Université de Sherbrooke engineers demonstrated a wearable robotic third arm that weighs about the same as a human arm. According to Evan Ackerman writing in IEEE Spectrum, waist-worn hydraulic limb "is gentle enough to pick fruit but powerful enough to punch through a wall." From his interview with project lead Catherine Véronneau:
IEEE Spectrum: Can you describe the experience of wearing the robotic arm, especially when it's moving dynamically? What does it feel like? How quickly do you get used to it?
Catherine Véronneau: That's a good question, and it is something that really needs to be explored and studied in the future! But, for now, it is still not too bad having this arm on my hips, since it's only 4.2 kg (without payload) and it is located near my center of mass (to reduce inertia). I get used to it quickly, and I can compensate for some of the movements (x, y, and z translational movements), but I still have some remaining issues to compensate for torsion movements (like if the arm is hitting a tennis ball with a racket), which is funny! We also noticed that the harness needs to be rigidly connected to the body, because if there is some backlash between the harness and the body, it can be uncomfortable.
"Robotic Third Arm Can Smash Through Walls" (IEEE Spectrum)