Any one working on a 9 Axis IMU?

I am getting started on developing an IMU for the paparazzi system. Anyone that would like to throw in their comments and ideas would be appreciated. In the end I can read the tech docs and come up with a lot of the values myself but I might need an electronics genius to help me out eventually.

I am looking at developing around a few sensors here.

Gyro: http://www.sparkfun.com/commerce/product_info.php?products_id=9801

Triple-Axis Digital-Output Gyro ITG-3200

Mag: http://www.sparkfun.com/commerce/product_info.php?products_id=244

MicroMag 3-Axis Magnetometer

Accel: http://www.analog.com/en/sensors/inertial-sensors/adxl325/products/product.html

Analog Devices ADXL325

The guys and gals over at vector Nav hae done a great job with their Sensors
http://www.vectornav.com/vn-100-features

However, I am interested in learning for myself and prototyping rather than having someone do the work for me. Yes I might just buy their sensor to get myself up and running but I am more interested in the learning process of the hardware itself and the programming.

Eventually, all of this will be placed into a higher speed UAV that I am trying to design at the moment. Jet engine based system with thrust vectoring and quick control surfaces. I know that I am merely skimming the surface of the art of IMUs but I am wondering what I can accomplish with my own two hands and what we can accomplish as a community.

Sure we have done 9 axis IMUs and AHRS systems using them. Quite a few in this community; UAV Dev Board, ArduIMU with external magnetometer, ArduPilotMega with external magnetometer, Sparkfun 9DOF Razor, etc.

The place to start your investigation is understanding the different types of filters which can produce a useful AHRS system from an IMU for use in an airframe that is not moving slowly. This is where many (most perhaps) fail. For example VectorNav (at least the last time I looked) fails to account for centripetal acceleration, making their IMU fairly worthless in an aircraft moving with any velocity to speak of. The DIYDrones "mainstream" is to use a fixed gain filter based on an approach developed by Bill Premerlani using the direction cosine matrix. Others in the community use Kalman filters, which require a little more processing horsepower than you get with Arduino processors, but which can synthesize more data sources into a solution.

I have not played with anything as radical as a turbine airframe, but I did get a foam pusher to fly at rooftop level at about 100km/hr very close in around a building to win a competition. My IMU had no problem with high roll rates, high centripetal forces, and tightly banked turns. The gyros you are considering are much better than the gyros in that IMU. We are considering the ITG-3200 for several upcoming projects here as well.

Good luck!

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Developer

Doug Weibel September 14, 2010 at 7:32pm

Sure we have done 9 axis IMUs and AHRS systems using them. Quite a few in this community; UAV Dev Board, ArduIMU with external magnetometer, ArduPilotMega with external magnetometer, Sparkfun 9DOF Razor, etc.

The place to start your investigation is understanding the different types of filters which can produce a useful AHRS system from an IMU for use in an airframe that is not moving slowly. This is where many (most perhaps) fail. For example VectorNav (at least the last time I looked) fails to account for centripetal acceleration, making their IMU fairly worthless in an aircraft moving with any velocity to speak of. The DIYDrones "mainstream" is to use a fixed gain filter based on an approach developed by Bill Premerlani using the direction cosine matrix. Others in the community use Kalman filters, which require a little more processing horsepower than you get with Arduino processors, but which can synthesize more data sources into a solution.

I have not played with anything as radical as a turbine airframe, but I did get a foam pusher to fly at rooftop level at about 100km/hr very close in around a building to win a competition. My IMU had no problem with high roll rates, high centripetal forces, and tightly banked turns. The gyros you are considering are much better than the gyros in that IMU. We are considering the ITG-3200 for several upcoming projects here as well.

Good luck!

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