. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. Figure 4. Strobe-shot video of a simulation of the six-legged system with negative feedback applied to all six /3 joints and positive feedback to all a and y joints. Leg positions are shown only during stance and only for each fifth time interval. In (a), straight (angle Oref = 0) and curve walking (angle 6rt., ^ 0) is shown from both a top and a side view. Walking direction is from left to right. In (b), a straight walk over an obstacle (obstacle height is 90^ of the normal body-substrate clearance) is shown from a side vie
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. Figure 4. Strobe-shot video of a simulation of the six-legged system with negative feedback applied to all six /3 joints and positive feedback to all a and y joints. Leg positions are shown only during stance and only for each fifth time interval. In (a), straight (angle Oref = 0) and curve walking (angle 6rt., ^ 0) is shown from both a top and a side view. Walking direction is from left to right. In (b), a straight walk over an obstacle (obstacle height is 90^ of the normal body-substrate clearance) is shown from a side view. In (c), three single frames (both top and side view each) of a situation in which the system was forced to fall to the ground are shown. The fall caused an extremely disordered arrangement of the legs, but within a few seconds the system stood up by itself and resumed proper coordinated walking. for each leg. In the WalkNet we implemented this such that only the a and the y joints are under positive feedback control, whereas the /3 joint remains under classical negative feedback as in the standing animal. In this way, it is possible to solve the problems mentioned above in an easy and computationally simple manner. This hypothesis is also compatible with biological results obtained from animals subject to disturbances during stance movements (Battling and Schmitz. 2000). Finally, we have to address the question of how walking speed is determined in such a positive feedback controller. We assume a central value that represents the desired walk- ing speed vref. This is compared with the actual speed, which could be derived from the optical flow or by moni-. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Marine Biological Laboratory (Woods Hole, Mass. ); Marine Biological Laboratory (Woods Hole, Mass. ). An
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