[revolt_randy]

Hi all, hope this isn't a stupid question, but how closely can a revo fly to the ground autonomously?

What I am looking for is a flight controller that can maintain an even altitude (say 10 feet) over the ground it flys. I've never used a revo before, or autonomous flight before. So I really don't know how autonomous flight works.

I know the revo has a barometer for altitude sensing, but how does that work? Are the readings from the sensor in the height above ground?

I've been playing with an arduino and an IMU, getting the data from the sensors and playing with it. I think I can write my own controller software at this point, but it would be a huge undertaking that I don't have the time for. So I am left wondering is there another solution to getting a quad-copter to follow the terrain?

Thanks for any help,
Randy

[Brian]

The barometer only reads (approximate) height above sea level.  It has no notion of ground level.  The only way of determining height above ground level (AGL) is adding to that very high-resolution elevation data, or another sensor (sonar or lidar).  Of course, if you're only talking 10 feet, then you also have the problem of obstacle avoidance.

I'm not sure if the current version of LP supports range sensors, but if not, it would be much easier to add that to LP than write your own.

[TheOtherCliff]

I wrote some code to add sonar altitude to LP, but had hardware problems.  It turns out that you need to buy the expensive maxbotix sensor since the cheap HC-SR04/5 has bad problems if the motors are running.

So there are 3 possibilities:
- sonar (not currently implemented)
- baro (works well, but only maintains fixed altitude, so no good in hilly area)
- GPS (currently fused with baro when using GPS modes, not repeatable, may vary several meters from day to day so waypoint flight must leave a large margin)

For a beginner just needing altitude help, use AltitudeVario (baro) thrust mode.

In the future, we may add sonar support which would help where the terrain is not level, but requires buying a $30 sensor.