Present Segway Batteries
Unchanged in Software Update
Software Upgrade Alerts Segway Riders Sooner to Low Battery Condition
by Donald GeorgiWhen Segway LLC (www.Segway.com) received 3 reports of Transporter riders falling because of a lack of available battery power, a voluntary recall in cooperation with the U.S. Consumer Product Safety Commission on September 26, 2003 was initiated. Mimicking the venerable ‘Chicken Little,’ various news sources blamed the battery in their headlines to an unaware public. Just six days after the recall, the headline at Fredricksburg.com (see www.freelancestar.com/News) read “Batteries may cause scooter accidents.” Two days earlier the San Jose Mercury News had touted a story with the Title “Two-wheeler tips over when battery depleted.” This second title is not as incriminating as the first headline, but it definitely implied that battery problems cause failure.
The Human Transporter created by Dean Kamen of Segway LLC is a revolutionary device for personal commuting. With the simple shifting of body weight, the rider controls starting, stopping and speed from energy stored in two rechargeable Nickel-metal hydride batteries. (Photo is courtesy of Segway LLC.)
Batteries are the catchalls for a myriad of problems whether real or perceived. Any motorist who has been driving for a few years will remember blaming starting battery problems not on the lack of battery status information, but on the battery itself. Nuisance battery failures may extend to a very untimely dropout of a cell phone during a big contract negotiation or a marriage proposal. Whatever the situation, the battery always catches the blame. Why don’t we blame the gasoline itself when our fuel tank runs dry on the freeway?
Three models of the Transporter are affected by the recall: (from left to right, the ‘i’ series, the ‘p’ series and the ‘e’ series. Approximately 6,000 Transporters have been built with only the three incidents which have triggered the recall. Owners can call the Segway LLC toll free number 877-889-9020 to initiate receipt of the software upgrade which will alert the rider sooner to excessive power demands or low battery condition. The ‘e’ and ‘i’ series are powered by 60 cell Nickel-metal hydride batteries to provide 6, 8 and 12 m.p.h. speed with 5-15 mile range. In the ‘p’ series, each battery consists of 48 cells, to provide a lower peak speed of 10 mph and range of 4-12 miles. The batteries are not involved in the recall. (Photo is courtesy of Segway LLC.) +
In the case of this transporter, less power available at the end of discharge can cause instability , but only because the Transporter is called upon to deliver performance beyond the present maximum power available from the battery. Although the handlebar’s panel indicator shows a red battery low indication with an audible alert and stick shake, there have been three situations where people continue to ride, leading to a fall. While not a condition which can be overlooked, the numbers are not suggestive of a big problem. There are 6,000 Transporters in the field and if we think of an average distance of 10 miles per day, they would cover a total of 22 million miles a year. That would be about 7 million miles per incident, which is not a negitive characteristic. Compare that to the fact that U.S motorists appear to be comfortable with the 40,000 highway deaths each year which equate to about one per 1.3 million miles traveled. The auto ‘stats’ don’t even get into the nonlethal numbers.
The Human interface Control Panel is straightforward with only a key lock on the left which selects one of the three speed ranges (0- 6, 0-8 or 0-12.5 m.p.h.) On the right is the battery condition gauge which displays battery charge quantity on a circular bar around the periphery and a face with a colored background displaying a green background when in the operating range and red when the system is either asking for excessive power demands or implementing a safety shutdown. Operator commands are inputted as forward or backward lean of the body on the platform. Turns are initiated from the handlebars. When a low battery alert or an excessive power request is sensed by the software, there is an additional audible chirping and a tactile shaking of the handlebar to tell the operator to reduce power requests.
One might suggest that the display include a state of charge indicator. Such an indication would be difficult to present since the operating profile of the Transporter has a range of power levels. While traveling at 5 m.p.h. on a flat surface the ‘fuel gauge’ might indicate a 1/4 full, tank, but this number could rapidly change as the Transporter gains speed as a hill is encountered and thus instantaneously change to a capacity of less than 1/16 full at the higher demand. To date the simpler indicators are being used and may be best for a rider who is supposed to be attentive to the driving situation. (Photo is courtesy of Segway LLC.) +
Under constant power conditions, a Nickel-metal hydride battery exhibits reasonably flat discharge conditions,1 but the Transporter, which may be cruising at a medium power discharge rate near the end of charge, is not a constant power load to the battery. If the operator suddenly asks for a surge of power, one could think of the battery performance shifting to a higher load discharge curve where the terminal Voltage drops off more sharply. Even if the current is held constant (which it probably isn’t), the total power delivered is reduced.
