Aspd bad values #3043
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The manual for ASS is very bad, but it mentions a "Reset button" and it supposedly does a "user calibration". @janekx do you know how the user calibration works? And just to confirm what you are saying above: when the car was going 50 km/h you got 32 mph and 21 km/h readings on the radio (depending on the unit that is setup for the sensor). |
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Yes I know calibration procedure, it is simple reset, no wind and pressing will zero the device. |
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just a question, should an air speed work as expected near ground?! you mentioned a car... |
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Please be sure i not measure my air-conditioning |
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What griebd means that air speed sensor should be in clean air. In your case you should put it on a long pole and stick it out of the car at least 1 meter if not more. |
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about 0.7m off the car diagonaly up and right. There is no much air mass around car in lower speeds, it grows how does car goes faster. |
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By the way the test was done based on the client info that it measure too low, because we were not able to measure the plane well, we choose car as some kind of reference. |
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@janekx do you have a log file of the testing, it might give us some additional clues. |
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No, I have logged but forget to check at sensor log option :( I can make the log, we spend about hour to measure it. It measure well but wrong values. |
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Some findings:
Perhaps we should make a special build for @janekx with sport logging active to see what kind of data sensor actually sends. @janekx would you be able do do another test, it does not have to be in a car, the wind simulation with a fan will do. |
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Yes it is good idea, i can test all ASS types and N2 as well have here. I can log the serial smartpor to terminal as well but if will make the raw smartport log for sd and logfile of data there can be same timestap for better analysis |
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@janekx for which radio should we prepare the custom firmware? X9E, Taranis or Taranis Plus? |
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X9E and going to make some testbed with fans |
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I was looking around for certified blower, my wifes hair drier have no speed certificate and all other fans I have here are super silend so slow... |
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No need for super accurate speed reading now, we just want to see the data stream at several speeds. Special OpenTX version with S-PORT logging for X9E is available here: http://www.filedropper.com/opentx-215-x9e-sportlog Just for reference the file above was compiled with: Instructions:
Thanks for you effort. |
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Here you have it http://rcstudio.cz/LOGS.zip |
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@janekx I analyzed your data, it all seems perfectly OK, no anomalies. How did the Aspd- and Aspd+ behave in this tests with this special firmware? I can not say nothing about the speed accuracy, but otherwise the data is as expected. Examples of parsed packets: |
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I think I had filter enabled that stay from setting before. No issues about + and - but what about final displayed speed? If you read 31m/s why the display shows abour 20? I had selected kmh so log says kmh values. |
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You had |
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Yes auto offset and filter but the values was same as we tested in car day before. So we test filter because strange numbers and auto offset. |
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OK again, Max speed I saw is 25 kmh what you will see from raw data ? Idle ----- speed 1 --------- speed 2 max speed 2 I see 25kmh |
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So far I am not seeing any problem with the air speed measurement with the custom firmware. @janekx would it be possible to test the sensor in the car again with the custom firmware? The log files might tell us something at higher air speeds. Your sport.txt gives this (looks perfectly ok): |
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I just measured values with an N2 airspeed sensor and an OXS GPS on a car (about 1m in front and above the car) that are about 2x the actual values for both the airspeed and the GPS ground speed. The two readings seem to correlate, just both out by about 2x. I am using OpenTx 2.1.7, I had kmh set for units on both Gspd and Aspd. My Taranis B model was set to metric. I believe I was getting correct speeds from a FrSky GPS in an earlier version of OpenTx 2.1+, but the N2 airspeed readings were incorrect then because I didn't have the 47.1 ratio. Should I not use the 47.1 correction factor in 2.1.7? Is the GPS speed problem with OXS or OpenTx? Thanks! |
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GPS speed sent by sensor is in knots isn't it? |
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@kcaldwel There was a change in the unit. Originally the FrSky specification had km/h for the Air speed unit. After the testing we found out that it was wrong and that the actual unit is knots. So we changed it in 2.1.7. |
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If I understand correctly, I no longer need the 47.1 ratio for the N2 airspeed sensor. And I need to re-flash my OXS to send knots, not kmh. Thanks! |
Reopening this as following the RCG discussion yesterday I asked Adela again... and FrSky assure me 100% that their airspeed sensor supplies km/h, not knots. Whoever did the measurement could have forgotten that the radio was already applying a conversion... |
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This look like immortal bug. Can you please ad the link on discussion? |
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I just ran a quick first try with my manometer airspeed calibration set-up and the FrSky ASS-70 using OpenTX 2.1.7.. It is a windy day, and the static pressure in the building was fluctuating. That makes the lower speed readings a bit unreliable, but as a test I think it worked OK. I have a couple of improvements to make to get consistent readings as well. I had the Tx telemetry set to knots. I believe the FrSky -70 is sending knots, and reads about 5% low across the range. I will hopefully test the N2 airspeed sensor soon.
