DOF, joints and motors—what is the difference?
A bigger number does not automatically mean a better hand.
Distinguish joint count, motion freedom and actuator count.
Three counts to keep separate
A joint is a mechanical connection. A degree of freedom is an independent motion coordinate. An actuator produces motion or force. Coupling can make several joints move together, so these counts need not match.
Read a specification carefully
Manufacturers use “active DOF” and “total DOF” differently. Check the mechanism and what is independently controlled. In our directory, an unknown value is a dash, never zero.
Try a comparison
Choose two hands. Compare their fingertip reach, sensing and software alongside DOF. Write one task where the extra movement might help—and one where it might not.
Try it yourself
FINGER MOTION LAB · two-joint approximation
One finger, two joints. How many independent motions?
2 joints · 2 independent coordinates
This diagram isolates two joints of one finger; it is not a whole hand. The coupled mode imposes an exact constraint. Real underactuated hands may have additional passive or compliant motion. This diagram does not model contact, torque or any commercial hand.
Your practical task
- Move the two angles separately in independent mode.
- Switch to coupled mode and change the first angle.
- Explain why the second joint still moves even though it has no independent slider.
What to produce: A comparison of two joints with one versus two independent coordinates.
Check your understanding
Original sources & next steps
MuJoCo: coordinates, joints and actuation ↗Original Dexhands teaching material. Interactive models and added references reviewed September 23, 2026; the introductory reading retains its September 22 review. Research links are not endorsements or evidence of hardware compatibility.