The IntelliFly Helicopter
George Chronis
This project is a fully functional
autonomous helicopter. It was made to serve as an unmanned flying platform for
further development of different projects, like video probes, mail delivery to
different floors without elevators etc. The IntelliFly can be launched from
any place to any direction in the wind and successfully locate a preprogrammed
location in cartesian coordinates, relative to the point of take-off, and land
there. The helicopter is able to make real-time calculations about wind speed,
landing location, static or dynamic obstacles, power level, orientation,
altitude, etc. and perform successfull landings.
The IntelliFly is modeled on Kyosho's HyperFly platform, which is a radio
controlled electric small scale helicopter. It has a total length of 85 cm, a
rotor diameter of 70 cm, it weighs 700 gr with the battery and it is powered
by a LeMans AP29 electric motor. The helicopter does not have a tail rotor,
but a plate to stabilize the tail. Thus, although it is a helicopter, it is
controlled like an airplane, using two degrees of freedom: elevation and
turning. Without a tail rotor the helicopter cannot hover, but hovering may be
simulated using a head wind.
On the control side, two Basic Stamp II microcontrollers are responsible for
reading the sensors and issuing commands to the helicopter sevos. One servo
controls elevation and speed by moving the rotor at an angle relative to the
front to back axis of the helicopter, and another servo controls banking by
moving the rotor at an angle relative to the left to right axis of the
helicopter. Sensors of the IntelliFly include a gyroscope for flight
stabilization, an electronic compass that provides heading information, a
sonar sensor for altitude measurement, another three sonar sensors for
obstacle detection, a bump switch for shutting down the motor when landing, a
battery level sensor, and a custom-made detector that gives absolute speed
estimates.
The control algorithm is behavior based, similar to Brooks' subsumption
architecture. Each behavior, however, is assigned a weight that dynamically
moves it to different levels on the subsumption architecture based on sensory
input. For example, the power-monitor behavior is responsible for bringing the
helicopter to a safe land before the battery power is out, reagrdless of the
landing coordinates. Thus, it always issues commands that direct the
IntelliFly to decrease its altitude, and turn into the wind for a safer
landing. This behavior is suppressed when the battery level is high, but as
the battery level runs low the behavior is given is a larger weight, bringing
it to a lower (reactive) level in the subsumption architecture. There is a
function that continuously assigns weights to the behaviors, depending on the
sensory input.
The IntelliFly can successfully land to the specified coordinates 95% of the
time with an error of +- 2 m (.15%) from the helicopter's center of gravity to
the specified point. An average flight lasts about 1 min and 45 secs, and the
average distance travelled is about 1,300 m. The IntelliFly may fly at
absolute speeds of up to 50 km/h (relative speed depends on wind conditions).
The total flight time does not exceed 2 mins and 45 secs, due to battery life
constraints.