In brief, every component of the Segway PT that is critical to the device retaining it’s self-balancing function is “doubled up” so that if one part fails the other can take over completely. For example, there are two batteries, two identical but independent computer control boards, a pair of double-wound electric motors, and more than twice as many “gyroscopes” than the minimum required to know which way is up (there is triple-redundancy in the pitch axis).
“Redundancy” is a key feature of equipment used in mission-critical applications. It is common in medical equipment (Dean Kamen, the inventor of the Segway PT is famous for his inventions in the medical field). It is also found in military machines, public utilities such as electric power generation, and in corporate computer networks.
Returning our discussion to vehicles, and to electrical vehicles in particular, perhaps the most famous electric vehicle of all (well, after the Segway PT) is the Lunar Rover.
Four of these were built by Boeing in 1970-72, of which three made it to the moon on Apollos’ 15, 16 and 17 respectively (Apollo 18 was cancelled). When you’re 400,000 km from home you can’t just call a tow-truck, so the engineers built in redundant subsystems not dissimilar to those used in the Segway PT. Here is a description by writer Paul Charman, as featured in NZ Herald’s Driven section (19 June 2013):
Each wheel was individually powered by a 190 watt motor, for a total power of 750 watts, or one horsepower (the same power output as a Segway PT). The vehicle’s top speed was 13 kph on a relatively smooth surface, and the range 65km.
Two 36 volt batteries provided the power, although either battery could power all vehicle systems if required. The front and rear wheels had separate steering systems but, if one steering system failed, it could have been disconnected and vehicle would have operated with the other.
Centralised controls allowed either astronaut to drive the vehicle.
Segway i2 and x2 models feature advanced Lithium ion battery packs as an integral component of their extraordinary performance – long range-per-charge, many years of excellent day-to-day use, and usability across a wide temperature variation.
Segway, Inc. is a world leader in the field of battery energy management in the context of electric vehicles. Regenerative braking is key to the range-per-charge that can be achieved by a Segway Personal Transporter (PT) – up to 38km from an i2 and more than 20km from an x2 (under ideal conditions). When a rider de-accelerates or coasts down a hill, the electric motors act as generators and recharge the batteries. Not all energy is recovered, of course – some is dissipated as heat through losses (air resistance, friction in the gearboxes, heat generated in the electronics and motors, etc). As an example, Segway engineers have commented that about one third of the energy taken to climb a hill is recovered going down the other side. Maximum regeneration occurs at “medium” speeds, because at lower speeds the fixed losses cancel out regeneration, and at higher speeds air resistance becomes increasingly significant (because doubling the speed increases resistance by a factor of four times). Segway’s experience in this field contributed to Team Segway Racing MotoCyzsz’s historic victory at the Isle of Man TT Zero this week.
The Segway PT combines hardware and software in an unique way. The three key elements – motors, microprocessor controllers and batteries – are in constant communication with each other under software control, managing the flow of energy between the propulsion sub-system (motors, etc) and batteries. What makes the system particularly complex is that the Segway PT has full “redundancy” – or at least two of every essential component. Each of these components is independent from the other. For example, each motor is double-wound (i.e. two separate sets of intertwined windings, or effectively two motors in one), there are twin identical controller boards running the same program simultaneously and checking up on each other hundreds of times per second, and there are two separate battery packs each containing their own intelligence that monitors a variety of internal parameters (including temperature). There are also more gyroscopes on board than are necessary.
What this complete set of redundant systems means is that the Segway PT can remain upright and safely in balance even if one component – or even one of every component – were to fail at exactly the same time (i.e. one set of windings, a controller board, gyroscope and a battery). Over the years Segway, Inc. has developed more experience in this field than any other vehicle company. For example, while Toyota deals with regeneration of Nickel batteries (not Lithium) in this Prius range of cars, there are no redundant systems adding complexity.
Segway, Inc. has contributed their expertise to the General Motors EN-V, to Segway Racing’s 1st and 2nd place winning debut at the Isle of Man TT Zero electric motorcycle race in 2011, and their 1st and 3rd place in 2012 (where both of their EV bikes became the first in history to break the 100 mph lap speed). Aside: Scotsman Bob McIntyre broke this record in 1957 on a conventional bike, and New Zealander John Britten achieved the world record for Fastest Top Speed at the TT with his hand-built Britten V1000 in 1993.
