Customer Solutions

Using CompactRIO to Develop a Rotocraft Unmanned Air Vehicle

Author(s):

Roberto Pretolani, University of Bologna, School of Engineering; G.M. Saggiani, University of Bologna, School of Engineering; B. Teodorani, University of Bologna, School of Engineering; null null, null

Industry:

Aerospace/Avionics, Research, University/Education

Product:

CompactRIO, LabVIEW

The Challenge:

Developing a helicopter platform capable of autonomous flight to be used for control and navigation research in a university setting.

The Solution:

Programming a complete control system using National Instruments LabVIEW and CompactRIO as the flight computer to manage flight data acquisition and control the helicopter.

Engineering students are using model helicopters equiped with CompactRIO in autonomous flight research.

At the University of Bologna (UNIBO) DIEM Aerospace Department, we have developed a rotocraft unmanned air vehicle (UAV) for use as a test bed for researching UAV control and navigation.

The increasing interest in military UAVs is fueling an ambitious build-up in the private sector. It is well-known that UAVs represent a promising and cost-effective alternative to manned aircraft for many civilian applications. Compared to traditional air vehicles, UAVs offer significant advantages in terms of human safety (especially in dull, dirty, and dangerous missions), operational cost reduction, and work rate efficiency.

UAV and rotary wing UAV (RWUAV) system research is very advanced in the United States, but interest in Europe has begun only in recent years. As a result, the European Union has sponsored CAPECON, a UAV development program designed to kick-start a civilian UAV industry in Europe. At UNIBO, having recently carried out several research projects focused on developing and manufacturing fixed-wing UAV systems for the civil aviation market, we were eager to participate in the CAPECON program.

In addition, UNIBO has started a RWUAV research program, recognizing RWUAV systems as an alternative to fixed-wing UAVs for many civil applications due to their versatile flight modes, maneuverability, and vertical take-off and landing capability. The main goal of our RWUAV research program is to develop a helicopter capable of autonomous flight to be used for control and navigational research.

Hardware and System Architecture

We have built two model helicopter platforms, each with 5.5 kg payload capacity. Autonomous flying vehicles require avionics systems that let them maintain a stable altitude and follow desired trajectories. Such an avionics package consists of sensors, a computer, and data-link hardware as well as software to guide, navigate, and control the vehicle. These components are particularly critical for helicopters, which are well-known to be inherently unstable systems. For this reason, we decided to use National Instruments CompactRIO.

We have modified the Hirobo 60 and Graupner 90 hobby helicopters to accommodate the avionics hardware. NI CompactRIO works as the flight computer, and CompactRIO FPGA modules acquire sensor information and generate PWM actuator signals based on the control algorithms. CompactRIO Real-Time controllers receive sensor information from the FPGA and record all flight data, also managing wireless Ethernet communications with the ground control station. The CompactRIO FPGA receives and sends PWM actuators signals through the NI cRIO-9411 digital input module and the NI cRIO-9474 digital output module, respectively. The system acquires status parameters such as battery voltage by means of the NI cRIO-9201 analog input module.

The entire system weighs about 5 kg – well within the payload capability of the small-scale helicopters available to us. If bigger helicopter platforms become available, one or more NI CompactRIO modules could also act as backup and safety systems for the UAV.

Software

The RWUAV system has the typical CompactRIO application design architecture. The FPGA code uses four different timed read/write loops and one PID control loop for helicopter altitude control. The PID loop is closed at 50 Hz, and the write loops send PWM commands to the helicopter servo actuators and to the stabilized camera mount actuators. The first read loop acquires helicopter altitudes, angular rates, velocities, and GPS position from the Crossbow NAV420, which uses the RS232 protocol. The RS232 protocol is managed using FPGA digital input to guarantee deterministic data acquisition, which could not be achieved using a real-time application.

We use National Instruments LabVIEW Real-Time software for FPGA data acquisition, embedded flight data logging, and wireless Ethernet communication with the ground control station, managing ground control station communication with the NI LabVIEW Real-Time Communication Wizard. We developed the ground control station software in LabVIEW for Windows, and we run it on a laptop computer using Windows XP. The remote graphical user interface consists of two windows – the vertical cockpit window and the telemetry window – for real-time display of flight data information.

Conclusion and Outlook

With the help of National Instruments hardware and software, UNIBO laboratories is successfully developing a RWUAV as an integrated, reconfigurable system for researching control and navigation laws in rotary wing and fixed-wing UAV concept development. We performed the first flight campaign to test onboard sensor data acquisition and PID altitude control systems in hovering conditions. CompactRIO proved to be an easy-to-use, programmable tool that was reliable enough for helicopter control. In the near future, we plan to implement additional sensors (such as sonar altimeters) into the avionics package, to perform flight testing for more advanced maneuvers, and to implement navigation algorithms to build up a fully autonomous rotary wing system.

For more information, contact:

Roberto Pretolani

Department of Aerospace Engineering, University of Bologna, School of Engineering

Tel.: 39-0543-786932

Fax: 39-0543-786940

E-mail: pretolani@ingfo.unibo.it