RE: [Paparazzi-devel] distance measurement for landing.

[gisela.noci]

Morning Andrew.

Not sure what you would like to know, Andrew, but briefly, UWB radar is
based on very similar principals to the pulsed ultrasonic ranging modules.
What I have developed is not a Doppler type ranging system, but a
Time-of-Flight measurement system, and obviously somewhat more complex in
that we are dealing with very short flight time of RF pulses at nominally
300mm/nanosecond compared to the simple hardware detecting sound pulse
speeds in air (around 343meters / second @25deg C)

My prototype hardware is consists of:

A processor ( ATMEL 32UC series @ 40MHz) with an LCD for parameter display,
some pushbuttons to select functions ( Autorange, search at fixed range,
adjust pulse repetition rate, etc)and interface to the  the digital pulse
generator and delay pulse generator, and return pulse detector.

The pulse generator and delay pulse generator consist of Dallas / Maxim
delay lines, which are so arranged to give me a number of ranges, in time ,
from with range steps in 0.25ns, 0.5ns, 1ns and 5ns increments.

The process is to generate a TX pulse, which drives a fast dual transistor
avalanche pulse generator, directly connected to a directional UWB antenna.
The TX pulse also triggers the delay pulse generator, which generates a
pulse according to the programmed delay interval. This 'RX' pulse then opens
the 'receive gate' and looks for a reflected pulse of RF, and integrates it.
This process is repeated a (programmable) number of time, in order to
accumulate the tiny amount of received energy and storing this increasing
voltage in an integrator. When a voltage threshold is reached ( as read bu
the processor via an A/D)the a target is declared as detected. When scanning
for targets, ie, from 200 mm out into space, the delay pulse is slowly
incremented and the above process repeated.

The pulse repetition frequency (PRF) of the pulse is 1MHz, ie, the time
between subsequent TX pulses, and I accumulate 1000 pulse of received energy
before moving onto the next range delay. This is therefore 1ms spent at each
range slot. If 300mm  range steps are used, at 1ms per range slot it would
take 4 seconds to go from 300mm out to 1200meters.

The principal I use is to range at 0.25ns delay increments out to 20meters (
260 steps of approx 75mm range), then switch to 0.5ns delay increments out
to 200meters ( 1200 steps of approx 250mm range ) and then switch to 5ns
steps ( 1.5meters range step size, 666 steps) from 200meters out to 1200
meters and this give a total scan time of around 2 sec, from 200mm out to
1200meters.

Naturally, if using the radar for landing etc, you will only range the
distance of interest, ie, maybe from 200mm out to 20metres, at say 0.5ns
resolution ( 150mm) and this would only take 130ms.

Now, for a reality check.

To achieve 75mm range steps, ie, 0.25ns resolution, requires VERY fast TX
and RX range trigger pulses, of the order of 4 times faster than the ranging
period, ie, around 80 or so picoseconds. Not Possible! Also the antenna
'rings' for longer than that. In essence, the practical pulse widths
achievable without using million dollar components, esoteric PCB materials,
and ultra fancy test equipment, is around 1ns. Coupled with perhaps 1 to
1.5ns antenna ringing, this means around 2 to 3 ns pulse periods, which will
practically give a range ambiguity of 600 to 900 mm, and a resolution no
better than 600mm. 

My intention is to use this radar in flight for a seek and avoid system, one
Omni directional TX antenna an 4 directional receive antenna ( forward,
rear, left and right), and then for landing to use 2 antenna facing ground,
and detecting ground from 50meters down to 6meters, and then switch to
ultrasound for the landing flare.

Right now the hardware is working ok, but I am not happy with the receive
antenna sampler circuit, and am working to improve that. Also, I will later
change to a delay locked loop delay pulse generator for the pulse
generators, since the Dallas delay line route is tedious to program and set
up, and causes 'jumps' in the integrator static level when swapping between
the different step sizes.

So, that's the story - forgive the long mail.

I believe UWB radar is the ONLY way to go, especially for seek and avoid,
and for ground avoidance in flight.

Tell a little about your large helicopter - I am interested - we use one,
not so big, here in Namibia for photo shoots, and are working of a full
autopilot for it. Saw some very interesting heli's from a company in Germay,
capable of 15kg payload, twin turbine engine, etc. Very Nice indeed.

Regards all

Joe





-----Original Message-----
From: address@hidden
[mailto:address@hidden
] On Behalf Of Andrew S
Sent: Saturday, November 07, 2009 8:34 PM
To: address@hidden
Subject: Re: [Paparazzi-devel] distance measurement for landing.

Hi Joe.
i am interested in UWB radar too, could you tell me some words at greater
length?
We are working on 20 kg helicopter, and now selecting some of radio
altimeter..
Thanks in advance, Andrew

06.11.09, 21:23, "gisela.noci" <address@hidden>:

> Have tried this type of sensor - useless - does not work at all over
grass,
> nor over desert gravel/sand mix. Ok over tarmac runway, up to maybe
2meters
> - not really a reliable option at all - really needs good surface
> reflectivity
> I do autoland using ultrasonic sensors - 4 Murata MA40B8S transducers
pulsed
> in parallel with 55volts Peak to Peak, and 1 MA40B8R as receiver sensor,
in
> an own designed circuit. This works very well, giving 8 meter reliable
> detection over almost any bad terrain, except tall grass ( tall = more
than
> 500mm). Over Tarmac range is about 13meters. Uses a PIC processor. 
> You need LOTS of TX energy, hence 4 transducers hammered at the max
voltage.
> The LV-MAXSONAR EZ series are as useless - just not enough energy for
> surfaces with low reflectivity. 
>  I am working on a UWB radar ranger, which is really the answer - 2 watts
> power consumption will give range from 200mm to 1200meters, the hassle is
> antenna space needed - will not work on your average flying wing type A/C,
> but great on a 60 size trainer or similar.
> Don't waste your money on the Infra Red route...
> Joe
> -----Original Message-----
> From: address@hidden
>
[mailto:address@hidden
> ] On Behalf Of Chris
> Sent: Friday, November 06, 2009 7:42 PM
> To: address@hidden
> Subject: [Paparazzi-devel] distance measurement for landing.
> Hi.
> I would like to hear any opinions on those sensors:
> http://www.acroname.com/robotics/parts/R302-GP2Y0A700K0F.html
> and
> http://www.acroname.com/robotics/parts/R144-GP2Y0A02YK.html
> They look interesting and i am tempted to try and add them to the
paparazzi.
> Which one should you choose?
> Chris
> _______________________________________________
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