Fig. 6. (A) Planar model of a gecko on a flat inclined surface. is the angle of inclination and ranges from 0° (flat) to 180° (inverted). Center of mass was 2 cm above the surface and centered between the front and rear feet. A distance of 10 cm separated front and rear feet. For static equilibrium, forces in y and z and moment about x (not shown) must balance to zero. (B) Graphical description of stability margin. Given a particular point in force-space, the stability margin is shown using the frictional adhesion model (d₁) and the Kendall peel model (d₂). For the JKR model, the point shown would violate stability criteria and result in a negative stability margin. Stability margin is the minimum distance in any direction to avoid violating a constraint.