Re: [Paparazzi-devel] Vibration probelm can be solved by useing, the acceleration sensor R9500M from MEMSIC

[Hector Garcia de Marina]

Dear Heinrich,

If the filter has a 'non-software' (or whichever) filter, then this is not imply necessarily that you will not suffer of aliasing.

This filter inside the sensors has a stop band at X Herz. If your vibrations have frequencies bigger than X/2, you will have aliasing.

So the key is to characterize your vibrations first, from here you can determine your sample rating (bandwidth), if you want to have a really precise measurement of the gravity (at 0 Hz, it is a constant signal).

Probably, this sensor has a really nice high bandwidth, and they can filter the vibrations (lets say over 50Hz?) without suffering of aliasing :P, and therefore you can measure the gravity vector quite nicely.

 

On Fri, May 31, 2013 at 11:55 AM, Prof. Dr.-Ing. Heinrich Warmers <address@hidden> wrote:

Dear Hetor
for MEMS with spring it is right,.
but the Principe is temperature flow of air?
an the bandwidth is low. Therefore no aliasing  occurs
since the sensor has the filter inside.
Please look at the video on the  mikrokopter page.
There got  a much better result then spring mass sensors.
Heinrich

Hector Garcia de Marina schrieb:

Vibrations in the end are accelerations (actually they are sinusoidals).

An accelerometer measures de vibration (because it is a physical effect), no matter how bad or good the accelerometer is.

If your accelerometer has a nice bandwidth, you can filter the vibrations nicely, but this is post processing (i.e. software or mechanics such as dumpers).

If your accelerometer does not have enough bandwidth. You will have aliasing, and that means that your low frequency measurements are corrupted, i.e. the measurement of your gravity vector is corrupted.

So, I do not see clearly the advantage of using this accelerometer. They claim something that can be done with 'standard' MEMS.

On 31 May 2013 08:46, "Prof. Dr.-Ing. Heinrich Warmers" <address@hidden> wrote:

Hi Chirs,
please look here:
https://www.mikrocontroller.com/index.php?main_page=product_info&cPath=69&products_id=773&zenid=eac7054440d993bc29899e8b5e4ae702
In a muitikopter this sensor is used for high quality altitude control.
Heinrich

Chris schrieb:

Any link?
I am trying to find it but it looks like it is not available inside microkopter's site.
Thank you for your help Heinrich.
Chris

On 05/29/2013 07:00 PM, address@hidden wrote:

Hi,
by using the vibration sensor without a mass and spring  (temperature
flow principle) R9500M
the vibration problem can be solved.
The idea is to use this 1.5g analogue sensor  for correction of the bias
of the  gyros sensor.
Since the sensor is fast  and not affected by vibration it seems  to be
a good solution for new autopilots.
For the old autopilots  you can  get  a small pcb (29Euros)  from the
mikrokopter shop.

_______________________________________________
Paparazzi-devel mailing list
address@hidden
https://lists.nongnu.org/mailman/listinfo/paparazzi-devel

_______________________________________________
Paparazzi-devel mailing list
address@hidden
https://lists.nongnu.org/mailman/listinfo/paparazzi-devel

_______________________________________________
Paparazzi-devel mailing list
address@hidden
https://lists.nongnu.org/mailman/listinfo/paparazzi-devel
  

_______________________________________________
Paparazzi-devel mailing list
address@hidden
https://lists.nongnu.org/mailman/listinfo/paparazzi-devel

--

Héctor

Webpage: http://mathtronics.wordpress.com/