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The purpose of this study was to develop an automated manual transmission (AMT) of agricultural tractors using an electric actuator. A shuttle shifting actuator and a clutch actuator were developed to control a manual type shuttle gearbox and transmission. To evaluate performance of the AMT, the experimental test-bed was used. The test-bed was consisted of a powertrain of the agricultural tractor, an electric motor instead of a tractor engine, a three-phase inverter to control the motor speed, the actuators, and I/O interface modules. The actuators were installed at the link of the shuttle gearbox and transmission of the powertrain, respectively. The potentiometer signals of the actuators and the rotational speed of the input shaft of the motor and the transmission axle were measured and used to control the actuators. A PID simulation program was developed to optimize position control of the actuators. The AMT control algorithm was developed and experimental tests were conducted to evaluate the performance of the AMT at speed levels. The results showed that the actuators were controlled properly to achieve the maximum overshoot of less than 5%, the settling time of less than 1.5 s, and the steady-state error of less than 1% at all speed levels. The averaged total duration of all speed levels was less than 2.5 s and the speed of driving shaft reached the target speed within 3 s. The results showed that the developed shuttle shifting transmission control algorithm could be useful for the automated manual transmission (AMT) of agricultural tractors.