IEEE Robotics & Automation Magazine - September 2022 - 17

We selected TRACO Power dc-dc converters for the different
stages because they are efficient and reliable components that
provide galvanic insulation between the primary and secondary
lines. The current deliverable by each dc-dc converter is
sized according to the power budget, and the output is further
protected with fuses.
In the case of ExoTeR, the PCDE is a rather simple design
with little intelligence onboard and limited to the functions
just described. In MaRTA, we decided to add a microcontroller
within the PCDE board to control certain additional
functionalities and provide more useful data. The battery status
is displayed on an LCD screen at the back of the rover.
Similarly, the consumption of several power lines is monitored,
including the total power currently running the rover.
The current measurements of the PCDE can be helpful
to find potential issues and degradation in the electronics. A
colored LED alerts the operator when the battery is low and
needs to be replaced. An emergency stop function is also
implemented within the PCDE that can accept emergency
signals coming from three sources: a physical push button at
the deck of the rover, similar remote emergency switch that
communicates with the rover PCDE through a radio link, or
specific telecommand message sent from the rover OBC to
the PCDE. Regardless of the source, an incoming emergency
signal effects cutting the power to all motors in the platform
and stopping any active motion, yet the rest of the
avionics and logic power to the MCE are maintained to
allow for potential recovery actions and proceed with any
test execution.
OBC and Sensor Integration
Here, we address the topic of integrating the elements that are
most relevant to our actual robotics field. These are the OBC
and sensors used by the rover that are the source of the data
needed for implementing many important functionalities.
Looking at the proprioceptive type of sensors, relevant
examples would be accelerometers, gyroscopes, or full threeaxis
inertial measurement units (IMUs). Also worth mentioning
within this group are the motor encoders and other
sensors that belong to the control of the mobility system,
which were properly addressed in the " Mechanical Design "
section. A sensor present in all of our lab rover prototypes is
the Sensonor STIM-300 IMU, a small-footprint sensor with
three-axis gyros and accelerometers that uses microelectromechanical
system (MEMS) technology to provide 3D orientation
data. Other sensors we have opted to mount on
MaRTA are the Level Developments SOLAR dual-axis inclinometer
or the KVH DSP1760 Fiber Optic Gyroscope,
which, together, can provide full rover attitude estimation by
tracking the gravity vector and rover azimuth, respectively.
As for the exteroceptive sensors, the most widely used
ones would be cameras, and, within this type, certainly, the
optical sensor cameras [red, green, blue (RGB) or monochrome]
are the most relevant due to their low cost, miniature
size, ease of integration, and heritage as well as in terms
of the algorithms available for image data processing.
Similarly, stereo camera rigs are commonly used to provide
depth information. Depth data are essential for any navigation
application since it forms the basis for two key functionalities,
localization and mapping. The relevance of stereo
cameras is highlighted in space robotics applications, given
the existence of space-grade sensors of this kind.
This is why both ExoTeR and MaRTA are equipped with
several stereo cameras (the FLIR Bumblebee BB2 and XB3),
typically one dedicated to localization mounted at the rover
body rim pointing downward and close to the ground, and
another one for mapping and navigation mounted on top of a
mast with pan-tilt pointing capability from a higher-perspective
viewpoint. Other exteroceptive sensors, such as depth
cameras (RGB-Depth cameras), time-of-flight cameras, and
laser sensors or lidars, have been used in our lab for some
dedicated tests; however, we do try to limit their use in our
applications and research activities due to the lack of existing
space-qualified sensors of this type.
While we try to be representative in the types of sensors
we use, it is important to note that we do not use space-grade
or qualified components in this regard, which would make
our research unaffordable. Similarly, when it comes to choosing
the OBC, we opt for embedded computers used in a wide
range of robotics applications. Trying to be representative of a
space-grade processing module would require working with
an expensive and considerably complex LEON4 architecture,
with the accompanying limitations on software developments
and prototyping activities.
The first computer in ExoTeR was selected from the
PC104 form factor due to its flexibility and modularity as well
as the ability to customize the computer stack and interface
ports by selecting and adding specific layers, such as FireWire,
CAN bus, or Wi-Fi modules. However, the stack soon
became quite bulky, and the availability of processors was limited
to slightly old and low-power units. Therefore, at the
point of selecting the OBC for MaRTA, we decided to unify
and upgrade the OBCs in both rovers with embedded systems
from the Pico-ITX form factor. At the moment, both
rovers have almost identical OBCs, which is obviously a convenience,
carrying relatively new and powerful Intel processors
within a 64-b x86 system architecture.
Communications between processing modules in space is
typically done through point-to-point SpaceWire interface
links, and wireless communications use ultrahigh frequency
antennas and implement protocols for satellite communications.
In our case, these are replaced by Ethernet and
Wi-Fi standard communications for convenience of use in
a lab environment.
Human-Machine Interface, Thermal,
and EMI Considerations
The electrical design of the rover is completed taking into
consideration other aspects at the system level. One of them is
related to grounding and harness routing to minimize the
EMI as much as possible. We followed well-known recommended
practices for limiting the EMI and protecting
SEPTEMBER 2022 * IEEE ROBOTICS & AUTOMATION MAGAZINE *
17
IEEE Robotics & Automation Magazine - September 2022

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