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Originally Posted by Paul Marshall
Ok, so I have a question. (obviously since i'm posting this) What is the angular resolution of the IR sensors? Now, at first glance you might think this is a stupid question, so let me clarify. By resolution I mean what is the accuracy that you can get, within 1 degree, 0.1 degree. Now, I haven't studied this a whole lot so I may be wrong, but I think that the IR sensor is mounted on a servo and controled that way. So this maybe a quesiton of how accurate is the servo. Or maybe how accurate is the servo and the sensor combined. I'm not sure because I haven't looked at it closely. The quesiton still stands. What is the resolution/accuracy of the sensor?
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The sensors will have a pretty large "window" they can see. The IR detectors they gave us are designed to be used in TV's, VCR's, Stereos, most remote IR applications. Because of this they will sense over a wide range, similar to your eyes. Imagine if you had to be within .1 degree of the front of your tv to change the channel! If someone points a flashlight in your direction you can usually see it if it's somewhere in front of you. The IR sensor (eye) can detect the IR beacon (flashlight) as long as it's generally in front, making the IR sensor alone a very poor way to detect direction.
Joel Glidden posted the diagram from the specs sheet with specifics on angle / detection range above (thanks).
To get around this you need to build some sort of blind for the sensor. Roll up a piece of paper and look through it. This is more or less what you're trying to accomplish with the sensor, you can now only see a few degrees as opposed to 120 (or whatever arc human vision covers). Now you can rotate your head and scan for the flashlight. When you find the flashlight through your rolled up paper tube you know pretty accurately where it is in relation to you (assuming your neck has an accurate enough angle sensor).
Kevin Watson has referred to the following url quite a bit (thanks!) and in it he shows a great way to use the IR sensors:
http://kevin.org/frc/tracker/
Also refer to:
http://www.chiefdelphi.com/forums/sh...ad.php?t=23933
Maybe he will chime in and share some of his wisdom
He setup the sensors in such a way that he will be able to tell if the servo is pointing directly at the IR beacon and if not which side it's off to. Whats really amazing is how simply he does it, probably took an hour at most to build. Take a look at it, it's really neat.
I don't think the IR sensors themselves have any "angular resolution". Instead the angle will be detected by moving the IR sensors around until they are pointed at the beacon.
I'm not sure about the repeatability or actual accuracy of the servos in the Kit of Parts, but theoretically you can set the servo to any of 254 values. I believe the servos can rotate over 270 degrees (sending 0 will move the servo head to 0 deg, 254 will move it to 270 deg), so you should be able to sense in increments of (270/254) or about 1.06 degrees. This should be more then accurate enough to navigate the field in autonomous mode- as shown at kickoff (especially if you use IR sensors in conjunction with dead reckoning or shaft encoders on your drive system). Of course this is all limited by the construction of your sensor assembly. Discussion about servo accuracy/specs here:
http://www.chiefdelphi.com/forums/sh...ad.php?t=23962
Someone please correct me if I'm wrong, I'm not entirely sure about everything I just said
Greg