Modified Design of a Precision Planter For a Robotic Assistant Farmer

4-2-2- Disc Holder 
Disc holder is the most complicated part of the planter, because of its irregular shape 
(Figure 4-7). The sources of forces applied to this part are the depth control link and the disc 
coulter. All of these forces are known and stress analysis can be performed on it. Since the 

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process of stress analysis is the same that was used for depth control link, the steps will be 
discussed briefly.
Meshing: The best meshing that was used for this part is shown in Figure 4-7. Since the 
geometry of the part is complex, tetrahedral element types was chosen by FEM program. The 
refinement of mesh on the upper corner of the part can be seen in figure 4-7. The element size in 
this area is set to 3 mm. The rest of the body has an element size of 16 mm. The number of nodes 
in figure 4-7 is 31561. The element size refinement in the corner of the body was done in order 
to study the stress concentration in that corner. When there is stress concentration in an area, a 
mesh convergence study should be performed to find out if the maximum stress result from FEM 
is “real” or not. If the maximum stress increases with finer mesh, it means there is a singular 
point in the model, which represents a mathematical singularity, not a real stress value. Instead, 
the stress at two or three elements away from that singular point remains almost constant during 
mesh refinement and may be considered as the maximum stress. There are other remedies can 
also be implement to avoid singularity in a model, such as replacing sharp corners with smooth 
curves, or use distributed loads instead of concentrated loads. To study this effect and find the 
best answer and results, different refinements on the area of stress concentration was performed 
and results were compared. These different meshing and their stress contours are shown in 
appendix B for comparison. 

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Figure 4- 7- Meshing for disc holder