Quad copter drone usually uses Brushless Direct Current (BLDC) motor as rotor due to high efficiency and small volume. The BLDC motor speed control is very important for drone position and velocity determent. The optical sensor can be used to measure the rotation speed of BLDC motor when tested in the laboratory. The calculation of rotation speed, use of Pulse Width Modulation (PWM) technique for speed control and serial interface can be implemented using a microcontroller. The purpose of this research is to control the speed of BLDC motor for ground test of drone rotor. From the measurements, the relation between speed reference signal controlled by PWM and actual speed are not linear due to time constant and fan load. The increase of PWM duty cycle produces the increase of motor speed. The regulating characteristics of motor can be used for speed control correction.

The purpose of this research was to test the measurement performance especially the measurement repeatability of tipping bucket rain gauge by varying the water intensities. Water intensities were obtained by converting water (volume) flow rates that enter to the section or mouth area of the rain gauge. The study was conducted using an experiment method. The result showed that by changing the water flow rate between 24–100 ml/min three times, the water volume in the tipping bucket were (18.93±0.60), (17.89±0.92) and (17.80±0.60) ml/tip respectively.