MultiWii

Hi all,

The PID tuning docs have been pretty helpful for my new quad with MW2.4. However the altitude hold docs leave a lot to be desired.

I have set up my baro with a 10mm or so length of plastic tube (cut from a pen) and hotglued onto the top of the baro IC. There is a piece of dense foam stuck in the tube that I cut from a sheet with a large hole-punch for paper.

I get decent enough baro readings over a short period of time according to EZgui, but I can't get a decent performance for the altitude hold PID.

I have seen the other forum threads about the 2.4 altitude hold, including the thread about alt calculations and was hoping that somehow we could arrive at a better situation for those in need of help with alt hold.

I tried the process described at http://www.multiwii.com/wiki/index.php? ... titude_PID and with the PID at 0,0,2 my quad violently accelerates and gains 5-10M then plummets.

Since I have a reasonable but noisy altitude reading being displayed in the EZgui on my phone I would expect the PID tuning to be not-so-hard, but in fact I've had no success and a lot of frights, heavy landings, bouncing etc with a heavy beast of a video quad.

My gut feeling is that more smoothing of the baro would be better and the PID docs need the process rethinking!

Any help? I'm happy to update the wiki if someone gives me access and helps to arrive at a less scary PID tuning process.

Thanks,
Ed

Hi Ed,

I'm new to altitude hold myself and have only tried it once. I basically set the PID to be the same as my auto level settings and I briefly tested it outside close to the ground, it does fluctuate a bit but it's probably only by 3-4m so I'll need to try tuning a bit later though at no time did it drop or raise very quickly that would have caused me to panic.

How much does your reading fluctuate when on the ground?
I just taped on some black foam over the BMP185 baro.
Also when in baro mode I had Angle mode active (not sure if that makes any difference)

The method described in the link above works, but you must be prepared for some scary moments. I don't honestly think it is possible to set up alt hold without some scary moments... Once D is pretty well dialled in it behaves well.

My altitude reports very well, perhaps +-0.75m while left sat on the ground. I'm surprised by the performance of it.

I kept increasing D up to about 20 and at that point found it would hold altitude quite well for short periods... I now have to tune the P and I better to get longer term success. The weather hasn't been great here recently.

I have added to the PID tuning documents on the MultiWii wiki, please see the new links under PID heading here: http://www.multiwii.com/wiki/index.php? ... figuration

Please let me know if there is anything I have missed/got wrong/you would like to see improved or added...

I hope this information helps.
Thanks,
Ed