Valence Technology builds Segway Lithium battery packs using their patented ‘Saphion’ brand Lithium Phosphate chemistry. Saphion is a very safe, stable Lithium chemistry and construction.
Saphion was specifically developed to be safe when used in transportation devices and in other extreme conditions. These batteries are widely deployed across the Smiths Electric Vehicles commercial range, on boats and in other difficult environmental applications, and of course in Segway PTs.
One of the unique benefits of Saphion is protection from thermal runaway: should a battery catch fire it will be limited to one cell and then die away. In traditional Lithium battery packs fire quickly self-propagates from cell to cell resulting in a thermal event that rapidly increases in temperature and ferocity (“thermal runaway”). This makes it very difficult to quell. Here is a video showing what happens to a common rechargeable Lithium battery compared with a safe Saphion when both are set alight.
All types of Lithium batteries are considered Dangerous Goods on aircraft because a battery fire could quickly overwhelm the fire extinguishers built into the hold. Regulations do not discern between the various Lithium chemistries, despite the inherent safely of Saphion. This prevents Segway batteries from being taken on passenger aircraft. With the correct documentation and packaging they can be carried on cargo freighter planes.
Segway, Inc. accounts for about 20% of Valence’s annual sales. For more information on Valance and its products, here is an interesting summary about the company by a share market analyst.
The very earliest Segway PTs were fitted with Nickel Cadmium (NiCad) battery packs, although none of these i100 models were sold to the public (they were used within the company for testing purposes, and may be been trialled by a small number of corporations/institutions during 2002). When launched to selected corporate buyers in 2002 and then to the public in 2003 the i167 model was fitted with Nickel Metal hydride (NiMH) battery packs. Later in 2003 the smaller p133 model was also launched with NiMH battteries, as was 2004’s i170 model. When the i180 was launched in 2005 buyers could choose between NiMH and Lithium at time of purchase, and a software upgrade would enable the i167 and i170 models to use Lithium packs also. Later that same year, the Segway GT (golf transporter) and XT (cross-terrain transporter) models became available and shipped only with Lithium batteries so that these models would have useful range under their intended operating conditions. With the launch of the i2, x2 and x2 Golf models at the end of 2006 Lithium batteries became the only option.
Segway New Zealand’s experience with Segway battery packs has been that they are both reliable and durable. While few of the oldest NiMH batteries manufactured in 2002 and 2003 are still functional or offer any useful range, dozens of owners in 2012 are still using Segway PTs fitted with NiMH batteries manufactured between 2004 and 2006. These tend to be battery acks that have had light-to-moderate use over the years. All NiMH battery packs that had high personal use or were deployed in commercial roles were exhausted several years ago.
Segway Lithium batteries were a leading-edge technology in 2005, and since then we’ve noticed improvements in capacity (range-per-charge), reliability and lifespan as Valance’s manufacturing processes and the battery management software have improved. We estimate that about half of 2005-6 batteries (AB and AC battery software revision) had reached the end of their life by mid-2012. Most batteries from 2007 (AF software revision and later) are still performing surprisingly well – even those fitted to Segway PTs in commercial applications with well over 10,000km on the odometer.
Here are some New Zealand examples of the exceptional performance achieved with Segway Lithium battery packs. At Canterbury University two first-generation HT i180’s fitted with Lower Cargo Systems have been delivering mail since mid-2006, and their Lithium batteries (AB) only required replacing in 2011. Quite a number of Segway x2’s deployed in demanding security patrol roles around New Zealand have delivered useful work for more than 15,000km per pair of batteries. These are machines that travel 20 to 30 km every day, 365 days per year. On this basis, we expect many i2’s to deliver more than 20,000km useful life from a pair of batteries, though none we are aware of have yet reached this milestone on their odometers. One private owner in New Zealand estimates his i180 has travelled well in excess of 25,000 kilometres (this model does not have an odometer).
THE FACTS ABOUT A SEGWAY PATROLLER’S BATTERY RANGE
Segway® is the world’s leading provider of electric personal transportation. Our Segway Patroller is the world’s indisputable #1 personal transportation solution for police and security markets.
We are often asked, “What is the battery range of a Segway Patroller?” Consistently, the answer is completely satisfactory to customers, which is why we hold the market position we do. The Facts:
The Segway Patroller can travel up to 38 kilometres on a single charge, more than enough for public safety personnel patrolling a neighborhood, business district, university campus, shopping mall or corporate center.
The Segway Patroller has an on-board charger and patented battery technology that allows officers to charge it at anytime and anywhere there is a standard electrical outlet.
