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Segway Recalling 23,000 Scooters
DocJohn writes, "For the second time in 3 years, Segway has announced a recall of all Segway Personal Transporters. The problem described is that the Segway 'can unexpectedly apply reverse torque to the wheels, which can cause a rider to fall. This can occur when the device is tilted back by the Speed Limiter and the rider comes off and then back onto the device within a short period of time.' A software update is needed to fix the problem." This AP story mentions President Bush's 2003 stumble on a Segway without speculating on whether the cause was the software glitch behind the current recall.
This doesn't surprise me. It's just another example of how easily programmers fall into the trap of common "use cases" when writing software. Too often, programs are written on the assumption on a simple linear chain of events driven by a use case. In the Segway example, it would appear that the people who wrote the control logic for the scooter assumed that people would get on the machine from a full stop and get off the machine at a full stop. Remounting the machine during the stopping process violated this assumption and exposed a fault in the control logic. I see this type of problem all the time on e-commerce sites (even Amazon.com has the problem) when the buyer attempts to unroll part of a transaction to change something or check an alternative path in the buy/ship/bill/confirm cycle.
The point: always assume the user might do anything at any point in time.
Two wrongs don't make a right, but three lefts do.
Segways are like fat chicks. They're both fun to ride until one of your friends sees you.
Where does the school board find them and why do they keep sending them to ME?
That's not due to a software glitch. That's a special feature...
Bush fell off of the unit because it wasn't turned on in the first place. He never keyed the unit to power, nor switched it to what's called "Balance Mode" - most of the introductory material highlights this extremely well. He took it out of the box and then stood on it. You're also supposed to charge it before use to condition the batteries, which he also failed to do.
Also, "reverse torque" wouldn't cause him to fall -forward- unless he managed to have corrected it and somehow caused a wheel to spin out on flat, regular asphalt, which is nigh impossible.
I'm honestly not too concerned with this recall - it seems like it happened when people first started to learn how to use the units, where they would get freaked out by the unit tilting back to warn them of the unit's speed limitations, and then stepped off. Jump right back on, and bad things -can- happen, apparently.
-Jordan