Servers by jDrones

New Airspeed sensor (MS5525) for ArduPlane 3.8

(Samuel Dudley) #74

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.

Note: The sensor is connected directly to the I2C port labeled I2C 2 on the carrier board.

ARSPD_AUTOCAL    0.000000
ARSPD_BUS        0.00000
ARSPD_OFFSET     55.642334
ARSPD_PIN        15.000000
ARSPD_RATIO      1.627000
ARSPD_SKIP_CAL   1.000000
ARSPD_TYPE       3.000000
ARSPD_USE        1.000000

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.


(Mark Whitehorn) #75

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

(Mark Whitehorn) #76

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.

(Pompe Cukor) #77

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.

(Mark Whitehorn) #78

There’s no “offset issue” apparent in my testing; do you see one in my plots?

(Mark Whitehorn) #79

First flight of my E-Flite Convergence with the mRo MS5525 airspeed sensor.
@Jordi looks great!

parameter values:

ARSPD_RATIO      1.993600
ARSPD_SKIP_CAL   0.000000
ARSPD_TYPE       3.000000
ARSPD_USE        1.000000

Mini Talon QuadPlane Conversion
(Rolf) #80

The noise is much better than that of the 4525DO chip:

But i also noticed the sensitivity to device orientation.

Regards Rolf

(Artem Skorsky) #81


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?

(Mark Whitehorn) #82

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:

(Artem Skorsky) #83

I have covered the sensor, but still AS changes when i nose Up the Cube. i tried with old airspeed sensor, works perfectly

(Mark Whitehorn) #84

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?

(Artem Skorsky) #85

old airspeed sensor MS 4525 works accurately. stall speed around 8 m/s cruise 12m/s

(Artem Skorsky) #86

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?

(Mark Whitehorn) #87

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.

That’s assuming my calculations are correct. The relevant code is here:

(Jordi Muñoz B ) #88

Great, great news! Thanks for the report. Let me know if you need anything. :wink:

(Mark Whitehorn) #90

(Rjiun Raj K) #91

It’s great.
I hope i can purchase one. i wish to.

(Pompe Cukor) #92

So you did not need to use any offset on your own?

I just cannot get min to zero out.
It is jumping 1-8km/h

My biggest concern is still if the original issue is fixed. That is if pre-flight calibration messes it up or not.

(Mark Whitehorn) #93

@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:

(223Wylde) #94

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.