One clarification, using the “no_type” INS, exactly what sensor readings
are fused into the altitude estimate? Is the GPS used only to zero out
the barometers during initialization, or does it remain an active part
of the filter input throughout operation?
-Luke
From: address@hidden
[mailto:address@hidden On
Behalf Of Luke Ionno
Sent: Saturday, March 08, 2014 9:36 AM
To: 'Paparazzi UAV devel list'
Subject: Re: [Paparazzi-devel] Barometer/Altitude Estimate Drift
Thanks for the information! I’ve actually got a pair of LISA/M 2.0s,
and having done some multi-ship work with them, I know they both
experience the downward drift, though come to think of it, one of them
may have a bit less drift than the other.
I just did a flight test with a 1 hr. ‘preheat’, and it seemed to help,
but in the end, I still had ~3m downward drift in the estimate over an
18 minute flight. During the preheat, the altitude estimate was varying
by 2+ meters, so if the motor noise is contributing, it’s not changing
things that much. (I’ve already got a sunshade on the sensor.)
In the end, I think Kadir is right, sonar is the way to go for my
application. When I’m indoors, I’m flying over a hard, flat floor,
which should provide a good strong return on the sonar pings...
Outdoors, I’ll just leave 3-4m of altitude margin, and accept the drift.
-Luke
From: address@hidden
[mailto:address@hidden On
Behalf Of Prof. Dr.-Ing. Heinrich Warmers
Sent: Saturday, March 08, 2014 7:20 AM
To: Paparazzi UAV devel list
Subject: Re: [Paparazzi-devel] Barometer/Altitude Estimate Drift
Hi Iomo,
we had also a drift problem with this sensor.
After we change the sensor we had no Problems. So the sensor was defect.
With the Bosch BPM085 i had many problems after soldering and head up.
About 30% of the sensor i had to change.
For pressure sensors on muticopters you can apply some foam if you
have problems with the Propellor wind.
This also help for light effects.
Regards
Heinrich
Luke Ionno schrieb:
Hello all,
I need a reality check on exactly how good (or bad) an altitude estimate
I should be expecting from the V5.0.3 rotary wing branch, using the
‘no_type’ INS, and a LISA/M 2.0, with the MS5611 barometer on an Aspirin
2.2 IMU board.
Right now, in a completely static indoor environment (no fans, open
windows, etc.) I’m seeing upwards of 2 meters of altitude estimate
drift (always upwards, I might add). The attached files Static Test
1.jpg and Static Test 2.jpg show roughly 20 minutes of static (motors
off) testing; I reset the vertical filter after the end of Static Test
1.jpg, but didn’t cycle power. Every minute or so, I’d lift the quad up
to the ceiling (~2.25 meters up), hold it there for ~10 seconds, and
then set it back down. Over the first 10 minutes, there’s approximately
2.5m of upwards altitude drift, and then another 1.75m over the next 10
minutes. The overall magnitude of the floor-to-ceiling step input seems
consistent, but the absolute altitude estimate drifts quite a bit.
I then took 10 minutes of raw barometer readings, which showed a similar
trend, as shown in Static Raw Baro.jpg. At the end, I threw in a couple
floor-ceiling cycles, just to get an estimate of how much drift I was
seeing. (If I were using the raw barometer readings to estimate
altitude, the drift over 10 minutes would have been ~1 meter.) Of
course, that’s all with motors off; I did an outdoor tethered-hover
test, with a 2m tether, in manual flight mode, recording the raw
barometer readings, and got the plot shown in
Tethered_Hover_Raw_Baro.jpg; note that at each landing event, the
barometer reading has drifted by ~2m in a matter of 60 seconds. The
barometer is well clear of the ESCs and other potential heat sources,
and I allow it to acclimate to the outside temperature before flying.
I’ve flown a number of NAV flights with this setup, and they’re quite
consistent with the static plots and tethered tests; I’ll start out say,
2-3m AGL, and over a minute or so, it’ll drift downwards by a couple
meters, until it ends up sitting on the ground with the motors idling.
(The vertical loops are well-tuned, it’s that the altitude estimate
itself develops errors). I can bump it up a couple meters, and then
it’ll hold for somewhat longer, but it general trends downwards over the
course of a 15-20 minute flight by ~4m or so. As noted before, the
aircraft altitude estimate always up, never down.
So, are the various drifts shown above normal for a GPS + barometer
setup? Is a +/- 2m altitude estimate simply too much to ask of the
system, or do I need to start hunting down sources of vibration/noise,
etc.? Is anybody else experiencing this sort of behavior?
Thanks!
Regards,
-Luke
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