The Vectornav VN-100 IMU (they call it an Attitude Heading Reference System, for some reason) is out and it looks like the best device on the market in this price range. Here's the description from the site.
The VN-100 combines a 3-axis accelerometer, 3-axis gyro, 3-axis magnetometer, and a high performance processor onto a single surface mountable chip-sized module to create a high performance orientation sensor. Fully calibrated for bias, gain, and misalignment, the VN-100 accurately calculates orientation over the entire 360° range at 200 Hz. Filtered orientation data and inertial measurements are assessible via either a SPI or RS-232 serial interface.
With its small size, high performance, and low cost, the VN-100 has numerous potential applications. A development kit is available for the VN-100 which comes with a sensor pre-installed and gives easy access to all of the sensor's features.
Features and Benefits:
Complete Sensor Package
3-axis accelerometer
3-axis gyro
3-axis magnetometer
Multiple Output Types
Heading , Pitch, Roll
Quaternion / DCM
Acceleration, Angular Rates, Magnetic
High Precision
Heading accuracy < 1.0 (static)
Pitch/Roll accuracy < 0.5 (static)
< 3 deg dynamic
Fast Onboard Processor
Extended Kalman Filter
200 Hz update rate
Surface Mount Package
Hand solderable
30 pads
Ultra-Compact Size
22 x 24 x 3 mm
3 grams
Fully Calibrated
Scale Factor and Gain
Axis misalignment < 0.05 deg
Hard / Soft Iron Compensation
Digital Interface
Serial UART up to 921600 bps
SPI Interface up to 18 MHz
Low Cost
$400 - 500
*Price depends on quantity
Dragos,
I agree completly. In using my PicPilot on several platforms I've come to the conlusion it would be better to have the magnetometer remotlely mounted. There just is no single place for mounting that is suitable for all platforms. My next revision will have it on a pigtail.
Faisal,
I bought some shielding material and have been experimenting with it. The problem is the shielding saturates in moderate magnetic fields. It helps but would require substantial (read heavy) shielding to eliminate the problem. Distance from the field does wonders which is why being able to remotly mount the sensor will help, at least on some platform. It's hard to get more distance on a Tri-Rotor or Quad-Rotor.
Has anyone tried using magnetic shielding on motor and other high current wiring?
This company makes magnetic shielding in a variety of forms: http://www.lessemf.com/mag-shld.html
Their "MµCord" is made for wiring, and it is $1.75 per foot. Would be interesting to see if this helps magnetometer readings.
Magnetic Shielding Materials
Learn how to Make Your Own Magnetic Field Shields With These Unique Materials
My humble opinion about the magnetic interference is that a really helpful IMU should provide the capability of remotely install the magnetic sensor. Even most of the real avionics solutions are like this.
Why? Because inertial sensors should be as close as possible to the gravity center (where, in case of an electric helicopter the motor sits) while the magnetic sensor should stay as far from any metal assembly or high current wires as possible.
I'd like to see VN-100 providing an alternate port for an external magnetic sensor - it would become then really helpful for an electric UAV.
My project's biggest challenge (a VTOL) is the fixed point flying and I really need a fast reacting IMU and don't care too much about GPS but I've already purchased the UAV DevBoard.
Currently my best option would be replacing the GPS with the magnetometer for the UAV DevBoard but implementing the 7 state EKF on the DSPIC... If someone implemented this in DSPIC pls. let everyone know (and eventually provide the code too :) )
Second option - get the VN-100 with a remote magnetometer.
I'd also like a copy or link to that 7 state EKF + the document that describes it. I am working on a quadrotor and I'm considering using the Mahoney et al algorithms (perhaps using quaternions, as they supposedly use fewer computations than DCM). I'd still like to understand the KF and related algorithms.
I basically just went through the Quick Start Guide and started recording video. I would like to put one on a Scorsby Table for a while in the near future and see how it does. My hands are a little too shaky to get very good data ;)
jack, i am sure if you find a correct placement in the plane, your (mechanical) compass will have very very small error. I can see a lot of quadrotors with compass.
This tri rotor puts an exceptional amount of current through the wires & is way beyond what a commercial AHRS has to endure, but it shows how much a magnetometer can be affected by a hobby vehicle.
Comments
I agree completly. In using my PicPilot on several platforms I've come to the conlusion it would be better to have the magnetometer remotlely mounted. There just is no single place for mounting that is suitable for all platforms. My next revision will have it on a pigtail.
Faisal,
I bought some shielding material and have been experimenting with it. The problem is the shielding saturates in moderate magnetic fields. It helps but would require substantial (read heavy) shielding to eliminate the problem. Distance from the field does wonders which is why being able to remotly mount the sensor will help, at least on some platform. It's hard to get more distance on a Tri-Rotor or Quad-Rotor.
Brian
This company makes magnetic shielding in a variety of forms:
http://www.lessemf.com/mag-shld.html
Their "MµCord" is made for wiring, and it is $1.75 per foot. Would be interesting to see if this helps magnetometer readings.
My humble opinion about the magnetic interference is that a really helpful IMU should provide the capability of remotely install the magnetic sensor. Even most of the real avionics solutions are like this.
Why? Because inertial sensors should be as close as possible to the gravity center (where, in case of an electric helicopter the motor sits) while the magnetic sensor should stay as far from any metal assembly or high current wires as possible.
I'd like to see VN-100 providing an alternate port for an external magnetic sensor - it would become then really helpful for an electric UAV.
My project's biggest challenge (a VTOL) is the fixed point flying and I really need a fast reacting IMU and don't care too much about GPS but I've already purchased the UAV DevBoard.
Currently my best option would be replacing the GPS with the magnetometer for the UAV DevBoard but implementing the 7 state EKF on the DSPIC... If someone implemented this in DSPIC pls. let everyone know (and eventually provide the code too :) )
Second option - get the VN-100 with a remote magnetometer.
I'd also like a copy or link to that 7 state EKF + the document that describes it. I am working on a quadrotor and I'm considering using the Mahoney et al algorithms (perhaps using quaternions, as they supposedly use fewer computations than DCM). I'd still like to understand the KF and related algorithms.
Thanks
Roy
https://www.youtube.com/watch?v=w-qEIkz90b4&fmt=18
I basically just went through the Quick Start Guide and started recording video. I would like to put one on a Scorsby Table for a while in the near future and see how it does. My hands are a little too shaky to get very good data ;)
I am grateful with you and your work!
This tri rotor puts an exceptional amount of current through the wires & is way beyond what a commercial AHRS has to endure, but it shows how much a magnetometer can be affected by a hobby vehicle.
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