Degrees of freedom: what “6-axis” and “44 DOF” actually mean

Why six is the number for arms

An object’s pose in space has six components: three coordinates for position and three angles for orientation. A serial arm with six independent joints can, within its limits, set all six. That is why most industrial and collaborative arms, including UR5e and GoFa 5, have six rotating joints.

Arms with fewer joints trade some orientation control for simplicity and speed, which suits tasks that do not need it.

Counts across robot types

Mobile and humanoid robots spend degrees of freedom on locomotion and hands as well as manipulation. NASA’s Valkyrie combines legs, arms and multi-fingered hands in its 44-DOF total.

Joint limits matter as much as the count

Two six-axis arms can move very differently. UR5e’s current datasheet lists ±360° on every joint, while ABB’s 2021 GoFa datasheet lists ±180° on five axes and −225° to +85° on axis 3. Wider ranges give more ways to reach a pose and to route cables and tools, and safety configurations can restrict them further.

More degrees of freedom are not automatically better. Each extra joint adds mass, cost, control complexity and another component to maintain. A seventh joint lets an arm reach the same pose in different ways, which helps around obstacles but needs more careful programming.

• UR5e full specifications
• ABB GoFa 5 full specifications
• UR5e vs ABB GoFa 5, compared row by row
• Spot specifications
• Valkyrie R5 specifications