If you are anything like me, you use BrickLink, or as many call it “CrackLink” because of its addicting nature. You can find these parts there. Sometimes they are cheap, sometimes not. The parts I am talking about today are relatively cheap; I know this because I have bought hundreds of them at a time.
You can find all the parts I am talking about by searching BrickLink.com for “Technic Open Center.”
The first type is the slightly older Technic brick type. I have about a hundred each of the 6x8 and the 4x6, but only a few of the 4x4. I use them all the time because they can be used for so many things. I don’t have an exact count, but I would guess that MARVIN has about eighty in him.
First, they are great for all kinds gearboxes. You can put in a few gears and run a couple of axles through them. You can stack them by putting a couple of 1x plates between them and get a completely enclosed gearbox. You can attach a PF motor to the side and run the driving axle right into the gears. They are extremely stable and you don’t have to worry about figuring out how to attach two parallel Technic beams together.
Secondly they are great for large structures. You can pin them all together and create a large array or matrix for a floor or a base of a robot. If you put large plates on the top and bottom to link them together it becomes a super strong base. Pin a bunch of them together in a line and put some plates on them and they make a great bridge. Stack a few long beams on top of each other separated by some plates and it just gets stronger. This is how I created the long cross beams on the Lego Flexpicker. When the Flexpicker was together, the cross beams had very little sag, in fact I couldn’t see any.
The second type is the newer kind that goes by the name of “Technic Liftarm,” but I think that is a bit of a misnomer. I have never used them as a liftarm. I have only about a dozen of them and I find that they are also great for gearboxes. They have lots of holes in all directions that make it easy to attach gears and stack them. I don’t see much use in building large structures with them, but that may be only because I don’t own that many of them. If I can find some cheap, I will certainly buy them, but they are very expensive right now on Bricklink.
Your assignment, Go to BrickLink and buy some. You won't regret it.