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Airspeed sensor noise problems on Large Quadplane

vtol
quadplane
airspeed-sensor
cube

(Lau Yan Han) #1

Hello all,

Recently, my team tested a large quadplane model, and ran a satisfactory flight in AUTOTUNE mode. However, I noticed from the log analysis that there are some noise issues with our airspeed sensor; see the screenshot from our log below:

From the log, the airspeed gets frequent sudden spikes to zero throughout its flight. Also, the NKF4.SVT values frequently exceed 1. According to this link the EKF will reject the airspeed data when this parameter goes above 1; that means that my airspeed sensor’s readings are not being used through many parts of the flight due to the noise issues.

Right now, we don’t experience adverse issues as we are flying under RC control. However, this is still a cause for concern when we perform AUTO flights in the future. What I am curious to know is:

  1. What problems will these airspeed noise and EKF rejection behaviour give when we perform autonomous flights?
  2. How do we go about reducing the airspeed noise?

Below I have attached the flight log, param file, as well as other info that may be handy:

  • Our airspeed sensor and pitot tube are mounted along the right wing, shown in this picture:

Any help will be really welcome!


(Ulf) #2

too long i2c wires? use shielded wires, or better use long pressure tubes.
also the sensor is very close to one of the quadmotors.


(Lau Yan Han) #3

Thanks for the reply! Just to give a bit more info: We avoided the need for excessively long i2c wires by using a I2C - Cat6 extender system with the following connectors: https://learn.sparkfun.com/tutorials/qwiic-differential-i2c-bus-extender-pca9615-hookup-guide?_ga=2.53437102.702448980.1536918502-1594996185.1535701754

Below is a photo of airspeed sensor setup before we integrated it into the aircraft, note the I2C - Cat6 connection that we used to connect the airspeed sensor to the Cube:

NemoAvionics

(Sorry for the poor resolution, this was the best photo we could get from the preliminary setup!)

Nevertheless, our airspeed sensor is indeed poorly positioned, and the pitot tube is the stock tube that came with the MS4525DO. We are trying to look into ways to better position the sensor and source for longer tubes, but I don’t foresee the work being completed before our next test flight. Hence I am curious to find out if there are any adverse consequences if I fly with this kind of noise during an autonomous flight.


(tridge) #4

It looks like a cabling issue. The key thing to look at is the ARSP.Temp reading, which is the airspeed temperature:


The good news is it shows the issue even when you are on the ground. I suggest you put a good logic analyser (eg. Saleae Pro) on the I2C pins and see if you can spot what is happening. Also try without the differential extender.
Cheers, Tridge


(tridge) #5

It will probably fly OK, but it is risky. I suggest you fly with ARSP_USE=0, which means it will log the airspeed sensor but not use it. It will use a synthetic airspeed estimate instead. Make sure you set TRIM_THROTTLE to a value a bit above what you expect to be needed in cruise flight (ie. at least 50 on your airframe).
btw, your ARSPD_FBW_MIN looks a bit low for that airframe. Are you sure it stalls at below 13m/s ?
Also, your vibration levels are far too high:


you need to add some good isolation foam below the cube (the internal isolation of the cube is not suited to the frequencies in your airframe). This is causing significant pitch estimation errors in flight.
Cheers, Tridge


(Lau Yan Han) #6

Thanks @tridge ! Airspeed sensor temperature was not something I had thought to look at previously, and my understanding of I2C is pretty limited. How does the airspeed temperature affect the performance of the sensor?

Nope, stall speed is definitely higher than that, will need to sort this out when we tune our TECS.

Thanks again, and will check in when I have updates!


(tridge) #7

it doesn’t (or at least not much)
The reason the temperature log is useful is it is unaffected by the pitot setup. So if the temperature is going crazy then it is confirmation the issue is with the i2c link, and not with the physical setup of the pitot.
I know that from the airspeed log that was already very likely, but I usually check the temperature to be sure.
Cheers, Tridge