MaxSonar EZ1 Sensor......Outdoors?

I would guess that means, don't get it wet. It is not conformally
coated or in anyways hardened against the weather. I don't think the
physics of anything changes outdoors. Of course temperature effects
the time of flight, so your readings will be off if the temperature is
different from room temp, but it's a minor correction. But I doubt
you'll be flying your helicopter anywhere or anytime that isn't as bad
for your brushless DC motor (assuming that's your power) as the sonar.

--
Randy M. Dumse
www.newmicros.com
Caution: Objects in mirror are more confused than they appear

Wind does. The Polaroid sensors are pretty good outdoors, and in fact
that's what they were designed for. But also they were designed for use
when the subject was typically 6+ feet away. If you're trying to detect
an object a couple inches or a couple feet away, the wind shouldn't
affect the readings all that much.

-- Gordon

Hi Gordon, any comment or idea on why? I thought about mentioning
wind, because I've heard it before, but decided I couldn't support an
objection. Speed of sound in air is roughly 1100 ft per second. A 30
mph wind would be 44 ft per second. Error should be minor in the
hundredths place. Humidity also bears on speed, as would altitude, but
I don't know if any of these would be very noticable. Ideas?

--
Randy M. Dumse
www.newmicros.com
Caution: Objects in mirror are more confused than they appear

Average air velocity is not a principal factor; turbulence (i.e. spatial
heterogenity)
is the main factor. Light speed is much more than sound speed, but turbulence is
a main
obstacle for optical observation/measurement too.

Nick

I don't know precisely why, but there are ultrasonic sensors for
measuring wind direction and velocity (quite accurate, too), so I assume
the change in transit times across the T/R pairs is appreciable enough
to make a difference, though whether it's enough to impact the
measurement beyond the natural error of the device I don't know. However
I do recall reading a white paper from Polaroid on how the frequency
sweep system employed in their large transducer design mitigated the
effects of wind. They were quite proud of it in fact.

I have also seen a couple of people note spikes in the output when using
the Ping outdoors in windy and/or wet weather. Caught some of it on
discussion boards related to measuring snow depth. Can't seem to find
them now...

-- Gordon

These work by measuring the transit time from A to B, and orthogonally
from C to D, and adjusting for temperature. The sonar distance sensors
OTOH measure a reflection A-B-A, where the effect of wind in the forward
path is cancelled by the same wind on the reverse path.

Clifford Heath.

That doesn't make sense. If you have a wind that is perpendicular to the
direction of the sound wave, the return beam will not somehow find its
way back along the same path. Its return will be sheared the same amount
and in the same direction *away* from the original signal source.

-- Gordon

Yes, but if you do the sums, comparing with the speed of sound at 342m/s,
you have to get a *very* strong wind to get much inaccuracy. I guess if
a few percent matters you might care, but for navigation, it's negligible.

Just to put numbers to this, a 60 knot wind is about 30m/s. arctan(30/342)
is a 5 degree slip angle, and 1-cos(5 degrees) is 0.0038 - less than half
a percent of error. In that much wind you'd have trouble hearing your ping
anyhow.

Clifford.

I see your point now, but I don't think it's just time-of-flight that
matters here. I brought up the ultrasonic wind sensors because clearly
these devices are accurate enough to detect changes in wind
direction/speed just by comparing differences across a pair of
tranmitters/receivers. Beyond that though it's somethiong of comparing
apples to oranges. I think one thing to concentrate on is the "mirage"
effect and how air turbulence can distort the reading.

But probably more critical is that an ultrasonic receiver is effectively
a microphone (though admittedly with somewhat different characteristics
than a 20Hz-20kHz mic). Anyone who has used a microphone outdoors in the
wind knows about the unpleasant "pops" of sound that occur when the air
hits against the element. If a reading takes place right at the time of
a pop it'll be an invalid measurement for sure.

-- Gordon

and from B to A.
after which these 2 measurements are subtracted ;-)

Stef

  The low cost 40khz piece-o-electric

 have very high Q and ring forever

 if you take them outside where those

 frequencies are much higher .

  Thats why Poloroid  created

 a higher voltage "electrostatic"

 method ( opposed to Piezo) ,

 which has not the Q

 or "storage" of energy , thus they

 can quickly stop , after sending

 out a pulse .  They stop so quick ,

 one can measure very short distances .

 The best use for P' is to chase away

 mosquitos .

  Im doin mcu's , just got lots of Ninetendo

 DS lites and ARM7 mcus .  Ill be cutting

 down the size of s/w , handing out a free

 Op System soon .

  Ill test the Op Codes and other stuff ,

 like USB , on the ARM7 mcus and

 then write a new Op Sys for the NDS lites.

   I will tunnel RS232 and even USB and

 EtherNet and the ARM loader and CAPS

 and Angel and IDE's and .....

  A new Op Sys , without text input !







On Feb 16, 8:41 am, w...@drexel.edu wrote:

I have heard reports of the MaxSonar-EZ1 sensor working very well for
use in flight both (blimp and helicopter) use.  At least one small
model helicopter company compared the outputs from the MaxSonar-EZ1 to
other sensors, and then selected the MaxSonar-EZ1.

The MaxSonar-EZ1 Calibration Cycle is very useful here!
One thing the helicopter folks did was wait to take the first reading
until in flight, so the calibration cycle would adjust for conditions
(even ambient wind noise).  They reported that the readings were
useable and stable, even during flight.

(PS. Unless you build a special housing, don't fly in the rain.)

Bob Gross
CEO MaxBotix Inc.
www.maxbotix.com