Another way of thinking of the situation is to consider that the battery internal resistance builds with use. That internal resistance absorbs some of the stored battery energy flowing to the load. We normally think of a weaker battery as being indicated by dimmer lights or a slower starter motor, but when the Transporter system stability requires a certain amount of power for the control gyros, too little available power can disable platform balance.
Exploded view of the Segway Transporter. At the center bottom can be seen the two Nickel-metal hydride battery modules each consisting of 63 cells. To provide proper operation, the batteries send current to two - 2 horsepower brushless drive motors coupled to the drive wheels through a gearbox. (Graphic is courtesy of Segway LLC.) +
Segway designers identify the point at which the rider should discontinue use, but the three reported events highlighted that the region of low power should be extended. That is the basis for the software change implemented in the recall. The original battery condition ‘gauge’ on the handlebars continues to function as before, and the red warning background color of the ‘gauge’ also continues to alert to the excessive power demand. Similarly, the low power audible alarm and stick (handlebar) shake(vibrating) tactile indicators still function. With the new alerts, the rider is notified earlier in the discharge cycle before the battery energy gets so low that platform stability is lost.
With the updated software, a rider who asks for increased speed while encountering a hill will receive the four warnings, indicating that a less aggressive speed should be desired sooner. In other words, there is nothing new in providing operator safety and the batteries have not been changed; only the warningcondition is noted earlier. The condition does not necessarily signal that rider must stop using the vehicle yet, but that less power should be requested. Earlier in the discharge cycle, there could come a point where temporary excessive power demand could initiate the warning, thus allowing the operator to use the Transporter at a lower speed for a considerable amount of time. There is a point, however, where because of the dwindling stored energy in the batteries, the Transporter initiates a safety shutdown, rendering the two wheeled “magic carpet’ unusable. Then the vehicle must be recharged.
For the rider who does not heed the warning alerts, the outcome could still be loss of stability, but then there is only so much an automatic system can do to protect a user who demands operation beyond the system’s capabilities. The shaking handlebar is especially helpful, because as the still-living pilot2 of a small aircraft without stall warning instruments knows, the buffeting which precedes stall is a life saving indicator to take rotely memorized corrective action. In a noisy area, or where the Segway rider is preoccupied, the additional tactile stick shake allows for ‘second nature response’ to automatically back off, as a part of the ‘feel’ of driving.
What are some of the future alternatives to extend operation in future designs? Already there is consideration of using Lithium-ion batteries for greater total energy and range, but these batteries also have a power dropoff as the cycle nears end of charge, so a warning region still is required. One might argue that the battery should provide a uniform power output over the complete operating profile. This could be implemented with a hybrid combination by adding a supercapacitor or peak current battery to be called upon only when the rider demands acceleration or hill climbing late in the cycle. Although depleted when called on for short power demands, the secondary power source could be refilled from the main batteries.
Whatever the technological future for the Transporter, Segway LLC appears committed to providing as safe and reliable device as possible. In order for this new transportation device to make inroads into people’s thinking, continual focus on safety, convenience, and reliability must be pursued.
1. Handbook of Batteries, Third Edition, paragraph 29.4.8
2. Author’s personal experience
A Personal Segway Experience.
When reporting on a topic, firsthand experience is not recommended when it comes to earthquakes and heart attacks. But, when confronted with the topic as exciting as a device such as the Segway Transporter, firsthand experience is definitely a positive approach. Before getting to the details, let me say that I walked away being totally enchanted with the Transporter, mulling thoughts of how to justify the purchase.
That feeling was not part of my initial thoughts as I walked into the TEAM RAVE Segway dealership in Rochester, Minnesota. Here was set of wheels with handlebar which appeared to have been sired by a hand cart and a misguided artist with old bike parts and a welder in hand. When ‘this thing’ grows up, I thought, it will want to be a railroad locomotive.
