Effects of Quadrotor Motions on its Accelerometers: Theory and Simulation Results Vahid Khorani 1 , Alireza Mohammad Shahri 2 , S. Mohammad Reza Mirfakhar 1 , and Naeem Ajilforoushan 1 1 Mechatronics Research Laboratory (MRL), Islamic Azad University, Qazvin Branch, Iran 2 Electrical Engineering Department of Iran University of Science and Technolo- gy, IUST, Tehran, Iran. Abstract Quadrotors are Vertical Take-Off and Landing (VTOL) vehicles that use Iner- tial Measurement Units (IMUs) in the heart of their navigation and instrumenta- tion system. Usually IMUs with three accelerometers are used to calculate tilt an- gles and robot location for inertial navigation. In this paper it is shown that horizontal accelerometers used in IMU are not useful for tilt calculation and iner- tial localization of quadrotors. Results show that values measured by horizontal accelerometers are totally independent from earth gravity acceleration and cannot be used to calculate the tilt angles. Additionally these values are not related to the quadrotor linear accelerations relative to the earth-frame and should not be used in quadrotor inertial localization. 1 Introduction Quadrotors are an emerging rotorcraft concept for unmanned aerial vehicle (UAV) platforms. The vehicle consists of four rotors in total, with two pairs of counter- rotating, fixed-pitch blades located at the four corners of the aircraft (Hoffmann, Huang et al. 2007). A quadrotor which is under investigation and is implemented in Mechatronics Research Laboratory (MRL) is shown in Fig. 1. Having four ro- tors makes the quadrotor able to be controlled without using swash plates to change the pitch angle of the blades unlike the helicopters. This simplifies both the design and maintenance of the quadrotor. Using four rotors cause the quadrotor to be stable and carry more payloads compared to the other flying platforms. This makes the quadrotor a suitable platform for being used as an autonomous robot which can carry equipment like laser scanner, camera, on-board real-time PC, and etc.