I had the same issues about pressure sensors. I solved it applying an IIR filter (Butterworth 3 order) always to the raw values from ADC, never to the post-processed data.
My problem with sensors started in Mentor because the motor vibrations (around 6000rpm ~ 133Hz), so
I have to sample at 266Hz minimum to avoid aliasing. With this, my signals from pressure sensors are really cleaned and the delay is about 0.01 seconds.
Thanks about your bachelor thesis, I will send you a link this afternoon (now I am at work) where download my MSc. Thesis (it is heavy due to the images, about 70MB). If somebody more is interested, I can post the link here in the mail list.
I will give a try to the AoA sensor based on pressure sensors (I think MPX7002 can do the work). Now I am learning about the STM32 micro, yesterday I had my first evaluation board from Olimex!, I built a gcc 4.6.0 compiler and flashed the board with a blinking led example with OpenOCD. So, it will take me time to get in used with the micro, rewriting firmware, assemble Lisa with Overo, assemble the new IMU... I hope in 3 months to be flying, at least with only telemetry.
Cheers
Héctor
On Thu, Jun 9, 2011 at 2:04 AM, Leandro Chelini <address@hidden> wrote:
@ Felix
The AoA Module needs changes in the estimator and there is a pitch
switch in the pitch loop of stabilization.
Maybe it needs a short description for the usage in the airframe.
If you create a branch only for this, witch I have write access to,
I can upload the code and modifications.
I think this is a part for the dev branch.
There are other useful modules that should be published. Like a
Flight Benchmark (error square sum) to optimizing the parameters.
But it needs time. In a few weeks I will have more time to publish
and describe the publishable code.
@ Hector
This sensor was the last thing we does to optimize the autonom
landing and the bungee start. So it isn't aerodynamic optimized.
With this AoA Thing on, the Mentor flies really crappy. But it does
it's work.
The "Flag" can also be built smaller.
I advise to take a sensor with bearing balls! (I took the M6-type
because I thought it has a metric thread)
I have bad experiences with pressure sensors. We have AMSYS pressure
sensors to measure the airspeed and we had to filter it hard to make
the data usable. In the case of the airspeed it isn't really bad if
the data comes 0.25 seconds delayed, but for a AoA sensor....
Maybe we took the wrong filter (PT1)
I can send you my Bachelor thesis, but it's in German. ?!?
The theses includes generally documentations about our autonomous
start and land algorithm. (sonar etc.)
Bruzzlee
Am 08.06.11 17:22, schrieb Hector Garcia de Marina:
Thank you very much Leandro.
Actually I am employing a Mentor Multiplex, and I found the
same hall effect sensor, but I am worried about
the size of your sensor and how it affects to the airfoil.
I have though in 2 dynamic pressure sensors attached
plus/minus 15º, with 0º at the mean airfoil reference. Hoping
that the pressure difference is proportional to AoA (small
angles approximation, minor than plus/minus20º AoA actually).
What do you think, have you tested this kind of idea before?
It seems mechanically simpler, but I do not know about what
performance I will obtain.
By the way, have you any documentation about your experiences
with Mentor? I can upload my master thesis applied to it as
well. Right now, I am sectioning the airfoil, and horizontal and
vertical tails, for applying them a CFD. Do you have experience
with this in Mentor?
Thanks in advance.
pd: you can check out this video with my navigation algorithm
running in a Mentor, it only shows attitude estimation http://www.youtube.com/watch?v=TRR4Jzz3ZjE&feature=related).
My HW is pretty similar to paparazzi classic, but employing
atmel at91sam7s256 instead LPC (DMA is a must for me), and I
added a SD card as well. Now I have changed to Lisa/L to start
with navigation algorithms based on camera vision, but it needs
some modifications for fitting my requirements.
Cheers.
On Wed, Jun 8, 2011 at 4:16 PM, Leandro
Chelini <address@hidden>
wrote: