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Unformatted text preview: Year 2010 Month 10 Day 17 UAV Servo Control Experiment Aerospace Engineering Laboratory II Name : Martin Suhartono Student ID : 20106182 Martin Suhartono - 20106182 Page 2 1. Objective a. To practice the students in receiving error signals from a potentiometer b. To practice on the location control of the control-type Direct Current (DC) motor using the error signals c. To understand the use of pulse width modulation (PWM) signals to control the servo motor as well as its characteristic 2. Introduction A servo basically is an automatic device that utilizes the error-sensing feedback to correct the performance of a mechanism. A servo motor is then a specialized actuator that has the capability to sense a feedback (or a signal) and, subsequently adjust the performance of the mechanism to match the desired action. A servo motor usually consists of a DC electric motor, potentiometer and the control circuit. The DC electric motor functions to convert the electrical energy into kinetic energy useful in performing the desired action. On the other hand, the potentiometer functions to detect the rotation angle of the main shaft while the control circuit generally controls the rotation angle of the servo motor. A servo motor in general operates based on the principle of negative feedback. When the pulse-width modulation (PWM) signal is sent to the servo motor, it is translated to position command by the electronics inside the servo. The motor is then powered to generate potential difference driving the potentiometer to rotate until it reaches the corresponding value that will neutralize the potential difference. Servos are controlled by sending them a pulse of variable width. This pulse has minimum, maximum values and repetition rate. Given the constraint on the rotational ability of the servo, the neutral point is usually designated at the 45 degree rotation, where the amount of potential rotation in clockwise direction is equal to that in anti-clockwise direction. This rotation angle is commonly corresponding to the signal duration of 1.5 ms. The angle of rotation is then controlled by the duration of the pulse applied to the control wire. This is called as the pulse width modulation signal mentioned above. For example, 1.0 ms PWM usually sets the rotation angle to 0 degree while 2.0 ms PWM sets it to 90 degree. The period from one signal to another is usually between 14-25 ms and it makes up one cycle. The ration between the cycle duration to the duration of PWM is called the duty cycle. For the first part of this experiment, we will see the potential difference (error voltage) between the outputs of two potentiometers: the input potentiometer and output potentiometer. The magnitude of this potential difference is actually proportional to the difference in their angles of rotation. This potential difference, in a closed circuit, will be amplified and is used to move the motor to match the desired action. Hence the motor will keep on rotating the potentiometer until the error voltage becomes 0, which means Martin Suhartono - 20106182...
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This note was uploaded on 03/19/2012 for the course AEROSPACE MAE309 taught by Professor Kwonsejin&hyunchulshim during the Spring '12 term at Korea Advanced Institute of Science and Technology.
- Spring '12