Gait analysis of Pak Biawak: a necrobot lizard built using the skeleton of an Asian water monitor (Varanus salvator )

In this paper,we consider the feasibility of mimicking the sprawling gait of a live varanid (Varanus salvator) using a necrobot (named: Pak Biawak), a robot constructed using the skeletal parts of a deceased varanid of the same species. Pak Biawak is manufactured using simple joints and components, and limb motion is coupled to passive spine bending to enable the sprawling gait. Here, we assess both the lateral and dorsal kinematics of Pak Biawak at different speeds, and compare the metrics from each to those of a similarly sized live varanid. When assessing lateral view shape metrics (stride aspect ratio, stride circularity, normalised stride swept area, normalised stride swept area perimeter), we find that Pak Biawaks gait is consistent across all speeds and the majority of Pak Biawaks lateral shape metrics are kinematically aligned with those of the live varanid. This also proves true when comparing Pak Biawaks lateral trajectory metrics (radial distance of swept area, normallised root mean squared error) against those of the live varanid, and at different speeds of sprawling. Pak Biawaks dorsal metrics include the spine bending amplitude and period, and these are not found to be significantly different to those of the live varanid, however, Pak Biawaks amplitude is affected by sprawling speed. We use three metrics to compare forward and reverse limb sweeps including, angular curvature, differential curvature, and a normalised arc length. Of these, a preponderance of highly significant differences (p[≤] 0.001) are observed on comparing the forward sweep arc length of Pak Biawak at every sprawling speed against the forward sweep arc length of the live lizard. All other kinematic metrics in the necrobot are nevertheless very close to those of the live lizard. Finally, when comparing the trackway width of Pak Biawak against the live lizard, we again find there is very close kinematic compatibility between the two, and conclude that our necrobot can be designed and manufactured to mimic the sprawling gait of a real varanid, even when using simple kinematic linkages in unison with a passive spine bending differential applied at only one central location in the necrobot spine.