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A
well-defined design process transforms mere figments of the
imagination into major feats of engineering.
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''We're
continually looking for ways to streamline the design process,''
reports Will Myers, Director of Engineering at Zeus. Headquartered
in Northwest Arkansas, Zeus is a small, rapidly growing company
that has emerged as a leader in off-road vehicle design,
analysis and dynamics.
With a long history in design engineering, research and
development and new product development at such corporate
heavyweights as Lockheed Martin and Conoco, Myers has dedicated
countless hours to defining the design process for prototype
development.
Under his leadership, Zeus approaches each new project using
a proven process that relies on the managed, continuous evolvement
of a design through three distinct phases.
While the process itself is exacting
to eliminate unnecessary backtracking, it also provides
ample latitude for the exchange of ideas that drives innovation
in design.
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The Concept Design Phase
In the first phase, or concept design phase, Zeus uses very broad terms to describe
the basic concept for the design. How is this vehicle going to look? What
is the specification for the design?
''Based on the target market, established specs and research,
we gather as many design concepts as we can with no preconceived
notions about whether the ideas are good or bad. The only
limits are an engineer's imagination and creativity,'' says
Director of Design Joe Partain. ''Then we add only sufficient
detail to the concept to enable proper evaluation.''
The phase concludes with a selection of a single design
concept. Zeus performs top-level trade studies and analysis
related to structure, major components or key systems in
the design concept.
Preliminary in nature, the concept contains only minimal
detail when compared to the final design. Features included
are major load paths, major component locations and major
interfaces with adjoining systems and overall structure.
The Preliminary Design
Phase
The preliminary design phase starts with the concept design
and sees the evolvement of a detailed layout, which possesses
most of the detail contained in the final released drawings.
This includes all major structural and mechanical members,
systems, electrical and electronic components, fasteners
and interfacing components and systems.
The team performs additional analysis as required to size,
define and verify the design. With the exception of critical
or master location dimensions, the layout displays minimal
dimensions. Planning, scheduling and other related activities
also occur in this phase.
The Detail Design Phase
The detail design phase consists of preparation and release
of the final detail and assembly drawings, related specifications
and supporting documents for production. The team completes
and documents the required analysis to thoroughly substantiate
the design and also prepares and releases tool designs
for fabrication. Any associated planning and scheduling
updates take place during this time.
''Once the drawings are approved and released by the project
manager, we are ready to begin fabrication,'' explains Partain.
Technicians use the drawings directly to produce numerically
controlled machined parts and molds.
''In most cases, fabrication starts before the design process
is finished,'' he continues. ''This overlap decreases the
amount of time that elapses from the initiation of the project
to when the prototype is ready for testing.''
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Innovation
from the Inside Out
Zeus is under contract with the Office of Naval Research
and United States Marine Corps Vehicle Group to design and
to build an off-road Light-Strike Medical Evacuation Vehicle
(LS-MEV) from scratch.
The vehicle's required dimensions are 60 inches wide, 60.2
inches tall and 200 inches long, and transportability in
a V-22 Osprey or larger aircraft is requisite.
A product of Zeus's customary three-phase
design process, the resulting prototype demonstrates various
innovative technologies and design features that set new standards
for future combat vehicles.
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A
Differential Feature
Due to the vehicle's strict size requirements,
Zeus had to overcome some considerable design challenges
with regard to packaging and stability. For example,
engine placement between the front wheels virtually
would eliminate suspension travel because of the width
constraint.
Positioning the engine above the suspension, on
the other hand, would create a different set of issues,
including compromised visibility for the operator,
decreased vehicle stability and failure to stay within
the provided height limitation.
''Basically, what we're looking for is the compromise
that not only provides good suspension travel and
soft ride but also sufficient handling and stability
in off-road conditions,'' reveals Design Engineer
Hayden Barr. |
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To maintain a low center of gravity for stability and a
high approach angle for off-road driving, Zeus instead located
the engine as low as possible just aft of the front suspension,
which, in turn, affected the drivetrain and suspension packaging.
