Slip avoidance

A robot comprising:

• at least one foot;
• a processor;
• a non-transitory computer readable medium;
• and
• program instructions stored on the non-transitory computer readable medium that, when executed by the processor, cause the robot to perform functions comprising:
• determining, by the robot, a representation of a coefficient of friction between the foot and a ground surface;
• determining, by the robot, a representation of a gradient of the ground surface;
• based on the determined representations of the coefficient of friction and the gradient, determining a threshold orientation for a target ground reaction force on the foot of the robot during a footstep of the robot;
• determining the target ground reaction force, wherein the target ground reaction force comprises a magnitude and an orientation;
• determining an adjusted ground reaction force by adjusting the orientation of the target ground reaction force to be within the determined threshold orientation;
• and
• causing the foot of the robot to apply a force on the ground surface approximately equal to and opposing the adjusted ground reaction force during the footstep.