Figure 15. Mikrokopter-based quadrotor equipped with Gumstix and LRF [32]. assignment. As described in Figure 17, each quadrotor is equipped with an onboard controller to track input commands sent by the GCS that collects position and/or attitude data of the quadrotors from the Vicon motion capture system. Data from the onboard vision sensors are sent to the GCS using a dedicated communication link. Conclusions This article has presented eight quadrotor OSPs with descriptions of their avionics, sensor composition, analysis of attitude estimation and control algorithms, and comparison of additional features. Several research projects that use OSPs as a main flight controller are described. Figure 16. Three quadrotors in an experiment for an online task assignment algorithm. Among the eight OSPs summarized in this article, we have implemented five by utilizing the benefit of OSPs that allow to build own systems at a low cost with less effort. To bring out continued improvements based on communities' work, objective evaluations of OSPs remain an important open problem. The meaning of OSP had been more about software, but it is expanding to hardware and even products. There is already a project that has open hardware blueprints and a 3-D model of the quadrotor airframe that can be ordered from 3-D printing services. Sharing the same platform will become easier with such services. We expect that more OSPs for UAV will be initiated in the future. Vicon Motion Capture System Camera/Motion Capture Hardware Ground Control Station Communication Electronics Vicon Tracker Software Individual Quadrotors Controller PCTx PPM Generator Onboard Attitude Controller USB Frame Grabber 2.4 GHz Radio Transmitter 2.4 GHz Radio Receiver Operator User Interface 2.4 GHz Video Receiver 2.4 GHz Video Transmitter IMU Display Onboard Vision Sensor Command Figure 17. Overall hardware architecture of the indoor quadrotor flight system for Figure 16. Multiple layers indicate one for each quadrotor. 44 * IEEE ROBOTICS & AUTOMATION MAGAZINE * SEPTEMBER 2012