Legs description

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All robot's legs are instances of a single mechanism (the well known pantograph mechanism [1]) but the simulator allow to fix the parameters of this mechanism for each particular robot.

Figure 2.28 shows a schematic representation of a leg with its attached frame of reference. The three controllable dof of the leg correspond to the angles $\alpha$, $\beta$, and $\gamma$. $\alpha$ is the angle between segment 1 and the axis Y, $\beta$ is the angle between segment 2 and the vertical, and $\gamma$corresponds to the rotation angle around the Z axis. Observe that if we modify angle $\alpha$ segment 1 is moved but segment 2 is also move so that angle $\beta$ is maintained.

  

Figure 2.28: The leg structure. Angles point toward its positive sense.

In the leg positioning section of legs description we have to indicate the point at which legs are attached to the body and the leg orientation. Leg placements must be given clockwise (from a top view of the robot) starting from any leg and for each each one of them we have to indicate:

• An identifier: Just a number from 0 to $number\_of\_legs-1$ to refer to the leg. This is the leg number used in all the robot functions described in next chapter.
• An attaching point: The (x, y, z) coordinate of the robots body to which the leg is attached.
• A rotation angle around the Z axis of the robot along which segment 1 is aligned.

After the global description of the leg arrangement we have to include some configuration parameters that are used for all legs. First, we have to indicate the leg bump tolerance. This parameter is used to determine whether a leg is touching of inside the ground. This measure is suppose to correspond to the passive adaptation capacity of the leg. Next we can can indicate the sizes of each leg segment. For each segment three variables can be set: the length (l in figure 2.28), the wide (w),and the height (h). The last leg configuration subsection includes restrictions to the ranges of each dof (angles $\alpha$, $\beta$, and $\gamma$). There is an additional restriction that can be imposed over the angle between segments 1 and 2 (angle $\delta$ in figure 2.28).