Modified Design of a Precision Planter For a Robotic Assistant Farmer

External loads and boundary condition: Figure 4-8 shows the external loads and the 
support for disc holder. This part is attached to the chassis by bolts; so face A is assumed to be 
fixed support. Load B and C are the reaction forces of the depth control link, and they are 
calculated at previous section. But they are applied in opposite direction and are applied to the 
center of the holes as remote forces. Forces E, D and F are the disc forces in the horizontal, 
vertical and lateral direction, respectively. These forces are applied to the point that the disc is in 
contact with the soil. They will cause moment about the point that the disc is mounted. That is 
the reason that in figure 4-8 the forces D, E and F are defined as remote force and they are 
applied away from the point the disc is mounted. The effect of these forces will be applied to the 
point that the axis of disc is attached.

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87 
Figure 4- 8- Geometry, forces and support of the disc holder part 
Solution and result discussion: The stress contour for disc holder with the meshing 
shown in figure 4-8, is presented in figure 4-9. 
Changing the mesh size to find the real value for maximum equivalent stress showed that 
it is equal to 180 MPa. Since the material is structural steel, it has a yield strength of 250 MPa. 
This means a safety factor of 1.4 for this part. 

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88 
Figure 4- 9- Equivalent (Von Mises) Stress contour for disc holder 
The reaction forces and moments on the support for this part can be found in table 4-3. 
Table 4- 3- Reaction forces and moments for disc holder 
Support A 
Force (N) 
Moment (N.m) 
X 
1241.4 
-129.77 
Y 
-300 
329.94 
Z 
1061 
261.66 
Total 
1660.3 
440.64