RC PLANE ROLL STABLIZATION

[faraz101]

rc plane accelerometer

i want to build the roll stablization device for my rc plane.i want to use the accelerometer adxl202 coz in datasheet i found that it can used as a tilt sensor.
but i m confuse that someone told me that i cannot use it as tilt sensor in moving condition.it can be used as tilt sensor only when it is not moving(stationary condition).
any ideas?

 

[vandelay]

An accelerometer can be used for tilt measurement while moving, but is not percise when you accelerate because the sensor cannot distinguish gravity from acceleration. In applications such as an RC airplane, where the acceleration is not immense, the accelerometer can still be used as a reference, but it will need correction from a gyroscope. The two sensors will need to be fused in a Kalman-type filter, an extremely complex statistical filter, but luckily for you, you can find simple implementations in C language online; Google for "tilt.c" by rotomotion, and you will find a simple filter that fuses 1 gyroscope (Analog Devices has nice gyros too) with 2 axes of acceleration measurements, and produces an optimal angle estimate. That code can help you do exactly what you want.

EDIT: Assuming body-fixed Y-axis straight forward, X-axis right/left, and Z-axis up/down, you need a Y-axis gyroscope, and a X,Z-axis accelerometer. Since you don't use the Y acceleration component, the actual acceleration of your airplane will not present much error, however, the centripetal acceleration experienced while turning the plane, and the up/downwards acceleration experienced while climbing/descending is the forces that will corrupt your accelerometer readings.