Design and implementation of a hardware-in-the-loop simulation system for small-scale UAV helicopters q Guowei Cai, Ben M. Chen * , Tong H. Lee, Miaobo Dong Department of Electrical and Computer Engineering, National University of Singapore, Singapore 117576, Singapore article info Keywords: Hardware-in-the-loop simulation UAV Helicopter Flight control abstract We present in the paper the design of a hardware-in-the-loop simulation framework and its actual imple- mentation on our custom constructed unmanned-aerial-vehicle (UAV) helicopter systems. Real-time hardware-in-the-loop simulation is one of the most effective methods for the verification of the overall control performance and safety of the UAVs before conducting actual flight tests. In our proposed frame- work, four modules, which include onboard hardware, flight control, ground station and software, are integrated together to realize the hardware-in-the-loop simulation. This design is successfully utilized for simulating several flight tests including basic flight motions, full-envelope flight and multiple UAV formation flight. Results obtained show that the constructed hardware-in-the-loop simulation system is highly effective and useful. Ó 2009 Elsevier Ltd. All rights reserved. 1. Introduction Unmanned aerial vehicles (UAVs) have recently aroused great interest and attention in the academic circle worldwide because of their great potential in both military and civil applications. Many research groups have constructed their own UAV platforms for var- ious research purposes (see, for example [1,5,7,11–13]). Generally, the construction of UAVs is costly and time consuming. Safety is thus a primary issue that one is facing in conducting actual flight tests. As such, intensive testing and simulation, especially with the actual UAV hardware in the simulation loop, is an effective way to detect and prevent unnecessary malfunctions of hardware, software and automatic flight control systems. Hardware-in-the- loop simulation is a real-time simulation method or framework, in which the UAV platform is reacting the same way as it in the real experiment. Using such a method, researchers can effectively evaluate the reliability of the overall UAV system. In particular, the framework can be intensively used to examine the perfor- mance of designed automatic flight control algorithms. Necessary enhancements and modifications can then be done before actually testing the UAV system in the sky and thus the probability of test flight accidents can be greatly minimized. We have recently constructed two sets of small-scale UAV heli- copters, HeLion and SheLion, shown in Fig. 1, respectively. The UAVs are utilized for implementing newly developed automatic control techniques, and missions such as ground target detecting and tracking as well as multi-UAV cooperation. Both UAV helicop- ters are upgraded from radio-controlled hobby helicopter, Raptor 90, by equipping with a custom designed onboard avionics system [2] with a comprehensive onboard and ground station software system [6]. For the sake of safety and reliability evaluation, we pro- pose in this work a hardware-in-the-loop simulation framework for our UAV platforms by integrating the developed hardware and software systems together with the dynamic model of the UAV helicopter. This framework includes the following four mod- ules (1) onboard hardware module; (2) flight control module; (3) ground station module and (4) software module. Various hard- ware-in-the-loop experiments conducted show that the frame- work is effective and instrumental to real flight tests. For certain flight tests, the result of the hardware-in-the-loop simulation is able to provide safety alerts to human pilots in advance. As a result, the human pilot can overtake the automatic system and perform a timely manual control when the UAV helicopter become unstable. The outline of this paper is as follows: In Section 2, we present the complete design procedure of our proposed hardware-in-the- loop simulation framework. All of the modules in the framework will be introduced in detail. Several simulation results, including those for basic flight motions, full-envelope flight and formation flight, are illustrated in Section 3 to verify the proposed simulation framework. Finally, in Section 4, we draw some concluding remarks. 2. Design of hardware-in-the-loop simulation framework The framework of hardware-in-the-loop simulation is depicted in Fig. 2. This framework includes: (a) an onboard hardware 0957-4158/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.mechatronics.2009.06.001 q This work is supported in part by Defence Science and Technology Agency (DSTA) of Singapore under a Temasek Young Investigator Award. * Corresponding author. Tel.: +65 6516 2289; fax: +65 6779 1103. E-mail addresses: g0301341@nus.edu.sg (G. Cai), bmchen@nus.edu.sg (B.M. Chen), eleleeth@nus.edu.sg (T.H. Lee), eledm@nus.edu.sg (M. Dong). Mechatronics 19 (2009) 1057–1066 Contents lists available at ScienceDirect Mechatronics journal homepage: www.elsevier.com/locate/mechatronics