rounin
Posts: 12
Joined: Mon Feb 20, 2012 8:05 am

Re: 9 axis IMU

Sun Apr 08, 2012 6:19 am

I've got another sensor board drawn up & sent for prototyping that I am planning to use in a robot built around a RasPi.

It is a 9 axis IMU with a Maetro Wireless 2100A GPS, Invensense MPU6000 Acceleromoter + Gyro, and a STM32 f103 microcontroller. IO and power are provided over a mini usb port.

I am planning for this board to run a kalman filter, and some other filtering / correction on the gyro data, which is why it has a relatively fast microcontroller. I'm hoping that the f103 is fast enough to offload all the filtering math from the RasPi, saving some time on the main processor.

Current lead time for the hardware is 2-3 weeks, hopefully it works!


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gordon@drogon.net
Posts: 2020
Joined: Tue Feb 07, 2012 2:14 pm
Location: Devon, UK
Contact: Website

Re: 9 axis IMU

Sun Apr 08, 2012 6:26 pm

rounin said:


I've got another sensor board drawn up & sent for prototyping that I am planning to use in a robot built around a RasPi.

It is a 9 axis IMU with a Maetro Wireless 2100A GPS, Invensense MPU6000 Acceleromoter + Gyro, and a STM32 f103 microcontroller. IO and power are provided over a mini usb port.

I am planning for this board to run a kalman filter, and some other filtering / correction on the gyro data, which is why it has a relatively fast microcontroller. I'm hoping that the f103 is fast enough to offload all the filtering math from the RasPi, saving some time on the main processor.


Looks intersting... Have you seen the ArduPilot project? They're handling a 9DOF IMU plus GPS and sonar with an 8-bit microcontroller (and controlling the props with it too).

I have some APM (ArduPilotMega) kit and wrote a load of custom software for it for a while last year but the project never got ff the ground as it were (the people I was working for stopped funding it). Plenty of oomph in an 8-bit CPU for flight control, so anything better is just going to be a bonus. (especially if it doesn't need the millisecond response of something flying)

You might want to look at Quaternions  rather than (or as well as) Kalman too..

Gordon
--
Gordons projects: https://projects.drogon.net/

rounin
Posts: 12
Joined: Mon Feb 20, 2012 8:05 am

Re: 9 axis IMU

Sun Apr 08, 2012 8:18 pm

Yup, I have seen the ardupilot. A friend of mine used one on his UAV with good results, I almost went with that rather than building my own, but part of this is just for me to learn, and I did want to tweak a few things in their design anyway. I'm thinking about using some of their code, haven't looked yet to see how much I can share. I'm making my own to save a little cost by removing the barometer, and have a faster onboard mcu, and have direct USB connection. When the 9 axis (accel+gyro+magnetometer) invensense chip comes out I am going to use that as well. I'm looking to do full inertial navigation w/ lots of filtering (it seems the MPU6000 has pretty terrible zero rate drift and temperature effects), so I figured it would be better just to over design a little than have an underpowered chip (and its still only 5$! things have advanced so much : ) ). I'm planning on running the accelerometers as fast as they can go, would like the sensor to be the limiting factor (might switch to more accurate gyros later, if I can find relatively cheap fiber ring gyros... was looking at KVH's website and they all say "ask for price", not a good sign).

The Kalman filter and quaternions do different things. Quaternions represent a rotation about a line, similar to a euler angle / rotation matrix (and good point, they are better because there is no singularity, but they take more processor time as the matrix is larger), and the Kalman filter is a way to combine data from different sensors, sensor error models, and vehicle dynamics model to perform data fusion and more robust inertial nav solutions with accuracy information (the all important standard deviation in addition to the "you are here").

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SN
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Location: Romiley, UK
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Re: 9 axis IMU

Sun Apr 08, 2012 10:15 pm

Quaternions. . . (shudder) hard work
Steve N – binatone mk4->intellivision->zx81->spectrum->cbm64->cpc6128->520stfm->pc->raspi ?

hzrnbgy
Posts: 106
Joined: Mon Dec 26, 2011 10:55 pm

Re: 9 axis IMU

Mon Apr 09, 2012 5:30 am

Spoken like a true geek

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