Aerospace & Defense Technology - October 2022 - 6

Robotics & Unmanned Systems
dedicated to identifying components
that operate at -180°C and tolerate
125°C. Specific families of electronic
components demonstrate normal functionality
at cryogenic temperatures and
allow for integrated systems to meet the
functional needs of operating in Permanently
Shadowed Regions (PSRs), Mars
polar sites, or deep space ocean worlds
such as Europa or Enceladus without
the reliance upon survival heating. This
" built-in resilience " yields savings in
power and mass attributed to thermal
management systems. Motiv has taken
the approach of design for the environment
to the extremes by qualifying
hardware to sustain and operate through
these harsh environments at the core
technology level. The design objectives
also include utilizing 100 krad components
throughout.
The capabilities of the DEEDS controlsection
are significant, with a
ler
28V-120V wide operating input bus voltage
range. These voltages span typical
spacecraft operational ranges for both
robotic and human exploration critical
systems. Total current production reaches
up to 20A and approaches 2.5 kW of
Bulk Metallic Glass Coupon (Courtesy
of Amorphology)
output power. Dual brake controls
exist for either power-off systems,
which require pull-in capabilities
for operation, or power-on
brakes used to energize
restraint systems when utilized
in systems that require
active braking, such as
human-driven rovers. The
controller is also outfitted
with dual resolver sensing for
fine resolution when operations
dictate fine positioning
or velocity controls.
Finally,
the controller supports a variety
of commutation schemes as
required by the operation serviced.
Operational modes include a
closed-loop control schema for velocity
and position control. For specific
torque control dominated operations,
both current control and utilization of
locally derived actuator torque sensing
are available. The controller also supports
motion profiling to execute various
user-defined operations.
Bulk Metallic Glass
In addition to the cryogenic avionic
operations, Motiv is leveraging the
emergence of Bulk Metallic Glass (BMG)
in the construction of the geared torque
production system. The actuation system
is a scalable, modular component
that allows for multiple stages
of planetary gearing, a power-off
brake (typical for robotic operations),
a power-on brake (equivalent
to the brake pedal in a
vehicle), fine resolution
output resolver
sens ing ,
and a
cryogenic brushless
DC motor.
This can be adjusted
to meet specific
output torque production
needs as required by
varied user applications.
Recent developments in BMG
materials used in planetary gear
systems have shown excellent wear
properties with specific alloys. Not
only does the material wear well with
minimal galling, but gears have been
operated cryogenically without the need
for lubricants. Demonstrating long-life
6
mobilityengineeringtech.com
LTV Wheel
(0.8m Dia.)
with DEEDS
Actuation
Hub Drive
operations, down to -180°C, through
dozens of deep thermal cycles, consistent
with a lunar rover mission of 5+
years, is a game-changing achievement.
While configurable to a multitude of
operational cases and configurations, the
initial DEEDS specification was based
upon a popular " corner case " promoted
by NASA's LTV definition. The LTV specification
is desirous of a 500 kg rover
with a 500 kg payload capacity, >10
kmph traverse, and capabilities for cornering
and driving up and down inclines.
The extrapolated requirements established
the electrical and mechanical
requirements for an LTV wheel system
supported by the DEEDS architecture.
Testing
Testing the DEEDS system will include
a wide range of validation activities. A
lifetime test program cycled through
temperature extremes will exercise the
actuation output to an equivalent set of
revolutions to yield a minimum of 50
km and a goal of 250 km. Dynamometer
testing at various thermal setpoints
will also evaluate cross-moment loading
capabilities and peak torque performance
consistent with simulated lunar
incline and cornering traverse models,
as well as expectations for releasing
from embedment conditions. Lastly,
regolith incursion testing using simulants
will be exercised to validate dust
Aerospace & Defense Technology, October 2022
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Aerospace & Defense Technology - October 2022

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