【正文】 ing a timer chip LM555 can provide an adjustable pulse duration ranging from ms to ms so as to test the heavyduty servomotor. Fig. 5 depicts a 555 timer for generating PWM pulses. The equations for the 555 timer are simple and easy to use. The equations (1) and (2) are shown as follows. （1） （2）Since Rs is variable, the time the signal is high will vary from to ms, the timing values are close enough to work with just about any servos. A 555 timer for generating PWM pulses.To verify the positioning control ability, both the conventional R/C servo and this designed heavyduty servo are tested with the mentioned 555 timer circuit. The output shaft of each tested motor is coupled with an individual angle indicator. If the PWM mand input terminal of both motors are connect together to a 555 PWM mand output, both motors will receive the same angle mand. A digital oscilloscope is used to monitor the pulse width of the PWM mand. The variable resistor of the PWM generator is adjusted gradually and the pulse width ranges from to ms, which can be monitored from the oscilloscope, and both motors rotate to the corresponding angle according to the pulse width of the PWM mand.On the other hand, proper pulse width was applied to test the response of the position feedback of different angles such as extreme left, extreme right and center position. It takes about seconds for the heavyduty servo to rotate from extreme left to centered position, longer than that of a conventional R/C servo, which is about seconds.IV. DiscussionIn the design of the motor and gearbox assembly, approximate diameter of output shaft must under carefully consideration since a potentiometer with an inner diameter is not an industrial standard ponent. In this experiment, the potentiometer with inner diameter is obtained by modifying an electronic variable resistor and the modification is not an easy work. For the purpose of mass production, this kind of potentiometers must be available from the market or must be specially designed. Although the circuitry can be achieved in many ways, we use a criterion of minimal ponent counts to design this prototype and results in an implementation of just two ponents, M51660L and L298.This prototype requires two voltages, 24V for the motor and 5V for the logic. For the simplicity of the power supply, a single power supply is considered. The motor rated voltage is higher than the logic supply in most circumstance such as 24 volts in this case. Therefore, the prototype was imbedded with a voltage regulator to regulate the motor rated voltage to logic 5 volts. Regarding the step response, a 90 degrees step mand was issued and the motor rotate to its required position with minimal overshoot. The proposed driver has a longer rise time, seconds, in parison with a conventional R/C servo since its higher reduction rate design in gearbox. However, this drawback can be solved when a faster response DC motor is adopted or a more sophisticated control algorithm, such as proportional and derivative (PD), is adopted in the design of the servo control loop.V. ConclusionIn this paper, we present a heavyduty servomotor for robotic applications. Because the driving capacity of the output Hbridge is up to 4 amperes, an industrial DC motor with a higher winding current and higher torque can be incorporated with this driver and serves as a powerful driving device in agricultural as well as industrial automation. Additionally, since the proposed servomotor is equipped with the wearresisting gear trains, it is durable than conventional R/C servomotor when used in heavy load circumstances. Testing on positioning accuracy was also conducted。附錄一A Heavy Duty Servo Motor Design in Robot ApplicationsChiSheng Chen 2 , TonTai Pan 1, 2 , Huihua Kenny Chiang 1 , PingLin Fan2, JoeAir Jiang31. Institute of Biomedical Engineering, National YangMing University, Taipei, Taiwan2. Department of Electrical Engineering, KuangWu Institute of Technology, Taipei, Taiwan3. Department of Bioindustrial Mechatronics Engineering, National Taiwan University, Taipei, TaiwanAbstractThis paper presents a design procedure of a heavyduty servomotor for robot applications. The conventional remote control (R/C) servo is an ingenious device that allows remote, proportional actuation of mechanisms by the simple movement of a lever of a robot. Because of the control of a conventional R/C servomotor is easy and the cost of it is less expensive, the R/C servos are used in widespread areas. However, an R/C servomotor outputs less torque than required in many applications such as robots design and high torque requirement for remote control cars or planes. Thus, a motor with high torque, which is easy to control, is favorable. In this paper, a DC gear motor is used as the controlled motor and a potentiometer was attached on the output shaft as a position feedback sensor. The proposed heavy duty R/C servomotor was tested with a monostable multivibrator, which generates to ms pulse width modulation (PWM) signals to drive the motor. Results of this study demonstrate that a heavy duty R/C servomotor can provide more torque in robot application than the mercial R/C servomotors.Keywords: Remote control motor, pulse width modulation, heavy duty, servomotor.I. IntroductionIn robot control applications, designers usually select either DC servomotor or brushless servomotor as the actuator to drive each joint. Both kinds of servomotors are expensive because the plexity of the driver system. Moreover, several servomotors are needed in a multijoints robot design and will make the designed robot too expensive to practical usage. The R/C servo is a selfcontained rotational positioning assembly originally designed to control an R/C aircraft or boat. The R/C servo is made up of a DC motor, Proceedings of International Symposium on Automation and Mechatronics of Agricultural and Bioproduction S