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| From: | gisela.noci |
| Subject: | RE: [Paparazzi-devel] RE: distance measurement for landing. |
| Date: | Fri, 13 Nov 2009 07:45:19 +0200 |
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VERY NICE!!!!! I have not seen this one
yet. This one will work very well as a good flying altitude control sensor. My
only complaint is that the ranges available go from 10PSI to 20PSI – 15PSI
is really what we need to cover sea level upwards (1034mbar approx 15PSI). So
one could use the 20PSI sensor, but then we are back in the same box – we
through away ¼ of the sensor’s rsolution, but that still leave
18bits to cover sea level upwards. Good find Sergey! BUT, you still should not try to land
based solely on this sensor….You will still fall prey to the atmospheric pressure
variation of the moment at the landing location, and you only need to be a
meter out…. However, the use of differential sensing
with a sensor of the reported accuracy has great potential, ie, a sensor on the
ground and using the change from lauch to land to correct the A/C pressure alt
when landing. With a robust landing gear, this has possibilities…. Joe From:
address@hidden
[mailto:address@hidden On Behalf Of Sergey Lukin Hi Joe, On Thu, Nov 12, 2009 at 6:39 PM, gisela.noci <address@hidden>
wrote: The radalt link is in fact NOT UWB; it is a
conventional radalt, at microwave frequency, and works by varying the frequency
of the transmitted pulse, and then looking at the difference in frequency of
the transmitted pulse and the received pulse. The phase shift is in essence
measured and the range calculated. This is the classic Doppler effect. Also,
the implementation is by its very nature large, heavy and power hungry, maybe
10watts at least. UWB is the transmission of a single, very
fast ( less than 1 nanosecond) pulse, and then detecting is reflected return an
measuring the time it took to go and come back; exactly the same as ultrasound
ranging, except the transmission is at ‘light speed’ . If you have
good oscilloscope and are an electronics hobbiest, you can put together a simple
demonstrator; however, to do autoland with one requires it to be far more
accurate, etc. Regarding the webcam solution, fine for
very short range (1 or 2 meters), will not work in bright light ( CCD
will saturate) and suffers the same problem as the ultrasound; poor
reflectivity of the signal from the ground surface. ‘Real’ laser
rangfinders use a high energy pulse of laser light, in the order of 10s of
watts, sometimes even 100s of watts, for very short periods, also in the
nanosecond or sub-nanosecond range. The rest is the same as for UWB, it is
simply a time of flight measurement of the pulse to reach and reflect of a
target, back to the source. High energy is needed because of poor ground
reflectivity….As I said some mails ago, no magic bullet here..Yet….. Joe From:
paparazzi-devel-bounces+gisela.noci=ate-international.com@nongnu.org [mailto:paparazzi-devel-bounces+gisela.noci=ate-international.com@nongnu.org] On Behalf Of Sergey Lukin
Subject: Re:
[Paparazzi-devel] RE: distance measurement for landing. Hi guys,
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