Altitude Sensor

[LiveRock]

I got a bugging question in my mind...

Some Quads have altitude sensors, for example, the AR Drone 2.0.
How does it work if I am on the 2nd storey and the drone flew out of the window?

I mean, does it measure absolute altitiude from the sea level or relative altitude from the ground?

The height from the 2nd storey to the floor is different when the drone flew out of the window where the height is from the drone to the ground (maybe grass patch)

How does that work out?

[yovio]

There are 2 sensors that I knew use as altitude sensor, first is barometric/pressure sensor and second is sonar/ultrasonic sensor.

Barometric sensor measure the altitude based on the air pressure, so its reference is the sea level, this sensor is not very accurate nor has good resolution. The best resolution that I'm aware is around 10cm (MS5611-01BA03, use on ardupilot APM2). Barometric sensor can be affected by winds, the way we put our flight controller. The barometric pressure also unaware of the terrain bellow it.

Ultrasonic/sonar, the way it works is by sending ultrasonic wave that bounce back by the soil and measure the travel time. Based on the way it works, it will have limited maximum distance it can measure. This sensor usually very accurate. The drawback of this sensor is the measurement can be vary depends on the surface that use to bounce back the wave.

Cheers,

****

[sherchoo]

I got a bugging question in my mind...

Some Quads have altitude sensors, for example, the AR Drone 2.0.
How does it work if I am on the 2nd storey and the drone flew out of the window?

I mean, does it measure absolute altitiude from the sea level or relative altitude from the ground?

The height from the 2nd storey to the floor is different when the drone flew out of the window where the height is from the drone to the ground (maybe grass patch)

How does that work out?

Not sure which altitude sensors are you mentioning but for Spektrum telemetry, when the sensor is powered up, the level will display at ground level. That means if you powered the sensor on the 2nd floor, the actual ground level will display as -ve. Hope this helps

[elmosan]

Not sure which altitude sensors are you mentioning but for Spektrum telemetry, when the sensor is powered up, the level will display at ground level. That means if you powered the sensor on the 2nd floor, the actual ground level will display as -ve. Hope this helps

Correct. Spektrum sensor will calibrate to 0 when you initialize it. So if fly below u, the reading become negative. Assuming you fly on a 100m tall building, when you land ur drone on first floor the reading become -100m. The altitude is relative to u.

[LiveRock]

So, in the AR. Drone 2.0 video where the guy sits on the roof and let go the drone to fly out, there must be something really complex going on for the drone to fly out smoothly...

I wonder if there is a solution where barometric and ultrasonic sensors work in tantem with each other ...

[yovio]

Ardupilot APM2 can use both. Barometer is built in, and sonar is additional add on.

[mave]

My guess is that since the drone is AR Drone is flying out of the building, it is under the control of the user. And when it is under the control of the user, the altitude sensor will not be in effect. Even if it did, (my guess again) the altitude sensor will already be measuring the current altitude relative to the sea level, thus, flying out of a building makes no difference.

So, in the AR. Drone 2.0 video where the guy sits on the roof and let go the drone to fly out, there must be something really complex going on for the drone to fly out smoothly...

I wonder if there is a solution where barometric and ultrasonic sensors work in tantem with each other ...

[yovio]

I haven't seen the video, but I believe the altitude hold logic was not kick in in that matter, we don't really need altitude sensor for this purpose.

Altitude sensor required for scenario like Altitude hold (Holding the altitude even though there are external factor like wind trying to move up or down the copter) or Waypoint flight mode where we specifically ask the copter to fly to certain point at certain altitude.

[LiveRock]

Ok, got it.
That means the sensors come into play during altitute hold and not fully utilize during flight...