Saturday, June 15, 2013

Squaring the LEGO World: Vertical Bracing

Welcome back Lego Mindstorms NXT hobbyist... We continue our discuss about building robots with lego mindstorms NXT past time. Why do we care about all these relationships? To answer this, we must travel back to the late 1970s when the LEGO TECHNIC line was created. Up to that time, LEGO was designed and used to build things made of horizontal layers: Bricks and plates integrate pretty well when stacked together. Every child soon learns that three plates count for a brick, and this is all they need to know. But in 1977, LEGO decided to introduce a new line of products targeting an older audience: LEGO TECHNIC. It turned the common 1 x N brick holes into what we call a TECHNIC brick, or a beam (Figure 1.5, left). These holes allow axles to pass through them, and permit the beams to be connected to each other via pegs, thus creating a whole new world of possibilities.

In the late 1990s, the advent of studless beams (Figure 1.5, right) opened the door to alternative building options. One of the best sets in TECHNIC history is undoubtedly the 8448 Super Street Sensation, which is built almost entirely from studless parts. LEGO was clever with its approach here. Instead of using beams to construct the chassis and plates to provide the "shell" or "form" for the model, the chassis was built using studless beams and its style was handled by fairing panels, allowing the curves of the car to "flow" with the design. LEGO did this to reduce costs: Less material required equals a cost savings in production. You can see a great example of this if you compare the 8448 Super Street Sensation to the classic TECHNIC 8880 Supercar. Compare their approaches to construction, and their weight.You will notice significant differences. The 8880 gets all its design cues from classic TECHNIC beams, whereas the 8448 uses fairings and flex axles for its design.

Figure 1.5 The LEGO TECHNIC Beams

Lego Mindstorms NXT hobbyist, Suppose you want to mount a beam in a vertical position to brace two or more layers of horizontal beams. Here's where you must remember the 6:5 ratio. The holes inside a beam are spaced at exactly the same distance as the studs, but are shifted over by half a stud. So, when we stand the beams up, the holes follow the horizontal units and not the vertical ones. Consequently, they don't match the corresponding holes of the layered beams. In other words, the holes in the vertical beam cannot line up with the holes in the stack because of the 6:5 ratio.At least not with all the holes. But let's take a closer look at what happens. Count the vertical units by multiples of 6 (6, 12, 18, 24, 30...) and the horizontal ones by multiples of 5 (5, 10, 15, 20, 25, 30...). Don't count the starting brick and the starting hole~that is your reference point; you are measuring the distances from that point.You see? After counting five vertical units you reach 30, which is the same number you reach after counting six horizontal units (see Figure 1.6). 

Figure 1.6 Matching Horizontal and Vertical Beams

Now suppose lego mindstorms nxt hobbyist want to construct a robot that needs to be strong but light. With the studded beams, you would have to use a number of beams, plates, and pins to create the frame, and potentially you would need to cross-brace it. Depending on the approach taken, you may even use the aforementioned stacking technique, which would make your robot strong but heavy. With some of the newer parts that are now available, creating a strong and light chassis is quite simple and straightforward. Figure 1.7 shows a sample chassis that you could use as a base for your robot. It employs very few pieces, and in fact, it uses only four unique parts (in quantity) to make for a solid structure.

Figure 1.7 Sample Chassis

Ok, LEGO mindstorms NXT hobbyist.. see you latter about Tilting The LEGO World: Diagonal Bracing

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