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Originally Posted by Dave Flowerday
OK, first of all, I'd say there's enough disagreement (not just here, but in general on the web) that we're not going to change each other's minds. Because of that lack of concensus, though, it hardly seems fair to chastise others for using the phrase contradictory to the FAA, especially since most of the writing on the subject with regards to robotics seems to be differerent than the FAA.
With your wheel encoder, are you really measuring your movement over ground directly? I don't personally think so - you're measuring rotations of a wheel, which only has an association with ground speed because you expect that wheel to be in contact with the ground, to rotate a certain number of times per distance traveled and to not slip. This seems to me to be no different than navigating in an airplane using airspeed - using your airspeed combined with knowledge of winds etc. you think you know your groundspeed, but you can't be sure.
If you put your robot up on a platform and spin your encoder wheel, your robot will think it has moved, won't it? Again, your robot assumed it was measuring groundspeed when it actually wasn't.
Anyway, it's clear we disagree on the definition, so I don't expect you to change your mind and you shouldn't expect me to change mine. I understand your reasoning and accept it, but I still personally believe the prevailing definition of dead reckoning in the world of robotics to be the one I described.
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Okay, we'll agree to disagree. I figure you would want systems like yours to be distinuished, rather than being lumped in with everyone else's. Anyway, can we agree on "open-loop" and "closed-loop"?
This is a good lesson as far as showing how two cultures can clash. As the kids on South Park would say, "we've learned something today..."
Everyone should take this to heart, as this type of thing happens every day around the world. I thought Dave was an idiot for not knowing the definition of dead reckoning (based on the definition that I know), and he thought I was an idiot based on the definition that he knows. Are either of us idiots? No (okay, okay, I don't want to hear any snide remarks). However, our different backgrounds lead us to think that way.
This is very typical in a global corporate setting. Each culture has different expectations about the ways things are supposed to be, and if you don't understand that, you can think some pretty bad things about people without knowing the truth. For instance, our European office thought that our American engineers don't care what they're saying because we don't keep eye contact 100% of the time, while most Americans would interpret 100% eye contact to mean that they are angry or being intrusive. Anyway, that is one small example, but the point is this: if someone does something that to you seems inappropriate or stupid - you may just need to do some investigating to determine the true intentions. You'd be surprised at what you'll find out.
Lastly, I'm sorry for getting wound up. I had one of the most frustrating days of my life here at work today, and my blood pressure was probably through the roof today. But that doesn't mean I should go over the top here on you guys. I apologize.
Just a couple of side note for fun:
- the wheel is MUCH more accurate than aircraft groundspeed calculations.
An airspeed indicator can vary by a few knots in ideal conditions, then it changes in accuracy depending on the temperature and altitude (at 5000 ft on a hot day, your airspeed indicator can read as much as 15 knots low). Throw in the fact that winds aloft forcasts are rarely more accurate than +/- 5 knots and the direction is rarely better than +/- 30 degrees, and your compass is allowed to be off by 5 degrees, and you can start to see how aircraft dead reckoning can hardly be compared to a measurement wheel and a nice angular rate sensor. I guess when you are used to the horrible inaccuracy associated with aircraft dead reckoning you don't want your robot to be associated with that inaccuracy - too many bad connotations.