Conception of the aerial robot MARVIN for IARC
The basis of MARVIN is a usual model helicopter with a 23 cm3
two-stroke gasoline engine. It has a rotor diameter of 1.8 m
and an empty weight of 6.5 kg. Maximum payload is about 5 kg.
Figure 1 shows the structure of the MARVIN system, consisting
of the robot and the ground station. The following sections describe
some of the components in greater detail.
Figure 1: MARVIN system
The following sensor components are used onboard the robot and
in the ground station:
- GPS Receivers
A pair of GPS receivers, type RT-2 by NovAtel, Canada, serves
for determining the robot's position at a rate of 5 Hz and an
accuracy of 2 cm. One of the receivers is located onboard, the
other constitutes the reference point on ground. The whole system
is leant to IARC participants at no cost by the manufacturer.
- 2½D Compass
A collection of 3 magnetic field sensors (resonating fluxgates)
onboard measures the direction of the earth's magnetic field
relative to the helicopter. This allows the determination of
2 of 3 parameters of the robots orientation (rotation around
an axis parallel to the magnetic field vector cannot be
- Inertial Measurement Unit
3 semiconductor acceleration sensors measure the virtual acceleration
onboard, which consists of the gravity of the earth and the acceleration
in the robots movement. Because of this interference it is both
impossible to calculate the robot's orientation and the robot's
movement solely from the three measured values. This would involve
6 degrees of freedom.
3 piezo-electric rotation sensors measure the rotation rates
around all axes (yaw, pitch, roll).
The robot carries a digital photo camera with automatic exposure
control and a fixfocus wide-angle lens. This camera is used to
search, locate and classify the target objects with respect to
the competition task.
- Flame Sensor
A flame sensor enables MARVIN to detect fires, which may burn
within the competition arena and constitute a considerable thread
to the robot if approaching too close.
Between robot and ground station, two communication links are
- DECT Data Link
A pair of data communication modules based on the DECT standard
stemming from cordless telephones is used to perform all the
information exchange between the robot and the ground station.
The modules are manufactured by SIEMENS and constitute something
like a "wireless null modem cable" at 115 kbit/s bidirectionally.
Even the images of the digital photo camera are downlinked via
DECT. A specialized communication software is used that implements
a distributed shared memory view of the state parameters of the
overall system. Every piece of information is assigned a guaranteed
minimal fraction of the bandwidth available, which ascertains
real-time capability for the MARVIN software.
- Remote Control
A usual remote control unit for model helicopters is required
as a backup manual control and for test and development purposes.
One channel of the RC unit is used for switching between remote
and onboard computer control. If the onboard computer loses power,
control goes back to the human pilot in any case. After the human
pilot has enabled computer control, he continues steering the
robot until the onboard computer starts to produce servo control
signals on behalf of a software command.
The ground station consists of the followin components:
- GPS reference receiver
- DECT module for the digital data link
- a number of networked laptops running under Linux
The ground station runs the vision software for evaluating
the camera images from the robot and the "Mission Control"
software. The latter maintains a virtual map of the competition
arena and transmits intended flight courses to the robot. The
flight paths are planned according to an object list containing
intended photo positions and potential objects that should be
further investigated. An additional task of the ground station
is passing the GPS reference data from the ground receiver to
A single-board computer based on the SIEMENS SAB80C167 microcontroller
serves as MARVIN's onboard computer. This controller possesses
enough connectivity to interface all of the robot's hardware
components. It can handle lots of external signals and events
at very low CPU load - or even none at all. It's low power consumption
and sufficient computational power render it ideal for the tasks
The computer board has been designed and manufactured in the
MARVIN project course in cooperation with the board manufacturing
laboratory of the "Technische Fachhochschule Berlin"
Based on the GPS reference data and the onboard sensors, the
onboard computer is able to autonomously follow a given intended
course. The helicopter servos are driven directly by the controller.
A new "command" from the ground station is not required
as long as the intended course remains unchanged.