Page Comparison

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Mobility analysis of this mechanism shows there are 7 linkages, 8 joints, 1 half joint, and 1 grounding. Using equation 1 yields that this system has 1 degree of freedom

DOF = 3 L - 2 J - 1 HJ - 3

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G       (1)

Initial motion analysis of the first iteration design meets the design goals fairly well but still has room for improvement. In figure 4, the output position profile at the bottom demonstrates that the mechanism has a relatively high step distance. However it should also be noted that the output motion is not very flat along the bottom. While the bottom section is generally oriented horizontally, there is a significant curve to it that will need to be removed.

Figure 4.
First iteration mechanism and position profiles
(Click image to see animation)

In the second design iteration, shown below in FIgure 5, the mechanism’s geometry was altered to create a flatter base profile while maintaining a sufficient change in height from when the foot is in contact with the ground to when it is not. However, one issue with this motion profile comes from the rate at which the foot lifts off the ground; this could present a risk for the mechanism while it is traversing a rocky surface. Ideally, the max height of the foot would occur towards the middle of the base profile. Although the main issue of a non-flat base profile was removed with this profile, it is not evident that the pros of this profile outweigh the cons.

Figure 5.
Second iteration mechanism and position profiles
(Click image to see animation)

Position Profile:

In figure 6, the positional set of each joint is mapped to their corresponding x and y position. It can be seen when comparing to the first design iteration, that the only notable change is in Point C and the foot tip. As mentioned above, the positional profile of the foot tip matches more closely with the desired profile; however, to change the foot tip’s profile, the position of point C, located at the obtuse angle of the leftmost ternary link, and the position of point E had to be altered, as the position of the foot tip corresponds with these two positions. Since point E’s profile can only change in magnitude and size, but cannot change geometry, as it is linked to the ground, the main difference comes from Point C, and this is evident when contrasting it to the previous position profile.

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Next Section:  Kinematic Analysis and Design Process