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| From: | Luke Ionno |
| Subject: | Re: [Paparazzi-devel] Barometer/Altitude Estimate Drift |
| Date: | Fri, 7 Mar 2014 19:09:03 -0500 |
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Kadir, I just did a test of your approach, I powered up the board, and let it sit for half an hour, before doing some test hops. Sure enough, it’s spot-on, no drift I can see. Did a bit of poking, and it appears that this is a sort of known problem with the MS5611, there’s some discussion over on DIY Drones, that describes much the same problem (and unfortunately, the workaround is pretty much the same too, power it up and wait a while. http://diydrones.com/profiles/blogs/baro-drift-and-how-i-got-round-it) Based on this, I think I’ll have to bite the bullet, and implement sonar for my indoor work. -Luke From: address@hidden [mailto:address@hidden On Behalf Of Luke Ionno Kadir, Thanks, glad to hear I’m not the only one. That does sound very similar to what I’m experiencing. I just flew outside for ~12 minutes, and over the first 3-6 minutes of the flight, I lost about 3m, out of 6m AGL… Bumped it up by 3m, and then as you say, it stayed put pretty well. I figured that most people are probably flying high enough so that the loss of 3m or so isn’t significant, but I’m doing some flying indoors, where 2-3m is not an insignificant percentage of my working height. -Luke From: address@hidden [mailto:address@hidden] On Behalf Of Kadir ÇIMENCI Hi Luke, I have a similar drift problem on altitude, not exactly the one you have but when i leave the board on my desk with powered on {motors off/ only the board powered} the baro raw and consequently ins z values are starting to climb up slowly{always upside as you said}. I measure 2meters of drift in 15-20minutes. I omit this drift because im flying outside with altitudes of 40-50 meters :). One weak explanation in my mind is the heating the sensor itself, and the components next to it , mpu6000 or magnetometer etc., because i made a test when i encounter with this problem. I powered on the board and wait 20 minutes approximately and there was a drift of 2 meters approximately and then realign the vertical ins and the altitude did not changed a lot . I interpreted this result, as the sensor and the peripheral components had reached a stable temperature and there is no pressure change in environment due to heat changes..{It may be a little wacky :) } Kadir 2014-03-08 0:22 GMT+02:00 Luke Ionno <address@hidden>: 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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