Altitude hold - how sensitive are you?

[UndCon]

I was thinking about Altitude hold...yesterday I flew with my Quadcopter that is equipped with a bmp085 and it was holding within 1.5 meter

Not bad but Ive had better day within 1 meter...


Now considering the bmp085 capabilities (from data sheet)

0,5m in ultra low power mode
0,25meter ultra high resolution mode
(down to 0,1m at best)

So what are we expecting?

BMP085 senses some difference in hPa (pressure)
MultiWii code adjusts motors accordingly (after applying filters?)
The result is bobbing up/down a bit

Say we have a good day - 0,25m and 1 step up means another 0,25m and Multiwii starts taking actions and drop RPM a bit. This causes your vessel to move to ground but to much and we go - 0,25m and before the motors gain RPM we drop yet another 0,25m -then we see a climb with increased RPM as a result

So if we move up/down 1 step from desired we still move within 0,75m at best.

What are your expectations to altitude hold?

Do you need more precision you can add a sonar for lower altitudes but higher up they are not as good and the percentage of fluctuation is not as bad.

Just some Ideas...

Cheers - UndCon

[mlebret]

Hello,

With 1m resolution when flying 50m above ground, I'm more than happy.

If I try to fly at 1m above ground, it's not so good.

When you look at the barograph in MultiWiiConfig, there is no chance to achieve better performance.

So, for me, below 5m I expect 25 cm resolution (sonar possible), above, I'm happy with the Baro.

Marc

[UndCon]

Yes that is close to my ideas as well - but there are lots of issues regarding barometer and I don't think pilots know what resolution their altimeter has and moan about it.

//UndCon