Fig. 1: The Autonomous Helicopter.
The Autonomous Helicopter Testbed (AHT) is a robotic platform for technology development and testing. The AHT is based upon the Bergen Industrial Helicopter, an RC model helicopter with a two-meter-diameter main rotor, powered by a twin-cylinder gas engine and a payload capability of approximately 9 kg. It is capable of completely autonomous flight, including GPS waypoint following and vision-based landing in hazardous terrain.
All sensing and computing is performed onboard. The computing stack uses the PC/104-based computer architecture and is composed of numerous cards, including a 700 MHz PIII CPU card, a Timer/Counter & DIO card, a 4-port serial card, an NTSC framegrabber card and a PCMCIA carrier card holding an 802.11b wireless LAN card. Sensors include a DGPS receiver with 2 CEP accuracy, a downward-looking 640x480 grayscale CCD camera, a downward-looking laser altimeter, an IMU, and a compass/inclinometer.
Power is provided by two lithium-ion laptop batteries fed into a 75-watt DC/DC PC/104 power-conversion board supplying +5V and +/- 12V to all onboard electronics. A laptop is used to run a GUI, which is used to send user-generated commands to, and display telemetry from, the AHT. This is achieved using an 802.11b wireless router connected to the laptop. In addition, differential corrections are sent to the DGPS receiver onboard the AHT via this same wireless link via a DGPS base station connected to a serial port on the laptop.
The QNX real-time operating system runs on both the laptop and AHT. Software development is done in C/C++. The AHT control system uses a behavior-based control architecture, and state estimation is achieved using an indirect Extended Kalman filter.
Milestones for the JPL AHT include the following:
To date, the JPL AHT has supported planetary-landing-related technology tasks, including the "Autonomous Vision Guided Safe and Precise Landing" and "Spacecraft Pinpoint Landing" tasks.
