Modified Design of a Precision Planter For a Robotic Assistant Farmer

Solution and results discussion: As mentioned before, this problem has been solved 
using different mesh sizes, to find out about the effect of stress concentration. Analysis showed 
that the maximum stress is happening at one of the holes, as it is shown in figure 4-16. It has 
been observed that the maximum stress is about 88 MPa. This part also has been made of 
structural steel with a yield tensile strength of 250 MPa. This will result in a safety factor of 2.85. 

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Figure 4- 16- Equivalent (Von Mises) stress contour for press wheel link 
4-2-6- vertical pull bar 
Vertical and horizontal pull bars are used to attach the planter to the robot and also for 
transportation, lifts the planter off the ground. Figure 4-17 shows the orientation of these parts 
for these two functions. Figure 4-17(a) shows the bars and winch in the straight configuration to 
do the seeding, and figure 4-17(b) shows the bars in the transportation configuration. 

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(a) 
(b) 
Figure 4- 17- (a) vertical and horizontal pull bar in seeding configuration, (b) vertical and 
horizontal pull bar in transportation configuration 
Stress analysis has been performed for both of these configurations; because forces and 
supports are different for each of them. 
Meshing: Figure 4-18 shows the meshing for vertical pull bar. Finer mesh has been used 
for the area that stress concentration is expected. This mesh is used for both analyzes. 
External loads and supports: External loads and supports are different for the pulling 
configuration and lifting configuration.

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Figure 4- 18- meshing for vertical pull bar 
In pulling configuration, the nut on the figure 4-17a is fastened and is keeping the vertical 
pull bar tight in its place. Also the bottom surface of the vertical pull bar will touch the 
horizontal pull bar and limits its motion in Y direction. It means that face A is fixed support 
(fixed by the bolt) and face E is only fixed in vertical directions (Zero displacement support).The 
external forces are draft force and normal force from the planter, which were calculated in 
chapter 3. These forces are applied on the upper part of the vertical pull bar, where the planter is 
attached (Force C and D). These forces are applied to both side of the vertical pull bar, but in 
Figure 4-20a only one side can be seen. Cylindrical support is used to define the hinge on the 
bottom at point B. Figure 4-20a shows the forces and supports for vertical pull bar in pulling 
configuration. 

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In lifting configuration, the nut is removed and the only support of the bar, is on the pin 
in point B. The force from the cable and the winch must be high enough to lift the planter off the 
ground. With calculations done in chapter 3, the tension in the cable was calculated to be T= 
3157 N. The weight, W= 980 N, and center of the mass of the planter is calculated by Solid-
works. (Figure 4-19) The weight includes the weight of the planter and the seeds inside the 
hopper.
Figure 4- 19-Forces for lift configuration of the planter 

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(a) 
(b) 
Figure 4- 20- Geometry, external loads and supports for vertical pull bar in (a) pulling 
configuration, and (b) lifting configuration 

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So, to model the vertical pull bar in lifting configuration, a cylindrical support is used for 
the hinge and the planes that the planter is attached to are fixed in X direction.(Figure 4-20b)