In order for robots to interact safely and intelligently with their environment they must be able to reliably estimate and localize external contacts. This paper introduces CPF, the Contact Particle Filter, which is a general algorithm for detecting and localizing external contacts on rigid body robots without the need for external sensing. CPF finds external contact points that best explain the observed external joint torque, and returns sensible estimates even when the external torque

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... ent is corrupted with noise. We demonstrate the capability of the CPF to track multiple external contacts on a simulated Atlas robot, and compare our work to existing approaches. H(q) ∈ R nv×nv is the inertia matrix, C(q,q) ∈ R nv×nv are the Corioilis and centrifugal terms, and g(q) ∈ R nv is the gravity vector, τ are the motor torques, B maps the motor