Therefore, the firm worked in conjunction with an outside
gearbox manufacturer to develop a proprietary, narrow-track,
offset input differential, which acts as a structural member
of the frame.
Novel yet cost-effective, the solution maximizes suspension
travel and protects drivetrain integrity.
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A
Turn for the Better
In another instance, the LS-MEV went from a two-wheel drive
to a four-wheel drive in exchange for the capability to make
exceptionally tight turns for a vehicle of such narrow track
width.
''They wanted a 20-ft. turning radius. This car is very
compact width-wise, and we couldn't get the wheels to turn
that sharply because they were hitting other components confined
to that area,'' Myers recounts.
''We ended up steering the rear wheels to achieve the specified
turning radius.''
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An
Airborne Approach
Attempting to reduce weight and to offset
the large g loading at gross weight, Zeus chose an
unconventional design approach to the LS-MEV frame
and body. While several concepts received consideration,
the design team ultimately selected a solution borrowed
heavily from the aircraft industry.
Modeled after the highly loaded structural beams and
frames in an aircraft fuselage, the vehicle's frame
and body likewise are constructed of 6061-T651 aluminum
alloy with selected welded joints designed to be used
in the as-welded condition.
Machined rather than molded or formed, the aluminum
structures are expensive yet proportionately lightweight
and strong. The frame assembly is comprised of bolted
sub-assemblies for facility of manufacturing and ease
of component replacement.
Additionally, most of the parts in the frame and body
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A
Simple Substitution
Assembly of the LS-MEV takes place
in a very simple fixture attached to the frame and
to the floor. The vehicle remained bolted in the
fixture until it could rest on its tires and wheels.
Zeus custom-designed the fixture to replace the more
costly tooling that is typical for prototype assembly.
''While rather unusual for a wheeled vehicle,''
Myers admits, ''the construction method is quite
efficient for its intended purpose.''
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Suspension
System of Disbelief
''Our client
wants a vehicle that handles well and can carry a large
payload, but the loading has a significant impact on
whether a vehicle handles well,'' remarks Design Engineer
Troy Canalichio, the developer of LS-MEV's ''smart
suspension'' system. ''The air suspension system allows
us to meet both requirements.''
Designed for high performance over extreme off-road
terrain, the suspension system incorporates two leading-edge
technologies, airbag suspension and magnetorheological
shocks.
With variable ride height, spring rate and damping
rate, the vehicle automatically adjusts to an optimum
suspension, regardless of payload or terrain, to
deliver a reliably stable handling characteristic
and consistent ride. |
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Furthermore, the suspension control arms are machined from
lightweight 6061-T651 aluminum alloy plate to reduce the
LS-MEV's unsprung mass.
''Most of the innovation is driven from within our company,''
states Barr. ''We want to build compact, off-road vehicles
with high performance. There is nothing in the spec about
maximizing suspension travel, which is imperative for any
off-road application. We meet the spec with our design, but
we also meet our internal goal to maximize suspension travel
for a comfortable ride.''
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Continuity
of Focus
''We usually have engineers assigned to specific systems,
including suspension, powertrain, steering, frame, styling…,''
Partain discloses. ''When you're thinking about a design
or looking for ways to build a better vehicle or improve
on a concept, it takes time. It just takes time and staying
on the problem.''
Barr and Canalichio are two of five design engineers who
are each responsible for several vehicle systems from initial
concept through the build process. The engineers design and
perform analysis on the system components that they ''own.''
They coordinate design space and load paths with their co-designers,
conduct vendor communications and purchasing, perform quality
inspections on received parts and collaborate with technicians
during assembly.
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Systematic
Steps to Success
According to Myers, the advantage of working in this manner
is that each engineer becomes the resident expert for a number
of designated specialties and is more cost-effective at making
quick, informed decisions regarding those vehicle systems
than any other individual in the company.
''You have to know at each step what you've got and what
it will do,'' he reasons. ''A seasoned engineer uses this
design process and does everything very systematically, one
step at a time. When you're finished, you don't have to guess
why it's not working. You'll just know that it will work.''
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Contact Will Harvey at info@gozeus.com or
479.439.6110, x111, to request additional information about specific
models. |
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