Figure 5-3 shows the head subassembly. This assembly possesses the smaller slope, which is made out of plates and is positioned on the very front, and also the much larger liftarm slope. Besides acting as a slope, the head also gives XK2 its characteristic look—whatever that might be!
Figure 5-3. The completed head subassembly
NOTE Using plates is a common way to run under other sumo-bots, and in the non-LEGO robotic sumo world, using material similar to LEGO plates for slopes is common as well.
The head subassembly is not rigidly attached to the chassis, but instead pivots on two points. This flexibility allows the entire head to move on impact, acting as a sort of bumper (which it is). After XK2 has been completely assembled, you’ll be able to observe much more clearly how the bumper system works. But let’s quickly go over the bumper system’s operation.
Once the head has moved backwards (by getting hit), two special pieces called perpendicular axle joiners, or crossblocks, activate touch sensors, which are facing completely upside down, by running across their yellow “clickers.” (You’ll build and attach the touch sensors later in the chapter.) When the bumper—the head—is no longer being pressed inwards, two rubber bands will draw it back out.
In step 1, locate two 1x10 beams, two axle pins, four friction pins, and then position them as shown. As you might imagine, these parts lay the framework for the assembly.
Head Subassembly Step 1:Snap four friction and two axle pins into 1x10 beams.
Next in line—and shown in step 2—is the addition of two black liftarms, which are snapped onto the pins closest to the front of the beams, more pins, a 2x6 TECHNIC plate, and two 1x2 black bricks.
NOTE The RIS contains four 2x6 TECHNIC plates. All four of these are currently on the Zip-Bam-Bot chassis, but step 2 adds another one. However, you don’t need the 2x6 TECHNIC plates positioned on the front of the chassis for XK2, so you can take one of them off to use for this subassembly (the front of the chassis will be reconstructed a little later).
Head Subassembly Step 2: Add four pins, two liftarms, and a 2x6 plate with two 1x2 bricks.
In step 3, you add a few plates, which connect the two sides together, and two 1x4 beams onto the back friction pins. These beams will serve as the connection point later on, when you do the final assembly (in the “Putting XK2 Together” section).
Head Subassembly Step 3: Attach two 1x8 plates, one 2x8 plate, and two 1x4 beams.
Now for an interesting part! In this assembly, there are two rubber bands; both of them are the small, white ones included in the RIS, and both of them go in the back. You’ll add these (and other pieces) in a creative way in steps 4 through 6.
First, slide #5 axles into the beams as shown in step 4. Then position the various bushings and crossblocks on those axles.
Head Subassembly Step 4: Slide #5 axles through beams, and bushings and crossblocks onto the axles.
Once this is finished, put a white rubber band on the end of each axle. After adding the white rubber bands, place 1x2 green bricks with an axle hole and half-bushings on the last remaining spaces of the axles, thus blocking the rubber band’s only exit. You are not connecting the rubber bands to anything in particular right now; they are for later use.
Head Subassembly Step 5: Add 1x2 axle bricks, half-bushings, and two rubber bands.
Step 6 has two parts. First, place 1x3 yellow plates going from the green bricks to the beams. These plates “lock” the green bricks in place and prevent them from swinging around. Second, you’ll start working on the very front—the protruding slope part. There is not too much to this, except the pieces will be at an odd slant; well, an odd slant for most cases, but not for a sumo-bot’s slope! This slant is intentional and a good thing.
Begin by pushing a #12 axle through the black liftarms. While you’re going along, slide bushings and 1x4 beams onto the axle. The slope, which is made out of plates, will connect directly into these beams.
Head Subassembly Step 6: Add four 1x3 yellow plates and begin construction on the slope.
NOTE There are four 1x3 yellow plates used in this assembly, and the RIS has only two of them. If you do not have extra 1x3 plates, use 1x4 plates. They will project out a stud’s space on the sides, but that’s okay.
After this, snap a 6x10 plate onto the inverted 1x4 beams; this is the first piece of the slope. Also connect some 2x10 plates to the 6x10 plate—these will provide an attachment point for additional plates for the slope.
Head Subassembly Step 7: Snap a 6x10 plate with two 2x10 plates onto 1x4 beams.
Using more plates, widen the slope. Also position several plates directly above the slope, as shown in step 8. The slightly odd array of plates positioned above the slope has an important purpose: these plates, along with the 2x6 TECHNIC plate beneath them, reduce the amount of free room for the slope to a negligible amount. That means you now have a fully operable slope!
TIP Inverted (upside-down) plates provide a smooth surface, and, when combined with other plates, can form very large slopes. In other words, they’re efficient and have the potential to cover large areas with relatively few pieces.
Head Subassembly Step 8: Add two 2x8 plates, one 2x4 plate, one 1x6 plate, and two 1x4 plates.
With the slope built, the final stage of construction, for the “face,” commences. Steps 9 and 10 build up the face with liftarms, axles, pins of this and that type, and well… I think you probably get the idea.
Head Subassembly Step 9: Add four liftarms and four friction pins.
Head Subassembly Step 10: Build up liftarm slope with four 1x7 half-liftarms and add two axle pins, a #10 axle and two half-bushings.
In step 11, you begin working with the final section of the head. This step uses a large, yellow liftarm (the liftarm’s curve at the end is perfect for the head-like appearance!) and two pins. One pin is the connection point for an eye (the outer pin), and the other pin is for ribbed hosing (the inner pin).
Head Subassembly Step 11: Add large, yellow liftarm, friction pin, and axle pin.
Step 12 adds the ribbed hosing, which is the green, medium-sized type included in the RIS. When completed, the head appears as if the ribbed hosing fits perfectly, but this is actually not true. The single piece of green, ribbed hosing you add in step 12 is just a little bit wider than the head, and it pushes the yellow liftarms out to the side a little. This is okay—it will not harm or hinder XK2.
In step 13, add a yellow liftarm and a pin to the left side of the face, just as you did for the right side, and add the eyes as well—these give the sumo-bot that characteristic appearance!
TIP When adding the eyes, put the 1x1 white round plates onto the “black eye piece” first , and then attach the whole eye onto the assembly. If you do it the other way around, it will be very difficult to add the white plates.
You’re now finished with the head subassembly. It should look like Figure 5-3, shown at the beginning of this section.
Head Subassembly Step 12: Push green, ribbed hosing with friction pin into friction pin.
Head Subassembly Step 13: Add yellow liftarm and axle pin and push 2x2 round bricks with 1x1 round plates into axle pins.
This chapter is from Competitive MINDSTORMS: A Complete Guide to Robotic Sumo Using LEGO MINDSTORMS, by David Perdue (Apress, 2004, ISBN: 1590593758). Check it out at your favorite bookstore today. Buy this book now.
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