I have to estimate the pitch rate and the roll rate of a vehicle, from measured accelerations. I have many three axial accelerometers. How can i accomplish it?
For pitch, you might place an acc. in the nose, at the center of mass, and in the tail, and analyze on that basis. Similarly, for roll an acc. in each wing tip and one at the cm might be worth considering. Of course you need your aircraft's dimensions in order to translate linear accelerations into angular velocities, etc.
i have to measuring these quantities in a vehicle for measuring the roll rate and pitch rate inducted from the road roughness. Moreover i don't know where the centre of mass is placed, and also it isn't possibile to place accelerometer in that point. Does your methodology work the same one?
If these are "axial" accelerometers, than placement doesn't matter, as long as you get the "axis" of the accelertometers aligned with the desired axis, pitch, roll, yaw. You wouldn't need to calculate anything, just convert the outputs of the "axial" accelerometers into a rate such as radians / second. Radio control helicopter generally use silicon based "gyros" which include axial accelerometers in the form of a vibrating component that varies electrical output based on rate of rotation.
For an accelerating automobile, the torque in the propeller shaft (into the differential) creates an axial pitch (torque). For a propeller plane, the prop torque (power/radians per sec) may create a pitch also. Bob S
thank you. I have understand. A question, if i can't align the accelerometers with the desired axis, how can measure the pitch rate? I ask you this only for better comprehension of the vehicle dynamic
If the 3 accelerometers are mutually orthogonal, then a simple mathematical coordinate system rotation of axes (Euler angles) http://en.wikipedia.org/wiki/Euler_angles will align the accelerometer readout with the vehicle axes. Bob S
If you can't align them, but you have 3, then you can do a conversion as mentioned in previous post, but you'd need to accurately know the axis angle offsets, which would probably be just as difficult as aligning them. If you can setup or buy a 3 orthogonal axis cluster, then you could mount the cluster, then accelerate and brake, adjusting the cluster until you just get a readout for pitch. Yaw and roll would be more difficult to separate, perhaps pushing on the car from the side. You could use a level to make sure the cluster was vertically and horizontally aligned, but the yaw axis would still be an issue.
I need some information from you guys. I have readings from acceleration sensors i.e. Acceleration along X-axis, Y-axis and Z-axis. I want to find the Pitch and roll angle from the above data. Is it possible to find the Pitch and roll data from accleration data. Regards waiting for your kind and early reply
Try to take a look at pag 193 of this book. http://elib.tu-darmstadt.de/tocs/209699132.pdf You can read it from google books.
Dear Actually this book is not frequently available. Can you upload those equation which help for combine angular and translational accelerations?
take a look here: http://books.google.com/books?id=tv...&resnum=1&ved=0CC8Q6AEwAA#v=onepage&q&f=false however are normal equation of classical mechanics...