Design, development and field assessment of a controlled seed metering unit to be used in grain drills for direct seeding of wheat

A new controlled seed metering unit was designed and mounted on a common grain drill for direct seeding of wheat (DSW). It comprised the following main parts: (a) a variable-rate controlled direct current motor (DCM) as seed metering shaft driver, (b) two digital encoders for sensing the rotational speed of supplemental ground wheel (SGW) and seed metering shaft and (c) a control box to handle and process the data of the unit. According to the considered closed-loop control system, the designed control box regularly checked the revolution per minute (RPM) of seed metering shaft, as operation feedback, using its digital encoder output. The seeding rate was determined based on the calculated error signal and output signal of the digital encoder of the SGW. A field with four different levels of wheat stubble coverage (10%, 30%, 40% and 50%) was selected for evaluation of the fabricated seed metering unit (FSMU). The dynamic tests were conducted to compare the performance of installed FSMU on the grain drill and equipped grain drill with common seed metering unit (CSMU) at three forward speeds of 4, 6 and 8 (Km/h) for DSW. Results of the FSMU assessment demonstrated that an increase in forward speed of grain drill (FSGD) and stubble coverage did not significantly affect the seeding rate in the grain drill for DSW. Using the FSMU reduced the coefficient of variation (CV) by approximately 50%. Consequently, applying the FSMU on the common grain drill led to a desirable seeding rate at different forward speeds of the grain drill and stubble existence.