TURN Platform Ready for Final Assembly
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Thursday, January 26th, 2023
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Another TURN Patent Issued
The USPTO awarded another patent for the Tethered Uni-Rotor Network (TURN).
We already have patents protecting its physical embodiment, hover operation,
waypoint controls navigation, and takeoff and landing procedure; and have
several trade secrets for the attitude estimation algorithms and inner-loop
control laws. While this latest patent is a departure from the intended
physical embodiment, it provides an important legal feature that needed to
be addressed regarding alternative embodiments.
Currently, the existing patents address the optimal way the TURN system should
be implemented. The idea is that once TURN becomes operational other groups will
want to infringe on our intellectual property. If they are currently blocked by
the existing patents, could these technology imitators find an alternative
version of TURN (even a suboptimal embodiment) which gets around the IP we have
in hand, but still outperforms standard fixed-wing and VTOL systems.
This latest patent covers an embodiment that is a little bit out-of-the-box
(even for the TURN system), where it showcased a version which does not use a
central hub. Rather than the familiar hub and spoke arrangement, each of the
multiple wings are tethered directly to their closest neighbor. Again, this is
not the intended design, because without a central hub there is no good place
for a payload. However, this “non central hub” version still places wings under
tension and could significantly outperform more traditional drone solutions.
So, this patent makes sure that other groups cannot pursue the “second best”
TURN embodiment.
This alternative embodiment also solidifies the IP for the primary patents.
Most prior art describing tethered systems focused on lifting external cargo
or retrofitting fixed-wing aircraft for VTOL applications. But none described
system rotation placing a wing under tension as a key design element for
aerodynamic efficiency. So, the nominal pushback from the USPTO all focused on
prior art with aircraft spinning around a central point. This recently issued
patent debunks that notion because it shows that the central hub is not an
essential component to implement the TURN design methodology.
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Expediting Development with Bambu Lab 3D Printer
Devorto's primary objective is to develop the solar-powered High-Altitude
Platform Station (HAPS) TURN system as quickly as possible. Reaching that
goal consists of commercializing smaller platforms which pave the way
towards larger systems, thereby advancing both the business and the
technology in parallel. To that end, our immediate objective will
commercialize a Group 2 TURN platform, which weighs less than 55 pounds
and offers 20X the flight endurance of comparable multirotors currently
on the market.
We are currently building an outdoor flight demonstrator, which takes
the medium-level detail design, and progresses it to the final production
design stage. The design mostly leverages COTS components, but still calls
for a handful of custom brackets to join everything together. To iterate
quickly through various designs and to put a minimum viable product (MVP)
in the hands of beta-testing customers, Devorto is using 3D printed parts
to expedite the development process.
Devorto recently purchased a Bamboo Lab X-1 Carbon printer, which is far
superior to any printer previously encountered, because it was purpose
built to handle engineering grade materials. The calibration routine
includes build plate dynamic response testing and a LIDAR sensor which
scans for first layer defects. The print head is extremely lightweight
so it travels 2X-3X times faster than other machines on the market. This
means less time for parts to cool which produces better layer adhesion,
and allows half the standard layer height which leads to stronger more
homogeneous material properties.
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With this capable machine in hand, Devorto will use ASA for the material,
which has similar mechanical properties to ABS (the plastic used in Lego
blocks), but is 30% lighter and 10X more weather/UV resistant (ideal for
an outdoor drone application). After a month of using this printer on a
daily basis, the ASA parts are coming out in pristine condition with no
warping or layer line defects, and the printer proved itself to be an
indispensable development tool.
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Spiral Development
Wins Again
Spiral development has always been a core philosophy within the Tethered
Uni-Rotor Network (TURN) development plan. And working with smaller scale
platforms to identify unknown-unknowns before progressing to larger prototypes
has already proved immensely valuable. During the R&D phase of TURN’s
development, it provided insights on the nonlinear dynamics which influence
the controls laws, and it showcased a deficiency with conventional Attitude
Heading and Reference System (AHRS) algorithms providing the roll/pitch/yaw
state estimates for a rotating system. As Devorto progresses through our current
hardware milestone, spiral development worked its magic once again.
Our philosophy is to test everything early on. Before assembling all the
components needed for the outdoor demonstrator, we started with structural
load testing. Plastic injection molding the custom brackets is the desired
process for the commercial product, but 3D printing is much faster and
economical for the initial demonstrator. The downside with 3D printing, is
that Finite Element Analysis (FEA) models do not always match physical reality.
Materials within simulations are presumed to be homogeneous, which means they
have the same properties in all directions. But with printed parts, layer lines
must be considered as a potential failure source. As anticipated, load tests
showed a departure from the FEA models, where simulations pointed to the anchor
pin hole as the weakest point within a particular bracket, but through testing
we determined that thin walls shearing apart at the layer lines, is the
more prominent design constraint.
The more valuable outcome from this testing identified an unknown-unknown
within how the tether is secured to the wing. Most knots can be classified as
slip knots, because they bind to the object after the knot is complete. So, the
original design called for a non-slip knot to ensure the line does not tighten
against the anchor pin. This testing showed that non-slip knots only hold about
30-40% of the full strength of the line, and would have likely been an
unanticipated source of failure during the initial flights. The revision is
simple and elegant, where the tether now secures to a spacer which slides around
the pin. But that small change required a complete redesign of the inboard endcap,
which would have been impossible to implement if the platform had already
been constructed.
“Failing fast” is a nice mantra, but whenever possible... make sure it happens
in the lab and not out in the field.
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When Zephyr Plateaus...
Bring the Product to Market Anyway
Imagine a phone that never needs to be charged... but you can only use it
inside your home, and it only works during the summer months. Would you
buy that phone?
While battery life is a major consideration, the primary objective of a
smart phone is to stay connected on the go. So, in this hypothetical example,
having a nice feature (never needs to be recharged) doesn’t have much
significance if it can't deliver the primary functionality (make mobile calls).
Airbus is planning a new spinoff to commercialize their Zephyr solar-powered
aircraft, with a goal of beginning commercial operations by the end of next year.
Back to our original analogy, solar-powered flight is the nice feature...
but the primary function for a High-Altitude Platform Station (HAPS) is to
deliver wireless connectivity year-round across the planet. While I love the
engineering that has gone into the Zephyr aircraft, it is still only
operational under ideal solar conditions. This platform has been optimized
time and time again for the past twenty years and is still limited to a
narrow range of latitudes only operating during a few summer months.
Their stated objective is a 200-300 day endurance, but from a previous
post (https://lnkd.in/epptPnWr)
their batteries only appear to last for 64 days. And with test flights
limited to about 30 deg latitude, their coverage would primarily service
the Sahara Desert and the Pacific Ocean.
While fixed-wing aircraft cannot attain the primary HAPS objective,
Devorto pioneered the Tethered Uni-Rotor Network (TURN) to specifically
address the main technical challenge needed for solar-powered persistent
flight. NASA - National Aeronautics and Space Administration and United
States Air Force R&D funding show this solution will persist at 65 deg
latitude (98% global coverage), while carrying a 68 kg (150 lbf) payload.
The entire Zephyr 8 is only 65 kg... if Airbus wants Zephyr to provide
global coverage, perhaps their best option is for TURN to just carry
it wherever it needs to go.
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