Methods and systems for determining and modeling admissible gripper forces are described. An example method may involve receiving data representative of a plurality of trajectories along which a robotic manipulator, while gripping one or more physical objects, previously moved the one or more objects without dropping the one or more objects. The method may also involve determining set of force vectors corresponding to the trajectories. The method may also involve determining a three-dimensional virtual model of the set, where boundaries of the model represent constraints on magnitudes of forces that are applied in a given direction to perform the trajectories. The method may then involve determining one or more subsequent trajectories that correspond to a subsequent set of force vectors that are within the boundaries of the model and along which the robotic manipulator can move a subsequent physical object at particular accelerations without dropping the subsequent object.