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Representative input shape
Like conventional walking mechanisms, a nearly perfectly flat position profile along the bottom is ideal however there are some extra considerations. Making a walking mechanism for lunar applications also warrants a design that has a large step height. This is primarily needed for obstacle avoidance on uneven or rocky terrain to prevent the foot from getting caught on terrain during its return motion. The figure below shows an example of an acceptable output position profile. Notice how the bottom of the profile is flat and the return path above has a large clearance height.
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Second iteration mechanism and position profiles
Position ProfilesProfile:
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.
Figure 6.
Velocity ProfilesProfile:
Analyzing the velocity of the foot point as a function of the crank input angle yields the graph in figure 7. It was determined that the foot contacts the ground for input angles between ~1.0 radians and ~2.7 radians. The velocity profile shows that the foot is moving at approximately 1.4 units / sec at the beginning of ground contact and slows down to a minimum of around 0.5 units / sec mid stroke before speeding up to around 5.5 units / sec by the end of ground contact. The return stroke then starts with a high velocity back to the beginning. It should be noted that figure 7 was simulated using a 1 rad/s input angular velocity, and as such different input speeds will change the output speed.
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