I’m having serious problems with airspeed sensors. I’m running ardupilot 3.6 on three fixed wing build and my airspeed sensors are completely out of sync. Before every flight I before a preflight calibration, but the one plane will think its flying at 18 m/s when it is actually flying around 11 m/s. Whenever I start up the planes, the initial airspeed idles around 9m/s (even indoors) and after the calibration will idle around 2-3 m/s. I’ve bought three replacement airspeed sensors and see the same behavior. What could be causing this problem?
Here’s some ideas:
- Do you have the analog or digital airspeed sensors? Note that they connect to different Pixhawk ports.
- Are you covering the pitot tube at boot? Make sure to prevent airflow on the probe, but do not increase it’s pressure while it’s covered.
- An idle around 2-3m/s is common, I get concerned if I see many 4’s or any 5’s. Of course when you blow on it, you should see it rise.
Digital airspeed sensors
This is common across all the airspeed sensors. It is the spikes up to 9 m/s and the large error of up to 7 m/s while in the error that causes the problem. I’m thinking there is EMI with the airspeed sensor, and although all my wires are twisted I’m still getting the error.
I don’t have additional ideas. Someone else?
The sensors change their output as they warm up, so some time allowed after switch on is required. We do a calibration while using a cover just before flight.
The I2C protocol is not good for remote sensors. In particular, having the SCL and SDA wires beside each other over long cables to the remote sensor is not good. If you are using a ribbon cable place the SCL and SDA wires on the opposite edges of the cable with the positive and ground wires in the centre. If you are still having trouble, try running the air presssure tubes all the way into the fuselage just as full size aircraft do.
Be aware that the pitot tube has to stick right out into the airstream.
I only have one digital airspeed sensor that came installed on a 3DR Aero, I have 8 analog sensors. The digital is the only one that gives me trouble. The other day it showed 14m/s on the ground. I did the Preflight Calibration several times and it would drop to 5 m/s, then climb back up to the teens. I decided to cancel the flight, but as I was packing up I noticed it dropped down to 2-3m/s. I made a test flight which went well, but on the graph it shows a very noisy signal, varying about 3 m/s.
I like my old analog sensors, they work great.