Quadrupedal Simulation: Preliminary Results

The initial work on a quadrupedal simulator has concentrated on the spontaneous generation of symmetrical gaits. The simulator uses the Dynamechs C++ library and a finite state Central Pattern Generator (CPG) controlled by a genetic algorithm based optimisation system. The dimensions and inertial parameters of the model are based on the Poser 5 horse geometric model scaled and checked against the experimental data in Buchner et al. (1997). The muscle dimensions are taken from Payne (personal communication) and Brown et al. (2003). The CPG has been adapted from our previously published bipedal version (Sellers et al 2003) to allow it to control the extra pair of limbs allowing loose coupling and limited control of the phase relationship between the fore- and hindlimbs. As before an initial step was produced by setting the modelling parameters by hand although this was considerably more difficult than in the bipedal case. The simulator was then allowed to evolve efficient walking with the starting conditions for a run taken from the best previous run (Sellers et al 2004). Unlike our previous work these simulations are fully three-dimensional with the only compromise being that the hip and shoulder joints are modelled as hinges rather than ball-and socket. The model is thus free to fall over in any direction it chooses and is not constrained to travel in any particular direction although it starts off facing forward.

The preliminary results from a limited number of trials are as follows:

References

Sellers WI, Dennis LA, Wang W, Crompton RH. Evaluating alternative gait strategies using evolutionary robotics. Journal of Anatomy. 2004 204: 343-351.

Sellers WI, Dennis LA, Crompton RH. Predicting the metabolic energy costs of bipedalism using evolutionary robotics. Journal of Experimental Biology. 2003 206:1127-36.

Brown NA, Kawcak CE, McIlwraith CW, Pandy MG. Architectural properties of distal forelimb muscles in horses, Equus caballus. Journal of Morphology 2003 258:106-14.

Buchner HH, Savelberg HH, Schamhardt HC, Barneveld A. Inertial properties of Dutch Warmblood horses. Journal of Biomechanics 1997 30:653-8.