Officers can top-off the batteries or partially charge them to extend range whenever they are not riding, without any reduction in battery performance. Today’s electric three-wheel devices or golf carts must return to a fixed charging station, connect to a bulky off-board charger and fully charge the batteries or risk damaging them.
Segway Patrollers can remain in the field and extend their range with a common electrical power cord. For example, the Washington, DC Metropolitan Police Department recently reported that its fleet of 80 Segway Patrollers is used around the clock throughout the city. They point out that their Patrollers infrequently, if ever, fully deplete their battery charge.
In the rare event that an officer did need to significantly extend the Segway Patroller’s range, he/she could do so by swapping out batteries. This process can be completed in less than 5 minutes using a basic hex wrench. Using Segway cargo accessories, officers also have the option to carry light, compact and fully charged Segway batteries. If necessary, batteries can be swapped out in the field during a shift. This option is not available with the large batteries of today’s electric three-wheel devices or golf carts.
Segway is one of the world’s primary users of large format batteries. The Company was at the forefront of Lithium-ion battery development for personal transportation. We’re experts in smart battery management and the advanced sensing technology required to extend battery life and maximize energy efficiency. Please click here to download detailed information on Lithium-ion batteries.
In most circumstances, it is best practice to replace Segway battery packs in pairs because a Segway PT only performs as well as the weaker pack attached to it.
Segway Lithium batteries contain 92 cells, and NiMH batteries contain 60 cells (48 for p-Series) – see photo in Panel 3 higher up this page. Batteries are considered a ‘consumable’ and by their very nature will exhibit a fairly wide range of lifespans. Some last shorter than average, some longer. Sometimes, batteries will fail spontaneously before they are “worn out” (this is analogous to going out to start your car on a winter morning only to find the battery suddenly dead today, yet it was fine yesterday). Remember that all batteries slowly degrade chemically from the day they are manufactured, whether they are being used or not. Every battery needs to be replaced eventually.
Our feeling is that if you’re not wearing out your batteries, you’re not using your Segway PT enough – so get out there and enjoy your incredible machine!
[This article was first published in 2012 and was updated with additional information in 2014]
Journalists love to use the phrase “a bit like a Segway” in stories, as they scramble for ways to describe a wide variety of new devices or proposed designs. Yet, usually, the object is not really “like” a Segway Personal Transporter (PT) at all.
For example, take this “Segway for the air” story that appeared online this week, about the E-volo, world’s first electric mutlicopter. This device balances and hovers in the air automatically and – like the Martin Jetpack – is controlled by a simple “fly by wire” joystick while computers, gyroscopes and other sensors do the heavy lifting control. The first link includes a video of the first flight, and this one includes some alternative design illustrations.
The E-volo is a fascinating design, and perhaps the natural extension of the Parot AR Drone. But with the pilot sitting atop 16 spinning blades, it could all end rather badly…. That said, like the Segway PT it has redundancy built in, and can continue to operate safely even if up to 4 motors and blades should fail. In Engineering, the term “redundancy” means duplication of capability to increase reliability, so that in the event of a failure of one resource the “spare” resource ensures continued normal operation.
Readers of Segway New Zealand News archives can find our coverage of other self-balancing devices, including the SoloWheel, the YikeBike, a one-wheeled motorcycle, and the telepresence Anybot.
At 60cm diameter, the Groundbot is larger than it appears in the video in the link above. It weights 25kg, cruises across seal, sand, snow, mud and….because of its low density….it even floats!
Many universities and research labs are experimenting with self-balancing machines. For example, the Coordinated Robotics Lab at the University of California San Diego has built the iFling, aradio-controlled robot described as a “self-righting little Segway-like vehicle” designed to pickup and throw ping-pong balls. The video shows just how incredibly agile this device is, and how cleverly the design has been refined over three iterations.
Here in New Zealand, Auckland University purchased two Segway PTs in 2005. One of these is regularly dismantled and reassembled by Mechanical Engineering students as part of their degree. The platform has been made self-balancing and capable of remote control, and these enterprising young minds have also been known to fit it with a “frickin laser beam.”
Researchers and businesses looking to build their own applications that utilise a self-balancing platform can use a Segway RMP Robot Mobility Platform. The Segway RMP range offers a family of statically and dynamically balanced platforms that offer powerful, robust solutions with exceptional range and capabilities.
Segway New Zealand News 