Figure 8. The large variation in tripod geometry can explain why insects that employ a tripod gait have varying speed and kinematics.
Two parameters that affect the stiffness of an animal walking on a tripod are the nondimensionalized stiffness of each leg (γ) and the geometry of the tripod defined by the ratio L/rm. (A) The curve divides the γ-L/rm plane into two regions with either fly-like or cockroach-like kinematics. The data points show the values from fits to the fly data. The alphabets represent approximate L/rm ratio for a few insects as noted below. Most insects have an L/rm ratio near the minimum of the curve, making it more likely that they can achieve an inverted fly-like kinematic profile. (B) Plot of leg spring constant as a function of L/rm ratio. Many insects have L/rm ratio such that changes in L/rm ratio can affect γs. Cockroaches have L/rm ratio where changes in geometry would have little effect on the spring constant.
a=Formica polyctena; b=Formica pratensis; c=Carausius morosus; d=Aretaon asperrimus; e=Medauroidea extradentata; f=Periplaneta americana; g=Blaberus discoidalis.