On Tue, May 15, 2012 at 7:30 AM, Stuart MacIntosh
<address@hidden> wrote:
Hello and thank you to everyone who has helped this project become what
it is!
At the moment I'm planning how to best mate my airframe and a paparazzi
system, and I have a few questions.
I'm hoping to fly a blended wing body (Hobbyking ParkJet) and it's a
pretty fast wee thing, although it has a light wing loading and still
glides with a modest stall speed. Does the problem of drift in IMU's
become more apparent with an increase in velocity? (ie; is this thing
going to be too fast?)
You have to look at the curves of your accelerometers provided by the manufacture,
but the great issue here is the temperature.
The MEMS gyros can change their reading depending on the acceleration, not on
the velocity, but as before, the issue is the calibration over temperature.
Would thermopile-style attitude measurement be more suited to a faster
vehicle, and what are the dis- and advantages to these two attitude
measurement techniques?
If you have a clear sky, and you are not flying over water, it depends on
the bandwidth of your thermopile. Some users here can tell you that
this sensors depends highly on your weather, terrain, etc. The great
advantage is that it does not depend in any non-inertial effect.
An IMU can not measure the attitude by itself, it needs a fusion algorithm
such as DCM or Kalman Filter. The big issue here are the drifts, calibration, etc
(you have to calibrate your thermopile as well). The good news are that IMU
does not depend on the terrain or weather.
Should the IMU be located at the airframe's center-of-gravity?
(experience with race-car datalogging would suggest so) and if it cannot
be; is a correction factor needed?
Yes, you should, otherwise, your acceleration are not with respect the CoG, you should
remove them with the known distance to the CoG and the angular velocity.
This is a fun way to learn about control systems, navigation and flight
dynamics!
If this is your first experience flying (and moreover with UAVs) I do not recommend you
going so fast and start with a well-known trainer :P
Cheers,
Stuart.
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