DexWrist: A Robotic Wrist for Constrained and Dynamic Manipulation

TL;DR

DexWrist is a compact, backdrivable robotic wrist designed to improve manipulation in constrained environments and contact-rich tasks, demonstrating significant performance enhancements over traditional wrists.

Contribution

The paper introduces DexWrist, a novel robotic wrist combining quasi-direct drive actuation with a decoupled kinematic mechanism, enabling better manipulation capabilities in complex environments.

Findings

Achieved 3.75 Nm rated torque and 10.15 Hz torque bandwidth.

Increased workspace and contact stability in cluttered environments.

Improved success rates by 50-76% and reduced task times by 3-5x.

Abstract

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.