CASE STUDY
Creating “Empowered Pedestrians” with ANSYS Multiphysics
S E G WAY L L C
Introduction
“It” was a design engineering project shrouded in a veil of mystery. A cryptic posting made to the Web site Inside.com sparked a wild amount of anticipation and speculation about “It.” Rumors spread throughout the engineering community that the project designated by the moniker “Ginger,” would be one of the most significant advances in transThe National Highway Traffic Safety Administration has already ruled that it does not consider the Segway HT a vehicle, thus freeing it from the operating restrictions — and necessary operator’s licenses — of cars and motorcycles. It is Kamen’s goal to see the device become a common site on urban sidewalks throughout the world. respond by moving the device in the appropriate direction.
EXECUTIVE SUMMARY
portation technology ever devised. Different reports identified the device as everything from a hydrogenpowered hovercraft to a magnetic antigravity device to a matter transporter right out of “Star Trek.” As it happened,
Challenge:
Calculate performance of multifunctional components, with nonlinear designs, on unique self-propelled scooter
Challenge
The Segway HT packs a multitude of hardware and software components into a disconcertingly small space. “It’s a bit like packing eight pounds worth of stuff into a five-pound bag,” quips Mike Martin, head of the Mechanical Integrity group at what is now known as Segway LLC. One of the responsibilities of Martin’s group is to ensure that the features and functionality designed into the Segway HT conform to specified performance criteria. The group works closely with Segway’s Design & Release team of design engineers, performing structural, thermal and noise/vibration/harshness (NVH) analyses on everything from components and sub-assemblies to full assemblies. Very often, the Pro/ENGINEER files that emerged out of the Design & Release group were composed of odd geometric configurations that rendered standard mechanical analysis techniques ineffective or extremely difficult to conduct. In particular, the Segway HT’s chassis presented the Mechanical Integrity group with a number of simulation challenges. The chassis was to be constructed to accommodate the weight of an operator up to 250 pounds, while simultaneously acting as housing for the device’s motors, batteries and electronic components. Naturally, the chassis had to be strong enough to meet these standards while being lightweight at the same time.
“Ginger” emerged as the Segway Human Transporter (HT), a two-wheeled, self-propelled scooter somewhat reminiscent in
Solution:
Analyze designed components and assemblies in ANSYS Multiphysics
appearance to an oldstyle push mower. by Invented
M a n c h e s t e r, N . H . (U.S.A.) entrepreneur
Image courtesy Segway LLC
Dean
Kamen,
the
Benefits:
Easily able to accommodate Segway HT’s large and complex design issues Successfully predicted areas of stress and fatigue on numerous components Instrumental in design of proprietary physical fatigue-testing machine
Segway HT is posited to have the same impact on personal transportation as when the automobile replaced the horse and buggy. At the heart of the Segway HT is a complex bundle of gyros and sensors that imitate the human body’s ability to maintain balance – a process billed as “dynamic stabilization.” While the Segway HT possesses no engine, throttle, gearshift or steering wheel, it can transport the average rider for a full day, non-stop, on little more than a nickel’s worth of electricity. The Segway HT’s sensors detect the subtle weight shifts made by an operator’s body when walking and
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“ANSYS Multiphysics is limited only by the performance of the hardware on which it is installed,” Mike Martin, Segway LLC.
CASE STUDY
Early on, the Segway HT was purported to be everything from a hydrogenpowered hovercraft to a matter transporter right out of “Star Trek.”
A specific area of concern arose at the interface between the control shaft and the chassis (below). Not only was this base designed to attach the device’s handlebar control shaft to the chassis, it would also be engineered to house the machine’s electrical re-charge unit. These specifications lead the Design & Release group to render a design which “is full o f ‘ s w o o p y ’ c u r v e s , ” as Martin himself puts it. Consequently, there was no way to predict its performance using simple pencil-and-paper calculations. Mark Wyer, also an analyst with the Segway Mechanical Integrity group, points out the usefulness of ANSYS Multiphysics in the stress and fatigue analyses of the Segway HT’s numerous components and assemblies. “Because the Segway has a number of sudden geometry changes,” he says, “the potential for high stress levels exists.” Wyer used ANSYS Multiphysics to predict the location of stress/fatigue “hot spots” on numerous areas of the Segway HT. For instance, on the wheel model (shown below), ANSYS Multiphysics accurately predicted the load conditions the Segway’s wheels would see in regular usage. These predictions were verified via physical tests on a specially designed fatigue-testing machine the team developed. Presently, the scooter is being tested as an alternative mode of transportation for rangers at the National Parks Service and ambassadors in the city of Atlanta, Ga. (U.S.A.). Big-name companies such as General Electric and Michelin are also using it as
Images courtesy Mark Wyer, Segway LLC
the mesh so much. With ANSYS Multiphysics, you just throw the model in and, with maybe only a couple of bumps and tweaks, you get a good mesh.”
beginning of its design cycle. However, he does predict its influence manifesting in the numerous Segway accessories yet to be developed, such as a series of device-mounted bags. “ANSYS Multiphysics is limited only by the performance qualities of the hardware on which it is installed,” he enthuses. Indeed, as Mark Wyer points out, ANSYS Multiphysics also played a prominent role in the design of the proprietary fatigue-testing machine utilized by the Mechanical Integrity group. “This helped us to ensure that the machine wouldn’t wear out before the components we tested did,” he observes.
Solution
Before Dean Kamen split the Segway operation off into an independent corporation, it was part of his DEKA Research and Development Company. Under the auspices of DEKA, many other innovative products were brought to light, including the heart stent used by U.S. Vice President Dick Cheney (covered in ANSYS Case Study Engineered to Save Lives: DEKA Redesigns Medical Stent Using ANSYS Software) and iBOT, a 4-wheel drive, motorized wheelchair with — among other features — the ability to actually climb stairs. ANSYS Multiphysics software was instrumental in realizing these ideas at DEKA. Consequently, it was once again utilized to assist the Mechanical Integrity group in analyzing the geometric nonlinearities present in the various design elements of the Segway HT’s chassis. “Since there are no straight lines in the design of the control shaft base,” observes Mike Martin, “there was no other way to get a good handle on its design performance.” He also notes the software’s ability to quickly mesh and analyze large-scale geometries as being key to resolving the most intricate design issues. “In many other packages you have to work
While it may be true that the Segway HT won’t turn lead into gold or transport you to another world, (“Sue me,” jokes Dean Kamen) it nonetheless has the potential to change the face of the urban landscape.
a means of getting around. Perhaps the most significant push for the use of the Segway thus far came in June, 2002. United States Postmaster General John Potter then announced that the Postal Service had purchased 40 of the devices. Although the Postal Service had already tested Segway HTs on routes in the Tampa, Fla. and Concord, N.H. (U.S.A.) areas, Potter said that the Service would expand its test into six other locations throughout the country.
Benefits
Mike Martin anticipates no major changes to the Segway HT’s current configuration, a fact he attributes to the use of ANSYS Multiphysics from the Consumers will also be able to purchase a version of the device beginning sometime in 2003.
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