Re: [Paparazzi-devel] Barometer/Altitude Estimate Drift

[Luke Ionno]

Sergey,

Gotcha, so no GPS correction of barometer drift...  This agrees with my most 
recent tests (been a busy day so far)...  I enabled ATT_Z_HOLD, so I could test 
the altitude drift situation with/without GPS, while plotting the raw barometer 
data.  

I flew two back-to-back flights, one with GPS, one without, each 10 minutes 
long.  Over the first 5-7 minutes, the altitude hold would look spot-on (within 
reason, probably +/- 0.5m drift), then over the next 3-5 minutes, it would 
settle in a fairly linear fashion, ending with it sitting on the ground, 2m 
below the setpoint.  The raw barometer plot for the 10 minutes of flight was a 
dead straight line for both tests, indicating that the aircraft held altitude 
WRT the barometer reading very nicely...  This is after preheats, etc.

I agree that atmospheric pressure variations would also disturb the altitude 
estimate, but given the relatively short time (and consistent direction) the 
drift is occurring, I don't think that's what I'm bumping into here. 

In any case, I've got a sonar sensor on order, so we'll see how that plays out. 
 

-Luke

-----Original Message-----
From: address@hidden [mailto:address@hidden On Behalf Of Sergey Krukowski
Sent: Saturday, March 08, 2014 12:00 PM
To: Paparazzi UAV devel list
Subject: Re: [Paparazzi-devel] Barometer/Altitude Estimate Drift

Hi Luke!

I also faced the problem. An outside pressure drift should also be taken into 
account there. So the resulting difference could actually be of both signs.
Currently in the ins subsystem there is possible to correct the altitude with 
sonar readings.
I've already implemented in my own sources an extra functionality to correct 
the altitude with GPS altitude as well. But according to brief flight tests 
it's also going to be about +/-1m of final altitude difference.

Best Regards,
Sergey

> 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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