barcode rendering framework c# example Figure 8-2. An early stage of JohnNXT s body development in Font

Encoder PDF-417 2d barcode in Font Figure 8-2. An early stage of JohnNXT s body development

Figure 8-2. An early stage of JohnNXT s body development
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CHAPTER 8 JOHNNXT IS ALIVE!
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The Ultrasonic Sensor alone was not big enough to shape the head, so I added some LEGO fairing panels. Other J5 parts that immediately followed in the size-matching process were the treads hubs and passive wheel. The first complete JohnNXT (version 1) still had many defects, mainly regarding the passive wheel and the upper body structure. In Figure 8-3, you can get an idea of what JohnNXT version 1 looked like.
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Figure 8-3. JohnNXT version 1, still missing some parts The top tread hubs were made with large black turntables, which are in fact dimensionally perfect when coupled with the 40-tooth gears used as ground hubs. The laser shape was primitive, but already functional. It did not just rotate about a pivot its movement was eccentric:
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CHAPTER 8 JOHNNXT IS ALIVE!
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a combination of a rotation and a translation. This rough model was the starting point that resulted in the making of the second version of JohnNXT, shown in Figure 8-4.
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Figure 8-4. JohnNXT version 2, with one of the NXT microcomputers removed
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CHAPTER 8 JOHNNXT IS ALIVE!
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The head shape was already the final one, with eyelids and positionable neck pistons. It has not been modified further in successive versions. The fingertips were made with half-cut rubber axle joiners (horror for the purists!) to get more grabbing friction. The main problems raised in this version were the laser shape, the unreliable head-driving mechanism (a slippery rubber band), and the shoulders shape. The worst problem was the fact that the treads chains escaped from the largest hubs the ones made with turntables. For the third version (see Figure 8-5), the laser was completely redesigned. The lever mechanisms allow it to lower and move toward the shoulder, or to lift and move away from it. The tread hubs were made using 40-tooth gears, sacrificing the design a bit, but eliminating the escaping chain problem. Also, the passive wheel was improved, making it as smooth as possible, to avoid influencing the treads movements with its friction on the ground.
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Figure 8-5. JohnNXT version 3, featuring new treads and laser. Notice the rubber bands added on both elbows.
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CHAPTER 8 JOHNNXT IS ALIVE!
A rubber band was added on both elbows to improve the underactuated two-DOF mechanism that allows the arms and hands to be driven by just one motor. As explained in 7, with regard to how to get more functions from a single actuator, you need one movement to be done before the other. Here, you need the arms to unfold before the hands open; the rubber band comes into play to help you. In the Johnny RCX version (similar to the Mine Sweeper grabber), the rubber band was not needed. This was because the forearm fell down under the force of gravity, because the whole arm assemblies were roughly vertical. In JohnNXT, the arms are inclined with respect to the ground, so I needed another force to make the forearms move before the hands. You can read the discussion about underactuation back in 7. The rubber band used as the transmission to drive the head was replaced with a more reliable gear train. The head motor was built inside the upper body, while the arms motor is on the side made invisible in the photo, shaping Johnny s typical toolbox. I was still not satisfied with the shoulder shape and the upper body in general. The end result is the final version 4, shown in Figure 8-6.
Figure 8-6. JohnNXT version 4, with new shoulder shape. The NXTs communicate using Bluetooth. The final version you ll build is identical, but uses the NXT high-speed serial ports to let the two bricks communicate.
CHAPTER 8 JOHNNXT IS ALIVE!
Although many things might seem to appear the same as before, there are significant differences from the previous version. The shoulders are completely redesigned to look like a cylinder. The parallelogram frame of the upper body, used to keep the shoulders and head vertical while JohnNXT raises the torso, is now dimensionally more precise. The head tended to lean backward when the torso was raised, while now the neck axis always remains vertical, whatever inclination the upper body has. The arms motor now has a structural function in the upper body. The arms motor and head motor are swapped in position. Also, the head s and arms geartrains are now different, to fit in the new frame. Finally, the treads have been structurally improved and lightened, by using a triangular frame. Could this version be the last one Could I stop with version 4 Of course not. The main reason is that this fourth version of JohnNXT has two NXTs that communicate using Bluetooth. What s wrong with it Nothing, at first glance. But, wanting to control the whole model remotely using Bluetooth (see 9), I needed to free the connection and so had to plan a different manner of communication. So, I used the mysterious high-speed serial communication implemented behind port 4 of the NXT. The external shape of JohnNXT remains the same, while a new communication protocol had to be developed to use the serial ports. So, the final version of JohnNXT, the one you ll build, is version number 5, where the version change is primarily due to the software update. It seems this number was assigned by fate! Our beloved JohnNXT can be controlled remotely via Bluetooth with a mobile phone, a PDA, or the remote control shown in 9. This concludes the development chronicle for the robot you ll build in this chapter.
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