Martin Peticco

Martin Peticco, Gabriella Ulloa, John Marangola et al.

Development of dexterous manipulation hardware has primarily focused on hands and grippers. However, these end-effectors are often paired with bulky and highly stiff wrists that limit performance in human environments. More designs have adopted backdrivable actuation, but are still difficult to model and control due to coupled kinematics or high mechanical inertia from heavy links. We present DexWrist, a robotic wrist that advances manipulation in highly constrained environments and enables dynamic, contact-rich tasks. We achieve this by combining quasi-direct drive actuation with a decoupled parallel kinematic mechanism in a compact design. It delivers 3.75 +/- 0.05 Nm rated torque, 0.33 +/- 0.06 Nm backdrive torque, 10.15 +/- 1.34 Hz torque bandwidth, +/- 40 degrees ROM in both DOFs, and a one-to-one motor-to-DOF mapping in a 0.97 kg package. In practice, these properties increase workspace in cluttered environments and stabilize contact without the need for finely tuned admittance control. We evaluate DexWrist as a drop-in wrist upgrade in simulation and on two robot arms performing representative constrained and contact-rich tasks. In learned policy evaluations, DexWrist achieved 50-76% relative improvements in success rate, and reduced autonomous task completion times by 3-5x. More details about DexWrist can be found at https://dexwrist.csail.mit.edu.

Martin Peticco, Pulkit Agrawal

Traditional robotic hand metrics focus on static properties such as workspace, manipulability, and grasp stability. However, these metrics do not directly measure dexterity under the standard definition in robotic manipulation: the ability to continuously change an object's pose within the hand while maintaining contact from an initial grasp. We introduce Kinematic Rolling Manipulation Ability (KaRMA), a kinematic-only metric for fine manipulation that quantifies reachable in-hand translation and reorientation of a spherical test object within a two-finger precision pinch through feasible rolling motions. KaRMA enforces joint limits, collision constraints, rolling contact, and antipodal force feasibility, then investigates reachable in-hand object poses via breadth-first search over translation and rotation primitives. KaRMA reports three scores: translational coverage (KaRMA-T), rotational coverage (KaRMA-R), and sensitivity to the initial grasp (KaRMA-S). We evaluate KaRMA on 16 widely used robotic hands and compare against static baselines, showing that KaRMA separates hands that rank identically under static proxies, reveals translation-rotation tradeoffs invisible to existing baselines, and is qualitatively consistent with selected published task benchmarks where Jacobian-based metrics can be misleading.

Nolan Fey, Gabriel B. Margolis, Martin Peticco et al.

Achieving athletic loco-manipulation on robots requires moving beyond traditional tracking rewards - which simply guide the robot along a reference trajectory - to task rewards that drive truly dynamic, goal-oriented behaviors. Commands such as "throw the ball as far as you can" or "lift the weight as quickly as possible" compel the robot to exhibit the agility and power inherent in athletic performance. However, training solely with task rewards introduces two major challenges: these rewards are prone to exploitation (reward hacking), and the exploration process can lack sufficient direction. To address these issues, we propose a two-stage training pipeline. First, we introduce the Unsupervised Actuator Net (UAN), which leverages real-world data to bridge the sim-to-real gap for complex actuation mechanisms without requiring access to torque sensing. UAN mitigates reward hacking by ensuring that the learned behaviors remain robust and transferable. Second, we use a pre-training and fine-tuning strategy that leverages reference trajectories as initial hints to guide exploration. With these innovations, our robot athlete learns to lift, throw, and drag with remarkable fidelity from simulation to reality.