Tham khảo tài liệu 'lego mindstorms - the unofficial guide to robots - jonathan b. knudsen part 4', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 50 Where s That Red Light Coming From Anyhow Isn t it odd that the light sensor an input device has a red light on it How did that happen And how is that possible with only two wires connecting the sensor to the RCX The basic role of the RCX s inputs is to measure the value of the sensor. For certain types of sensors like the light sensor the RCX also provides power to the sensor. It does this by very quickly alternating between providing power and taking a measurement. The RCX sends power to the light sensor for about 3 ms thousandths of a second and takes a measurement for about . 1 ms. It repeats this cycle over and over. These timings only apply to the standard firmware. In an alternate firmware such as legOS the timings are entirely different. Inside the light sensor an electronic circuit smooths out the pulses and provides steady power to the red light. Idler Wheels Trusty s two main drive wheels determine whether he moves forward backward or turns. But without at least one more wheel Trusty can t balance and will tip forward or backward. Trusty s third wheel is a good example of an idler wheel. An idler wheel provides support for the robot but doesn t constrain its motion. It does this by rotating freely on a vertical axis. The front wheels on shopping carts are idler wheels as are the casters under furniture. Ideally an idler wheel can easily swivel in response to changes in the robot s direction. You ve already seen Trusty s idler wheel in Figure 2-8. Make your idler wheels sturdy One of Trusty s early designs could follow a line just fine. But after about a minute of back-and-forth turning the idler wheel broke off the bottom and Trusty was left lying on his back twitching. Using Two Light Sensors You can buy more light sensors for about 20US each see the Online Resources section at the end of this chapter . By adding one more light sensor to Trusty we can simplify his program and make his movement along the black line smoother. Adding the Sensor To add .
