Me and a friend want to work on a four rotor helicopter over the summer, these things needs to constantly measure it's angle in mid air and adjust pwm duty for each motor constantly so it does not flip over in midair.
I know of two kinds of sensors to use, gyros and accelerometers, accelerometers can measure gravity and thus can act as a gyro
Barometers needs to be very very very very sensitive to do this, infrared and sonar rangers can't go too high or outdoors, not practical at all
The problem is, say the wind accelerates the helicopter at 0.5 G to the left, the helicopter will think that it is tilted 45 degrees to the right, and thus it will speed up the right side motor and slow down the left side motor in an attempt to rebalance itself. This means it will accelerate EVEN MORE to the left. So the slightest movement in mid air might cause the helicopter to go crazy and crash
I can get sample accelerometers for free from ST Microelectronics and Freescale, and they don't cost too much to buy (under $10, and SOIC). Gyros on the other hand, costs $30 each and Analog Devices are not gonna give me any for free, also not solderable by hand (ball grid)
The question is, is there a way for a MCU to decide whether the helicopter is moving or tilted? How does the wii remotes do it so well?
mechanical swivel devices holding the accelerometers will not work