The performance of the CPGs is evaluated using a physical
simulation, which is run over a 5 s time interval. The fitness
function is then computed as the distance between the achieved
position of the pivot modules and a desired position. In the
experiment, the desired position is 7 map units away from the
initial position of the robot in the direction of the desired motion.
For example, for optimization of the ‘go-left’ motion, the desired
goal position is 7 map units to the left of the robot. The primitives
found for the desired positions are depicted on Fig. 5. The basic PSO
algorithm is employed with 30 particles and 200 iterations.