Hi,
I’m posting my configuration to hopefully remove some confusion / be helpful. This configuration has been ground tested and flown with ArduPlane 3.8.2.
Be very careful when changing the ARSPD_OFFSET and ARSPD_RATIO parameters. The values posed above work well for me but use caution when changing yours. Your sensor may require different values and getting them wrong can result in a stall / crash.
The MS5525 looks pretty good at measuring low airspeeds. This plot is heavily filtered diff. pressure, airspeed and gps speed from my first E-Flite Convergence hover test
This is a plot of airspeed North/East components (plus EKF wind estimate) vs. GPS speed components from flying slow circles while doing yaw tuning of my Convergence VTOL. I’d say this pitot system with the MS5525 is doing very well at measuring very low airspeeds, and that it should look even better at normal cruise speeds.
Yes, everybody is happy with the precision. Obviously better than the predecesor.
What needs fixing is the preflight calibration offset issue that has been reported and discused in lenght in this thread.
I have found that when you nose Up/down airspeed changes.
My setup Pixhawk2, MS5525 sesnor. After powering the pixhawk it zeros the airspeed. but when i nose up or dosn AS goes up to 2-3 m/s. Are you getting the same issue?
Make sure your sensor is shielded from sunlight. I’m seeing less than 1 m/sec orientation sensitivity in my Convergence as documented in my PR linked by Rolf above:
I suppose the orientation sensitivity might vary across sensors; there doesn’t seem to be any spec relating to that. Does the old airspeed sensor read accurately at such low airspeeds? What are the stall and cruise airspeeds for your airframe?
this new airspeed sensor very sensitive, even when i touch to plastic cover pressure changes.
I am thinking maybe AS changes when i rotate because of momentum something inside?
I flew with this airspeed, airplane doesnt handle altitude well, it lose altitude then climbe higer then lose altitude , i saw on blog other people also had this problem… are you getting any problem on flight?
The differential pressure at 8 m/sec is roughly 32 Pascals, at 2 m/sec it is about 2 Pascals, so the maximum effect of your observed sensitivity will be on the order of 0.5 m/sec near stall speed and 0.2 m/sec at cruise speed.
@pompecukor I haven’t seen any problems with preflight cal for the 3 MS5525s I’ve tested. I just boot up, uncover the pitot tube and fly. I’m flying my sbus1_hal PR branch on the Convergence, which is based on a recent version of master:
Ok, I just upgraded the firmware to 3.8.2, then checked the variance after rebooting, and with pitot tube covered it was reading 0.0 to 0.2 when powering the pixhawk only by USB. Then I took it out to the field for a test flight, and after powering up with the pitot tube covered, the variance was rapidly fluctuating from 0.0 - 5.5 m/s. I cycled the power a second time, and still the same variance, up to 5.5m/s, so I’m wondering if something else is causing this?
The old sensor was mounted in the same location as the MS5525, its an enclosed side bay, so no exposure to sunlight, only difference in this case is powering a Pixhawk 2.1 via USB or a Mauch Hall Sensor via 6S battery. The old sensor never varied more than 2.0m/s
Because of this, as I did before, I manually adjusted the offset value down until the airspeed varied from 0.0 - 0.2, and then did a quick test flight, and airpseed readings were very good, so I think until we can determine a fix for this, I’ll probably be best off disabling the self-calibration, and just use a fixed offset that I know works in the mean time.