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I got a quick run in on the N2 airspeed. Again, we have a big windstorm at the moment which is making the static pressure in the building unreliable, so the results aren't as solid as they should be. I am using Richard Johnson's (full-size sailplane test guru) method of calibrating airspeed against a known pressure in a manometer. It should be accurate, but a calm day would help! The pressure changes are very small, especially at the lower airspeed values. The N2 sensor I have has an error in slope the other direction from the FrSky. It sends one tenth knots, while the ASS-70 only reads whole knots. There could be quite a bit of variation in the individual sensor response to pressure, so it is quite possible other sensors of the same make will show completely different errors. I haven't checked the spec sheets for the +/- to see if these results are within the sensor variations, or perhaps some correction could be done in the firmware. These results are again on OTx 2.1.7, telemetry in knots, no ratio or offset. The FrSky sensor was through a XR4 Rx, the N2 was through a XR8, but hopefully that doesn't make any difference.
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The sensor sample count is low so nothing substantial can be concluded yet, but it looks like both sensors are reporting speed in knots as predicted and measured earlier by @janekx The code is already up to date with that, only FrSky's SPORT specification is still wrong. |
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@projectkk2glider yes I think so. There was detailed research in this area and direct communication with FrSky agreed the knots before and tests proove it |
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The thing is their doc still mentions km/h, and when I asked them last week I was told it was "km/h for sure"... |
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Yes, but we discuss it in mails with Adela and other engeneer and was confirmed that kmh are wrong in protocol datasheet. |
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Well again Adela and their engineer just told me it was definitely km/h... which is why I reopened so that we recheck to be sure. Looks like knots are right indeed. |
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The manometer method I am using is the same method they use to calibrate full-size aircraft airspeed indicators with, except I am using distilled water (density corrected for temperature) instead of mercury to increase the low end sensitivity as Richard Johnson did in his set-up. It is calibrated to the ICAO Standard Atmosphere conditions. It should be the best method to actually calibrate an airspeed sensor. I still have a lot of wind here today, so there is no point in testing. I will have an oXs sensor ready to test shortly. There is no way the FrSky ASS-70 is sending kmh, it is even 5% low for knots. 5% error for the low precision version of an uncalibrated sensor is reasonably good. The N2 is closer to sending mph than knots: 1.15mph/knot; the N2 is sending 12% high. |
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@kilrah any progress? I think we can close this issue. |
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I got from FrSky some custom ASS firmware but finaly we switch back to factory and it is ok |
I think we got in trouble with Aspd measure. Tested 2.1.3 and 2.1.5 public
Used ASS-70 and ASS-100 both same issue.
Actual / measured in kmh
30 / 12
50 / 21
80 / 33
100 / 42
Actual / mesured in mph
30 / 19
50 / 32
60 / 40
From this I see that there is some calculation issue. In fact I cant keep car running exact same speed there can be 5-10% fluctuation, but this is too much :)
in kmh there is 2.5 multilier to got actual speed
in mph is 1.6 multiplier
When we not use the filter we got the bas screens values as well, the Aspd+ and - stop changing and show absolute bad values with bad signs, here is the photo, when we used filter never come back.
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