Development and performance assessment of a DC electric variable-rate controller for use on grain drills

Site-specific crop management is a technology that modulates the application rate of field inputs such as seeds, fertilizers, and herbicides based on the needs of each management zone within a field. There are two methods available for changing the seeding rate in fluted-feed-roll type seed drills: (1) changing the active feed-roll length and/or, (2) changing the seed meter drive shaft speed. A possible method to develop a variable-rate seeder is to add a controller to a conventional grain drill which can change the speed of the seed meter drive shaft on-the-go. This was explored in the present study with the following main objectives: (a) to design a DC electric variable-rate controller to change a grain drill from a uniform to a variable-rate seeder, and (b) to determine the response time of the system. A motor control circuit was designed which used the output signals of two encoders as feedback. The system was consisted of: (1) a DC motor with a fixed-ratio gearbox, (2) encoders for sensing the rotational speeds of the grain drill drive wheel and the motor, (3) a GPS receiver, (4) a pulse-with-modulation (PWM) DC motor controller, and (5) a laptop. Dynamic tests were conducted at application rates of 87.5 (low) and 262.5 (high) kg ha−1. Sigmoid equations were best fitted to the transition data from low-to-high and high-to-low seeding rates. Our findings showed that the response times of low-to-high and high-to-low transition rates were 7.4 and 5.2 s, respectively.