Tim McMahan

75 dollar IMU

I haven't gotten my first Ardupiilot up and running yet.  I'm hoping to do some GPS navigate at ground level, then put it on a plane.  I'm still trying to decide what is best for me to stabilise the plane.  The simplest seems to be the FMA co-pilot system, but its also one of the more expensive, and seems somewhat limited.   An IMU seems to be the way to go, though I still; don't FULLY undrerstand them.  Do all IMU's output data the same way?  Are the Gyros and accelerometers operating similar to an RC heli rate gyro and heading and hold gyro?  
   A friend of mine linked me to a site where he's looking into FPV equipment, and Ii was looking around when I stumbled onto this 6 dof IMU for 75 bucks.  Does it work any differently than other IMU's?  If so how?
http://www.flytron.com/50-imunext-6-degrees-of-freedom-imu.html


Thanks in advance,
Tim

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Peter SeddonPermalink Reply by Peter Seddon on February 8, 2010 at 9:17am
This really only forms the basis for an IMU - ie it is the gyros and accelerometers. You will need some type of processor and software to be able to call it an IMU.

Peter
Tim McMahanPermalink Reply by Tim McMahan on February 8, 2010 at 9:46am
Soooooooo, the ArduIMU also runs a small processor on board to translate the accelerometer and gyro data into something more friendly for the Ardupilot?
Chris AndersonPermalink Reply by Chris Anderson on February 8, 2010 at 10:10am
Yes, and the software it runs (called a DCM) is the real rocket science. IMUs are a dime a dozen; what you want is an AHRS, which is an IMU plus the computational power to make it useful. That's what ArduIMU+ is.
Tim McMahanPermalink Reply by Tim McMahan on February 8, 2010 at 10:42am
AHHHHHHHH. Thanks Chris. I'll get this figured out yet, lol. I suppose that's half the fun though isn't it? AHRS = Attitude Heading Reference system, right?

http://en.wikipedia.org/wiki/Attitude_and_Heading_Reference_Systems

Also, through previous discussions here, i found out why I have to use both acceleromters AND gyros, kind of a checks and balances system. What input does the ardupilot really HAVE to have though? What if.....I were to input the ArduIMU + board (ArduIMU without sensors, right?) with only accelerometers (which I have), and then put my rate gyros(which I have) in line between the servos and Ardupilot? Does the Ardupilot do something with ALL that information from the gyros, or just knock the bumps out of the controls? I can put them in line between my Rx and servos doing straight RC flight as is, and get a stable enough flight to look unnatural. Of course, its only taking out the twitches/bumps. If I let go of the plane in a dive, it'll dive very smoothly into the ground.

Just trying to learn more. :)
Tim
Tim McMahanPermalink Reply by Tim McMahan on February 10, 2010 at 2:03pm
Ok, so I'm rethinking how to do this again. And I'm trying to apply the K.I.S.S. technique. If I skip the shield at first, can I install an FMA XY sensor directly to the Ardupilot, and use fly by wire mode? I'm on a tight budget, and it works out better for me to buy just one or two things at a time. From reading the manual it would SEEM that I could use just ONE FMA sensor with v2.1, and do fly by wire. THEN I could add the shield, add another sensor and go to v2.5, THEN add GPS and do anything.

Is that reasonable?
Tim

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