Tham khảo tài liệu 'mcgraw-hill - robot mechanisms and mechanical devices illustrated - 2003 part 8', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Chapter 4 Wheeled Vehicle Suspensions and Drivetrains 139 Figure 4-8 Reversed tricycle all drive all steer The most complicated and highest mobility three-wheeled layout is one where all wheels are powered and steered. This layout is extremely versatile providing motion in any direction without the need to be moving it can turn in place. This ability is called holonomic motion and is very useful for mobile robots because it can significantly improve mobility in cluttered terrain. Of the vehicles discussed so far all except the front steer reversed tricycle can be made holonomic if the third wheel lies on the circumference of the circle whose center is midway between the two opposing wheels and the steering or passive wheel can swing through 180 degrees. To be truly holonomic even in situations where the vehicle is enclosed on three sides like in a dead-end hallway the vehicle itself must be round. This enables it to turn at any time to find a path out of its trap. See Figure 4-8. Before we investigate four-wheeled vehicles there is a mechanism that must be at least basically understood the differential. The differential Figure 4-9 gets its name from the fact that it differentiates the rotational velocity of two wheels driven from one drive shaft. The most basic differential uses a set of gears mounted inside a larger gear but on an axis that lies along a radius of the larger gear. These gears rotate with the large gear and are coupled to the axles through crown gears on the ends of the axles. When both wheels are rolling on relatively high fric- 140 Chapter 4 Wheeled Vehicle Suspensions and Drivetrains Figure 4-9 The common and unpredictable differential tion surfaces and the vehicle is going straight the wheels rotate at the same rpm. If the vehicle turns a corner the outside wheel is traversing a longer path and therefore must be turning faster than the inside wheel. The differential facilitates this through the internal gears which rotate inside the large gear .
