In this study, a hydraulic arm was developed for the robotic cotton picker and integrated with the e-vehicle. The hydraulic arm had three degrees of freedom (DOFs), that moved in vertical, rotational, and radial motion. A roller-type end-effector was installed at the front of the arm that came close to the cotton boll and separated it from the plant. A vacuum unit was generating a suction pressure in the hose pipe, allowing it to suck up the picked cotton bolls and transport them into the storage tank. The hydraulic arm with e-vehicle was operated in the field for three different plant-to-plant spacing 250, 350, and 450 mm at suction pressures 25, 50, and 75 mmHg to assess its performance. The maximum picking efficiency and picking capacity were 92.79 %, and 567 bolls picked/h, respectively observed for plant-to-plant spacing of 450 mm at a suction pressure of 75 mmHg. The minimum damage of green bolls and losses of cotton bolls were 126 bolls/ha, and 3.79 %, respectively observed for plant-to-plant spacing 450 mm at a suction pressure of 75 mmHg. The minimum trash content was 20.50 g observed for plant-to-plant spacing 450 mm at a suction pressure of 25 mmHg. The most suitable combination for achieving the acceptable performance of a hydraulic arm integrated with an e-vehicle in a cotton crop was the plant-to-plant spacing of 450 mm and suction pressure of 75 mmHg.