# Degrees of freedom for custom made finger

I'm designing a 3D printable prosthetic hand.

Each finger has 3 joints. The first 2 joints let the finger only move in the vertical (y) direction. The final joint is like a ball and socket joint (connects finger to palm) and lets the finger rotate Up/down & left/right about 30 degrees in each direction.

Summary of 3 joints: 1 joint = finger moving in vertical (y) direction + 1 joint moving in vertical (y) direction + 1 joint rotating in vertical (y) and horizontal (x) directions

From a mechanical engineering perspective, can someone help me here by telling me how many degrees of freedom are on each finger here? How would you calculate it based on the motion I have stated above? Thanks!

I'm guessing 1 degree of freedom for the 2 vertical joints each because they only move in one dimension =2 DOF so far + 2 DOF for the rotatable joint ? = 4

• 4 sounds right to me. – Jiminion Jan 18 '16 at 19:53
• The number of degrees of freedom for a given problem in physics is a matter of choice. The better an approximation that you chose, the more degrees of freedom you will have to deal with. If you are choosing to assume that all segments of your mechanical finger are perfectly stiff, then your approximation by four angles is correct. If you let go of the assumption that you are dealing with perfectly stiff materials, then you will have to add more degrees of freedom to model the deformations. – CuriousOne Jan 19 '16 at 11:27