6-DOF Arm: Exploded View
This is the arm from our homepage, shown as an assembly of parts. Click a part to read its function. Move the slider to open the stack. Drag the view to turn it.
PARTS_LIST // CLICK A ROW
Select a part
Click a part in the view, or click a row in this list.
Each part of the arm is one of two things. A link is a rigid body. A joint permits motion between two links. The exploded view separates the parts, so you can see each one.
Count the mobility
The arm has 7 links. This count includes the ground. It has 6 revolute joints. Each revolute joint permits 1 freedom, so it removes 5. Apply the spatial Kutzbach equation from the notes:
$$ M = 6(L - 1) - \sum_{i=1}^{5} (6 - f_i)\,J_i = 6(7 - 1) - 5(6) = 6 $$
The result is 6 degrees of freedom: one for each joint. Six freedoms put the tool at each position and each orientation in the workspace. The course notes, Chapter 1, give the full derivation.