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Hello! I am assuming you mean in URDF. If so continue reading! I had the exact same problem with a hip joint the other day.

In order to get two degrees of freedom, make TWO "revolute" joints in the same location connected via a dummy link.

Example:

link thigh_link link leg_link

link placeholder origin="0 0 0" //NOTE: this link has no change in location nor any geometry

joint hip_joint_x type="revolute" parent = "thigh_link" child = "placeholder axis xyz="1 0 0" /joint

joint hip_joint_y type="revolute" parent = "placeholder" child = "leg_link" axis xyz="0 1 0" /joint

Hope this helps!

Hello! I am assuming you mean in URDF. If so continue reading! I had the exact same problem with a hip joint the other day.

In order to get two degrees of freedom, make TWO "revolute" revolute joints in the same location connected via a dummy link.

Example:Example in Pseudo XML:

link thigh_link
link leg_link
leg_link
  
link placeholder
 origin="0 0 0" //NOTE: this link has no change in location nor any geometrygeometry
  
joint hip_joint_x type="revolute"
 parent = "thigh_link"
 child = "placeholder
"placeholder"
 axis xyz="1 0 0"
/joint/joint
  
joint hip_joint_y type="revolute"
 parent = "placeholder"
 child = "leg_link"
 axis xyz="0 1 0"
/joint/joint