacturer in a pellet form complete with the filler and colorants. These pellets can then be loaded into the molding machines directly. Rubix Building Products

If there are no more edges left on the top layer, then they are probably either inserted in the right place but flipped, or inserted in the wrong place. To get an edge out of somewhere it shouldn't be, just insert one of the yellow edges into that slot. This should get the edge out and on the top layer, ready for you to use the above instructions to insert correctly. Rubix Build