Skip to main content

Hand Design: DOF, Actuation, and the 22-DOF Target

Duration: 55 min · Level: Advanced · Module: 6. Dexterous Manipulation · Focus: hands, dexterity, DOF, design

Learning objectives

By the end of this lesson you will be able to explain and apply:

  • Human hand DOF breakdown
  • Tendon-driven hands (Shadow, Dexterous Hand)
  • Direct-drive hands (LEAP Hand)
  • LEAP Hand (Carnegie Mellon 2023)
  • Inspire Hands (used in Unitree G1 upgrade kit)

Why this matters​

The human hand has 27 bones, 29 joints, and over 30 muscles — producing 21 controllable DOF and extraordinary dexterity.

Overview​

The human hand has 27 bones, 29 joints, and over 30 muscles — producing 21 controllable DOF and extraordinary dexterity. Modern robot hands target 16-22 DOF as a practical compromise between capability and cost/weight. Figure 02 and Tesla Optimus Gen 2 both chose 22 DOF as the G1 target.

Key concepts​

Key idea

Human hand DOF breakdown: 4 fingers × 4 DOF (MCP flexion/extension, MCP ab/adduction, PIP, DIP) + thumb × 5 DOF = 21 DOF total

  • Tendon-driven hands (Shadow, Dexterous Hand): motors proximal to hand, cables run through fingers; lightweight fingers but complex routing; Shadow Hand has 20 DOF
  • Direct-drive hands (LEAP Hand): small actuators at each joint; heavier fingers but simpler control and more transparent force feedback; LEAP Hand: 16 DOF, $4k
  • LEAP Hand (Carnegie Mellon 2023): open-source, 3D-printable, affordable; used extensively in research; matches human-scale manipulation in most tasks
  • Inspire Hands (used in Unitree G1 upgrade kit): 12 DOF, good dexterity, ~$8k/pair; commercially available with ROS support
  • G1 hand specification: 22 DOF minimum for healthcare; tendon-driven preferred for finger weight reduction; custom tactile sensing on all 10 fingertips required

Check your understanding​

Try to recall each answer before expanding it.

Q1. What do you know about Human hand DOF breakdown?

4 fingers × 4 DOF (MCP flexion/extension, MCP ab/adduction, PIP, DIP) + thumb × 5 DOF = 21 DOF total

Q2. What do you know about Tendon-driven hands (Shadow, Dexterous Hand)?

motors proximal to hand, cables run through fingers; lightweight fingers but complex routing; Shadow Hand has 20 DOF

Q3. What do you know about Direct-drive hands (LEAP Hand)?

small actuators at each joint; heavier fingers but simpler control and more transparent force feedback; LEAP Hand: 16 DOF, $4k

Q4. What do you know about LEAP Hand (Carnegie Mellon 2023)?

open-source, 3D-printable, affordable; used extensively in research; matches human-scale manipulation in most tasks

Q5. What do you know about Inspire Hands (used in Unitree G1 upgrade kit)?

12 DOF, good dexterity, ~$8k/pair; commercially available with ROS support

References​

  • LEAP Hand: Low-Cost, Efficient, and Anthropomorphic Hand for Robot Learning — Shaw et al. (2023). RSS 2023

Next: 6.2 Tactile Sensing: GelSight, DIGIT, and BioTac →

Part of Module 6: Dexterous Manipulation.