# A Design of an Unmanned Electric Tractor Platform

^{*}

## Abstract

**:**

## 1. Introduction

## 2. Materials and Methods

## 3. Body Design

#### 3.1. Lightweight Design and Analysis of Car Body

#### 3.2. Fatigue Life Analysis

_{f}is the stiffness value of the front shock absorber spring, K

_{r}is the stiffness value of the rear shock absorber spring, C

_{f}is the damping value of the front shock absorber, and C

_{r}is the damping value of the rear shock absorber. The simplified suspension model was simulated by a three-dimensional two-node beam element and defined as a rigid body. In the fatigue life analysis, a three-dimensional dynamic elastoplastic finite element model was used, and the element type was eight-node hexahedral.

- A.
- Material parameters

- B.
- Loading conditions

- C.
- Boundary conditions

_{f}and K

_{r}are the stiffness of the front and rear suspension springs, respectively, which both equaled 27.5 N/mm. C

_{f}and C

_{r}are the damping values of the front and rear suspension shock absorbers whose values were set as 0.96 N.s/mm and 2.16 N.s/mm, respectively. During analysis, road signals of different levels in y direction were applied to the wheel center. Table 3 lists the parameters of the spring stiffness and shock absorber damping coefficient of the front and rear suspension systems during the fatigue life analysis.

_{e},

_{max}occurred at the hardpoint of the upper control arm of the left front suspension. The stress histories of this location, as shown in Figure 12b and Figure 13b, were respectively imported into the fe-safe software for calculation. The rain flow counting method was used to calculate the stress history of the C-and D-level road surface. The stress amplitude σ

_{a}and the number of occurrences of average stress σ

_{m}are shown in Figure 12c and Figure 13c. The fatigue life of the vehicle body obtained from the fe-safe simulation was N = 2.4 × 10

^{6}and N = 6.7 × 10

^{5}, which also means the vehicle can travel 40,724 and 11,190 km, respectively, as shown in Figure 12d and Figure 13d.

## 4. Power and System Integration

#### 4.1. Force Estimate and Power System Planning

#### 4.1.1. Force Estimate

_{q1}= f G = 0.12 × 6474.6 = 776.95 N

_{q2}required for the rotary tillage operation can be calculated, it is necessary to know the rotary tillage speed ratio λ and the soil cutting pitch S. After calculating these two values, the rotary tillage specific resistance K

_{λ}and the soil resistance F

_{L}can be obtained, and then the rotary tillage can be calculated. The driving force F

_{q2}is required for the operation. The rotary tillage speed ratio λ can be obtained by formula (2):

_{m}= 0.55 m/s is the tractor speed. After calculating the rotary tillage speed ratio λ, we obtain:

_{g}corresponding to the soil cutting pitch S and then find the correction coefficient that meets the working conditions to obtain the rotary tillage specific resistance K

_{λ}. The specific resistance K

_{λ}of the rotary tillage is:

_{λ}= K

_{g}K

_{1}K

_{2}K

_{3}K

_{4}= 15 × 0.8 × 0.95 × 0.8 × 0.66 = 6.019 N/cm

^{2}

_{g}= 15 N/cm

^{2}is the standard rotary tillage specific resistance, K

_{1}= 0.8 is the tillage depth correction coefficient, K

_{2}= 0.95 is the soil moisture content correction coefficient, K

_{4}= 0.66 is the stubble vegetation correction coefficient, and K

_{3}= 0.8 is the operation mode correction coefficient. Knowing the specific resistance of rotary tillage, we can obtain the soil resistance F

_{L}:

_{L}= 100 K

_{λ}BH = 100 × 6.019 × 1 × 12 = 7222.8 N

_{λ}and soil resistance F

_{L}, and then the rotary tillage operation time can be calculated by Formula (6) The required driving force F

_{q2}is:

_{q2}= k

_{1}F

_{L}+ f × (G + k

_{2}F

_{L})

= 0.68 × 7222.8 + 0.12 × (6474.6 + 0.74 × 7222.8)

= 6329.8 N

_{1}= 0.68 is the horizontal component coefficient, and k

_{2}= 0.74 is the vertical component coefficient.

#### 4.1.2. Power System Planning

- (1)
- Transportation operations

_{1max}= 18 km/h is the highest vehicle speed during transportation.

- (2)
- Rotary tillage operations

_{2max}= 2 km/h. Generally, the tractor used in the greenhouse requires 20 PS (15 kW) of horsepower, so two motors with a rated power of 7.5 kW were finally selected as the driving motors in this study, one for driving the tractor and the other for driving the rotary plow. Table 4 presents the specifications of the selected motor.

#### 4.1.3. Reducer Selection

- (1)
- Transportation operations

_{m}= 23.2 N·m is the motor output maximum torque, i

_{H}= 12.5 is the high gear reduction ratio, n

_{m}= 5800 rpm is the motor maximum speed, and V

_{1max}= 18 km/h is the maximum vehicle speed.

- (2)
- Rotary tillage operations

_{L}= 23.3 is the low gear reduction ratio, and V

_{2max}= 2 km/h is the maximum vehicle speed.

