Autonomous Helicopter

The Biorobotics laboratory runs an active autonomous helicopter project, which commenced in January 2000. The aim of the project is to achieve visually mediated hover and forward flight without the use of GPS. The current aircraft is a Hirobo Eagle "X", a '60 sized, alcohol and nitromethane powered helicopter with many structural elements composed of carbon fibre to save weight. The dry weight of the airframe is 5kg.

The aircraft carries a sensor payload consisting of a custom made inertial measurement unit, a 3 axis magnetometer, a data concentrator/conditioner flight computer, a telemetry transmitter, and a video transmitter. Recently a GPS has been added to allow reconstruction of flight trajectories. The entire package weighs more than 1.5kg at present. The next revision will wiegh less then 500g allowing the helicopter greater range and endurence, and more importantly, greater control authority.

All control and processing is performed on the ground. A standard remote control system is used to command the servos on board the helicopter. This approach allows us to concentrate on the specific sensing and control problems, with minimum time spent on packaging and embedding hardware and software.

Some of the disadvantages of this approach are occasional lost telemetry and video frames, and additional 20ms lag due to the processing inside the remote control transmitter. The major operational limitation is the limited range over which the system will function reliably (a few hundred metres).

As the capabilities of the helicopter increase, the incentive to produce a truly autonomous system will likewise increase.

Successes to date

First demonstration of autonomy 02/01/2001: Hover

A system was developed which allows the helicopter to hover while viewing three or more identifiable landmarks on the ground plane. The successful implementation showed that the control system design was esentially correct. Occasional oscillations are probably caused by variable phase lags in the remote control system.

Such a system by itself is not particularly useful, however a modified variant that could hover over a known pattern on a helipad may have some applications.

Second demonstration of autonomy 05/06/2001: Forward Flight

The simple visual system used in the hover test was replaced with a motion sensitive visual system that determines the apparent angular rate of of the ground plane in the longitudenal and lateral directions. Height is solved from the airspeed of the craft and measured optical flow.

The aircraft successfully flew for a distance of 2km under closed loop control. The only axis not controlled automatically was the roll axis, which was required to stop the aircraft wandering sideways into nearby swamp. To maintain a reliable telemetry distance, the pilot rode in the back of a utility (light truck) which pursued the helicopter at up to 70km/h.

The next task in this part of the project will be to close the roll loop, and to achieve a more reliable indicator of airspeed (which is a problem under the downwash from the rotor).