Robot Mechanisms and Mechanical Devices Illustrated - Profe Saul

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156 Chapter 4 Wheeled Vehicle Suspensions and Drivetrains Figure 4-27 Eight wheels, all fixed, center axles offset reduce the number of actuators, even with four corner steering, to eight. No known instances of this layout, shown in Figure 4-28, have been built for testing, though it seems like an effective layout. With eight wheels, there is the possibility of dividing the vehicle into two sections, each with four wheels. The two parts are then either connected through a passive joint and individually skid steered, or the joint is articulated and steering is done by bending the vehicle in the middle. This is identical to the four tracked layouts discussed and shown in chapter five. This can be a very effective layout for obstacle negotiation and crevasse crossing, but cannot turn in place. Figure 4-29 shows an example of a two-part passive joint eight-wheeled layout. Figure 4-30 adds a roll joint to aid in keeping more wheels on the ground. Another eight-wheeled layout, also applicable to a four-tracked vehicle, uses a transverse pivot, which allows the two halves to pitch up and down. It is skid steered, and is suited for bumpy terrain, but which has few obstacles it must go around. Imagine the vehicle in Figure 4-30, but with the pivot axis on its side. This layout is similar to the double rocker layout, with similar mobility and fewer moving parts. The two halves of an eight-wheeled layout can also be coupled together with a ball joint. The ball joint allows pitch, roll, and yaw between the two parts which facilitates keeping all eight wheels on the ground most of the time. The ball joint is a simple joint and can be made robust. It has a limited range of motion around two of the axis, but the third axis can rotate three hundred sixty degrees. Aligning this axis vertically aligns it in the steering axis. This allows the vehicle to have a tighter steering radius, but it cannot turn in place. Figure 4-31 shows the four-wheeled sections connected through a vertical axis ball joint. The ball joint is difficult to use with a four-wheeled vehicle because the
Chapter 4 Wheeled Vehicle Suspensions and Drivetrains 157 Eight wheels, dou- Figure 4-28 ble bogie wheel torque would try to spin the section around the wheels. This problem can be reduced if the wheels are coupled together so their torques are always nearly indentical. Figure 4-29 Two part, eight wheeled, vertical center pivot
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vi Contents Commutation 34 Installa
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viii Contents Chapter 4 Wheeled Veh
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x Contents Industrial Robots 258 In
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xii Introduction a unique robot. Wh
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xiv Introduction outdoor and indoor
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xvi Introduction Rapid prototyping
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xviii Introduction Because the phot
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xx Introduction Meanwhile, the opaq
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xxii Introduction Laminated-Object
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xxiv Introduction Figure 5 Fused De
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xxvi Introduction ton. This process
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xxviii Introduction Figure 8 Ballis
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xxx Introduction laser fusing of ce
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xxxii Introduction material to form
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4 Chapter 1 Motor and Motion Contro
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10 Chapter 1 Motor and Motion Contr
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72 Chapter 2 Indirect Power Transfe
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100 Chapter 2 Indirect Power Transf
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Page 148 and 149: 110 Chapter 3 Direct Power Transfer
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206 Chapter 7 Walkers Figure 7-4 Tw
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208 Chapter 7 Walkers and the relat
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210 Chapter 7 Walkers Figure 7-10 E
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212 Chapter 7 Walkers Figure 7-12 T
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214 Chapter 7 Walkers ROLLER-WALKER
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216 Chapter 7 Walkers Walkers have
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220 Chapter 8 Pipe Crawlers and Oth
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230 Chapter 9 Comparing Locomotion
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242 Chapter 10 Manipulator Geometri
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266 Chapter 11 Proprioceptive and E
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292 Index CAM-LEM, Inc., xxiii camm
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294 Index (ground pressure cont.) a
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296 Index (mobility systems cont.)
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298 Index shear pin torque limiters
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About the Author Paul E. Sandin is
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