tailieunhanh - LEGO MINDSTORMS - The Unofficial Guide to Robots - Jonathan B. Knudsen Part 7

Tham khảo tài liệu 'lego mindstorms - the unofficial guide to robots - jonathan b. knudsen part 7', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 110 Figure 5-6. Linking shafts with pulleys and a band On the other hand you can use pulley slippage to your advantage. If part of your robot should have a limited range of motion like a trap door that opens and closes a pulley can be very useful. You can run the motor for longer than it actually takes to open or close the door when the door has gone as far as it can go the pulley band will simply slip. In the final design a pair of pulleys is used to link the arm motor to the arm worm gear shaft. You can see this arrangement on the top of Minerva just look for the white band. Note that this band does not slip in general. Its motion is geared down so far that the arm is likely to break apart before the pulley starts to slip. Mechanical Design Several thorny mechanical issues complicate the design and construction of Minerva. In this section I ll talk about some of Minerva s more interesting mechanical features. Grabber Arm Minerva s grabber arm is operated by a single motor. If you run the motor in one direction the arm lowers the grabber grabs and the arm rises again. Run the motor in the opposite direction and the arm lowers the grabber relaxes and the arm rises once again. This mechanical sorcery is based on the FetchBot created by Ben Williamson see the Online Resources section for details . A cutaway view of the arm is shown in Figure 5-7. The entire arm is controlled by the main drive shaft. A motor linked to a worm gear drives the 40t gear on the main drive shaft. 111 Figure 5-7. Cutaway view of the grabber arm The key to understanding how the arm works is that it moves up and down for two separate reasons 1. The cams on the lower shaft push the arm up and let it move back down. 2. When the grabber grips something the geartrain that controls the grabber locks up. When the main drive shaft continues turning it moves the entire arm up and down. Suppose Minerva begins with her arm raised and the grabber open. When the main drive shaft starts turning .