But for now ‘this thing’ is a single person Transporter, the brain child of Dean Kaymen who carries significant credentials as the owner of approximately 100 patents and the creator of a portable dialysis machine. Not overlooked is his current challenge of a Sterling engine generator which provides purified drinking water from the engine heat while supplying 300 Watts of electricity.
‘Nuff of the business info; it’s time to take hold of the handlebars. Trepidations reign! Without its ‘kickstand’ (officially known as a parking stand) this relative of R2D2 would be flat on its face, or handlebars. Recalled images of President Bush falling off the Transporter as he got on for the first time add to my fear. I didn’t even want to be president and now I am supposed to do him one better? Will I get a call tonight asking how I would clear up the Iraqui problems, or would I just be boxed up with concrete skid marks on my nose and be buried alongside a couple of brave Civil War Soldiers?
Holding the handlebars is easy! I am in control! But then the salesman tells me to step on the platform. This is another story...but as I do step aboard, the five internal gyroscopes recognize me as a wimp rider who needs all the inertial assistance it can provide, stabilizing the platform while giving me the feeling of solid unwavering support to body and feet. Still my hands have the same sweaty sensation as they did during my first few seconds of learning to ride a bike and in making my solo flight. The next seconds were a new experience; I felt like I was going to stay aboard and continue to live without pain or humiliation. Now what? Others had leaned forward, so maybe I should too...just a little...I am creeping forward. Confidence starts to fill me as I continue to lean and go forward. I am the master; the Segway is my slave! I continue to speed up. It must be all of one mile per hour, and I gain more confidence.
To be a true conqueror, I must demonstrate going backward, but first need to stop this thing without handbrakes. I stop leaning forward and do stop. Amazing! A quick glance from the corner of my eye shows no obstacles behind me, so I gently lean back. ‘Seggy’ (we are now on a nickname basis) follows my lead. I am going backward, not too fast, but quite acceptably, and the feeling of dominance continues to increase.
With a few more forward moves, reversea and turns in the showroom, I am ready to explore the back storage room with its narrow corridors and obstacles. The salesman probably is developing gastrointestinal cramps as he sees me disappear from the showroom, but he does not let on, lest he has his jacket buttons ripped off in disgrace at the next morning’s reveille. I am in control in the maze, and the Transporter follows my every wish. As I am cruising, perhaps a bit too fast for my real skill level, a giant cardboard box looms in the aisle ahead and I stop leaning forward but also cowardly put my right had out to cushion the crash. It does not come. The Transporter has stopped within an inch of the box. I am unharmed, but just a little disappointed with the wimpy lack of confidence displayed in placing my hand forward to cushion the impact which never came.
The literature has stated that the Segway turns in its own radius, and the cramped quarters dictated this as a time to check out that claim. Gently turning the handlebars, I rotate 180 degrees and return to the showroom where the salesman experiences a noticeably lower involuntary pulse and respiration rate. I am smiling. He smiles like a young child who needs a fresh diaper. There is still a large plate glass window for me to uncontrollably challenge, but it is not on today’s agenda.
I stop, get off and try to appear like Eddy Rickenbacker just crawling from his cockpit, but internally, I am both gratified that I still live, and simultaneously, am a master of a two wheeled ingeniously designed mechanism which from appearance should no more capability to perambulate than a wingless bird. Today, I am Icarus, but I have not flown into the heat of the sun and have returned victorious!
The confidence, of riding, the exhilaration of the control and the possibilities for this machine begin the thinking of how to acquire one. What would life be like without it? Dull? Slow? Hot (as opposed to cool)? I would stand out in crowds without wearing the special trousers with the spread of peacock feathers in the rear. I would be known as the man on the go. Only one problem stands in the way, and that is the $4,500 needed to take it from the showroom without attracting police attention. My wallet cries. I have only enough dollars to rescue my car from the parking ramp and pick up a fast food salad with coffee tonight. Humiliatingly, I slink off into the street trying to blend in as a commoner. But, my soul lives renewed in confidence because it knows I have experienced and mastered a new way to travel.