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Chapter 02
Basics of Animation and Forward Kinematics
Page 12
Forward Kinematics: Two Link MechanismThe mathematical drill previously done, is good for a single link mechanism only. For two link mechanism, like the robot arm, a few more considerations are required.
Consider the following example in which a 5-sided polygon is rotated for θ°
![Rotate a polygon](images/e04_c02_p12_i01_hut_rotate.jpg)
In order to rotate a polygon all the 5-points are equally rotated. If not then the shape will be deformed.
Now, instead of the polygon, imagine a 4-link mechanism. The link names are L1, L2, L3 and L4. If Link-1 is rotated then all other links after it are to be rotated:
![Only L1 is rotated](images/e04_c02_p12_i02_rotate_1_of_4link.png)
RULE:
To rotate a multi-link mechanism (graphically) along any joint, rotate all the vertices following it (with the same angle and same direction)
This can be observed from the gif-animations shown below:
![Rotate L1](images/e04_c02_p12_i03_rot_l1.gif)
To rotate L1 : Rotate Vertice_of_Joint_2, Vertice_of_Joint_3, Vertice_of_Joint_4 and Vertice_of_gripper w.r.t Vertice_of_Joint_1
![Rotate L2](images/e04_c02_p12_i04_rot_l2.gif)
To rotate L2 : Rotate Vertice_of_Joint_3, Vertice_of_Joint_4 and Vertice_of_gripper w.r.t Vertice_of_Joint_2
![Rotate L3](images/e04_c02_p12_i05_rot_l3.gif)
To rotate L3 : Rotate Vertice_of_Joint_4 and Vertice_of_gripper w.r.t Vertice_of_Joint_3
![Rotate L4](images/e04_c02_p12_i06_rot_l4.gif)
To rotate L4 : Rotate Vertice_of_gripper only w.r.t Vertice_of_Joint_4
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