Krumlink

Why not use Infrared? Wind cannot blow it off course, and it is perhaps better in this situation as a distance measurer, as ultrasonic cannot be very effect as proven in FRC, we used IR in a type of control circuitry, and we NEVER had a problem with it. Ultrasonic in other robots (team 148) have had problems. IR is better for distances, and Ultrasonic is better for object sensing.

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MechTronics

dknguyen

Ir might be affected by sunlight, which may or may not be worse than the wind. My theory is that sunlight gives you a false reading, while ultrasonics would give you no reading (hopefully). I'm not sure what is worse:

-responding incorrectly to a false IR reading
-or not reacting at all to a noised-out ultrasonic echo because you it doesnt think the ground is there at all

My theory is that the ultrasonic echo would be able to be picked up once it got closer to the ground, when it matters most in bad conditions but still let it see the ground farther away in good conditions.

But the main reason was because of the lower minimum and higher maximum range.

BUt I don't know how each would fare right now. I admit that I am also more biased to ultrasonics as I trust TOF more than parallax measurements and like bats. (THey seem to use ultrasonics for UAV automated landings. I'm fairly certain it's because you have a range envelope for a single sensor.)

I do have some Sharp IR sensors lying around though, and it's far easier to imeplement them than ultrasonics because everything is already done for you.

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Krumlink

why not test each method?

Test in:
Sunlight
Wind
Noise
Other things?

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MechTronics

dknguyen

Your insistence on IR has given me the idea to use the largest IR rangefinders I can find:
http://www.acroname.com/robotics/par...Y0A700K0F.html

To use them as side-sensors rather than ground sensors. THe ground sensors need a low minimum range so it doesn't lose sight of the ground just as it's about to land, and long range so it has a good lead-time to know that the ground is coming.

But for side sensors, so it doesn't side drift and smack into me or anything else while it's taking off or landing, the minimum range of 1m of the IR sensors is okay (since the rotor blades are 1m in diameter anyways, and if anything gets withing 0.5m of the rotating blades...it's all over anyways. I think outward facing sensors would be more affected by the rotor downwash than downard facing sensors, so IR is probably better than ultrasonic for that case.

THey need to be calibrated though which is a bit of pain. Another reason I like TOF measurements.

Still not sure how to actually make sure it's stationary over the same patch of ground as it's landing though. That side thrust from the tail rotor is a pain.

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killivolt

My thing of imagery was not to take a picture. It simply has to focus on an object. If you had a distance at 20' to an object as you approach it the focus ring turns. If you had a 0-20' measurement you could attach a gear on the outer edge and then add output gear attached to a shaft of electrical adjust resistance or something measure it giving it a distance ? or magnetic showing how many clicks equal to X distance ?

Orientation I'm not sure. Tail yaw I think of Magnetic north as 0 and 360 degree orientation on the outer edge.

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