#### 4.2. Unmanned/Intelligent Control System Integration

#### 4.3. Vehicle System Integration and Function Testing

## 5. Conclusions

- According to the lightweight analysis process, the weight of the proposed vehicle body was 101 kg, and the bending and torsional rigidity were 11,579 N/mm and 4923 N·m/deg, respectively.
- In the analysis of the bending, torsion, and full load braking strength of the vehicle body, the maximum von-Mises stress was lower than the material yield strength by 2/3, which met the design requirements.
- The fatigue life analysis showed that the fatigue life of the designed vehicle body reached 6.5 × 10
^{8}km when driven on a general asphalt road at a speed of 18 km/h. When rotating or plowing at a speed of 2 km/h, the fatigue life reached 11,190 km and 23,166 km, respectively. - This research completed the development and fabrication of a small electric tractor, which met the requirements of manual driving and automatic driving. In addition, the tractor was equipped with two 7.5 kW induction motors, driven by lithium batteries, which can achieve at least 3.5 h of working time, and the rotary tillage operations can reach a depth of about 15 cm. The result of field tests on the prototype electric tractor are shown in Table 5, Table 6 and Table 7.

## Author Contributions

## Funding

## Institutional Review Board Statement

## Informed Consent Statement

## Acknowledgments

## Conflicts of Interest

## References

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**Figure 12.**Analysis of driving on a C-level road at = 2 km/h during rotary tillage operation. (

**a**) Von-Mises stress distribution; (

**b**) the von-Mises stress of the car body where σ

_{e,max}occurs; (

**c**) stress amplitude and number of average stress; and (

**d**) fe-safe life simulation.

**Figure 13.**Analysis of driving on D-class road surface at = 2 km/h during rotary tillage operation. (

**a**) Von-Mises stress distribution; (

**b**) the von-Mises stress of the car body where σ

_{e,max}occurs; (

**c**) stress amplitude and number of average stress; and (

**d**) fe-safe life simulation.

Vehicle Parameters | ||
---|---|---|

Length | Width | Height |

1720 mm | 1100 mm | 660 mm |

Tire size | Total vehicle weight | |

Front 26 × 8-14 | Rear 26 × 10-14 | 650 kg |

Type Parameter | SPFH 590 | STKM 11A |
---|---|---|

Density (kg/m^{3}) | 7850 | 7850 |

Young’s Modulus (MPa) | 210 | 210 |

Yielding Stress (MPa) | 420 | 175 |

Ultimate Stress (MPa) | 590 | 290 |

Poisson’s Ratio | 0.3 | 0.3 |

Front Suspension | Rear Suspension | |
---|---|---|

Spring Constant (N/mm) | 27.5 (Kf) | 27.5 (Kr) |

Damping Coefficient (N.s/mm) | 0.96 (Cf) | 2.16 (Cr) |

Rated Voltage | DC72V |
---|---|

Rated power | 7.5 kW |

Instantaneous peak | 17.8 kW |

Maximum speed | 5800 rpm |

Maximum torque | 23.2 N-m |

Field Test | |||
---|---|---|---|

Velocity (km/h) | Road Type | Current (A) | Power (W) |

3.05 | Asphalt | 2.38 | 185.64 |

Hard | 7.3 | 569.4 | |

Soft | 3.83 | 298.74 | |

Grass | 2.5 | 195 | |

1.02 | Asphalt | 14.16 | 1104.48 |

Hard | 26.0 | 2028 | |

Soft | 10.85 | 846.3 | |

Grass | 16.7 | 1302.6 |

Velocity (km/h) | Depth (cm) | Driving Current | Tillage Current | ||
---|---|---|---|---|---|

Current (A) | Power (W) | Current (A) | Power (W) | ||

1.02 | 5 | 10.9 | 850.2 | 28.1 | 2191.8 |

10 | 7.9 | 616.2 | 32.8 | 2558.4 | |

15 | 12.9 | 1006.2 | 37.4 | 2917.2 | |

3.05 | 5 | 25.7 | 2004.6 | 44.3 | 3455.4 |

10 | 28.2 | 2199.6 | 49.1 | 3829.8 | |

15 | 37.2 | 2901.6 | 52.2 | 4071.6 |

Drive Current and Tillage Current (A) | |
---|---|

Low speed 1.02 (km/h) | 50.3 A |

High speed 3.05 (km/h) | 126.6 A |

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**MDPI and ACS Style**

Chen, Y.-C.; Chen, L.-W.; Chang, M.-Y.
A Design of an Unmanned Electric Tractor Platform. *Agriculture* **2022**, *12*, 112.
https://doi.org/10.3390/agriculture12010112

**AMA Style**

Chen Y-C, Chen L-W, Chang M-Y.
A Design of an Unmanned Electric Tractor Platform. *Agriculture*. 2022; 12(1):112.
https://doi.org/10.3390/agriculture12010112

**Chicago/Turabian Style**

Chen, Yung-Chuan, Li-Wen Chen, and Ming-Yen Chang.
2022. "A Design of an Unmanned Electric Tractor Platform" *Agriculture* 12, no. 1: 112.
https://doi.org/10.3390/agriculture12010112