I am trying to find the forward kinematics of this manipulator in the picture using DH notation. All of the joints are rotational.

Manipulator picture

I managed to get to the third joint. The parameter table is below.

Joint Theta d a alpha
1 q_1 d_1 0 pi/2
2 q_2 0 d_2 0
3 q_3 0 d_3

I am not sure what the alpha for joint 3 should be. Any help would be appreciated.

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    – Tully
    Commented Apr 20, 2023 at 15:32

1 Answer 1


I would suggest watching Robotics 1 U1 (Kinematics) S5 (HTM) P2 (HTM by Denavit Hartenberg), to learn how to find DH-parameter table.

Alpha values can be found out by the rotation of the first frame to the second frame's x-axis to match the z-axis with second frame. Therefore, here the alpha value for joint-3 would be pi/2 when we rotate frame 3 around frame 4's x-axis to match the z-axis.


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