What is Torque?
Torque is rotational force — the twisting power that makes a joint turn. In robotics, it’s measured in Newton-meters (Nm). One Nm is the torque you’d feel holding a 1-liter bottle of water at arm’s length. A humanoid hip joint might need 200–400 Nm to stand up from a crouch.
Why Torque Matters
Every movement a robot makes requires torque:
- Standing up: Hips and knees must generate enough torque to lift the robot’s weight against gravity
- Walking: Each step requires the ankle to push off the ground with controlled force
- Lifting: A shoulder joint needs torque proportional to the weight × distance from the body
- Balancing: When the robot sways, ankle actuators apply corrective torque to stay upright
Torque in Humanoid Specs
| Joint | Typical Torque Range | What It Enables |
|---|---|---|
| Hip | 200–400 Nm | Standing, crouching, recovering from pushes |
| Knee | 150–250 Nm | Walking, stairs, absorbing landing impact |
| Ankle | 100–200 Nm | Balance control, push-off, uneven terrain |
| Shoulder | 50–150 Nm | Reaching, lifting moderate objects |
| Elbow | 30–80 Nm | Manipulation, pushing, pulling |
| Wrist | 5–20 Nm | Fine grasping, tool use |
Torque vs. Speed
Motors have a trade-off: more torque usually means less speed. This is why harmonic drives and gearboxes exist — they multiply motor torque (sacrificing speed) to reach the values humanoids need.
| System | Torque | Speed | Typical Use |
|---|---|---|---|
| Direct drive motor | Low | High | Fast, light movements |
| Motor + planetary gearbox | Medium | Medium | General-purpose joints |
| Motor + harmonic drive | High | Low | Humanoid hips, shoulders |
The Bottom Line
Torque is the hidden spec behind every impressive robot video. A backflip isn’t about software — it’s about having enough torque in the right joints to explosively push off the ground. When comparing unitree-h2|Unitree H2]]|Unitree H2]] (360 Nm) to smaller platforms, the torque numbers explain the capability gap.