Comments

• 

  Chris Gough November 29, 2012 at 12:36am

  @Shayam, if you want to experiment with quaternions, DCM, euler angles, etc. you might want to check out the various pluggable AHRS subsystems in paparazzi.

  http://paparazzi.enac.fr/wiki/Subsystem/ahrs
• 

  Shyam Balasubramanian November 29, 2012 at 12:24am

  @Randy, Thanks for that nice explanation on accelerometer with quads! Now, my understanding gets better.

  I would want to try out Quaternions once myself, it seems different people are having different opinion. My friend, who works purely on Quad uses quaternion. He mentioned to be that it was 'much' faster than DCM. But, since truth is one but scenarios differ, I will ask him if he can lend me some benchmarking ;)
• Developer

  Randy November 29, 2012 at 12:15am

  @Shyam re Quaternions,

       There's a thread by Bill Premerlani re DCM vs Quaternions.  My understanding is that they're equivalent.  II think perhaps DCM is faster but maybe not, i'm not sure.  I don't think it's as simple as one has 4 elements so it's faster than the other that has 9.

       When the copter/plane accelerates in any direction, the accelerometers sees this.  The problem is that we generally use the accelerometers to tell us which way is down.  So any acceleration of the copter/plane has the potential to throw off our attitude estimate.  Normally the accelerations are short-lived so they don't cause much problem but if they're long lived (for example you're constantly travelling in a circle) it can be a real problem.

  -Randy
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  Shyam Balasubramanian November 28, 2012 at 2:51pm

  @Randy,

  Thank you for your thoughts on implementing quaternions. I have a question, quaternions are supposed to be faster as they use 4 elements unlike DCM which uses 9, and does not suffer gimbal locks (even DCM does not, but one should know how to avoid it there though), it must result in faster computation right?

  And what does "the centrifugal (centripetal) force which can throw off the accelerometers" means?

  Thanks!
• Developer

  Randy November 26, 2012 at 12:41am

  @Shyam re "using quaternions in APM"
       We pulled out the Quaternion attitude estimation from ArduCopter after 2.6.  It didn't perform better than DCM so it was just slowing down the developers who had to maintain two parallel ahrs classes.  You can find 2.6 in the downloads area but can't make any promises about being able to support it or what incompatibilities with the mission planner may have appeared.

      If you want to try it you should add this to your APM_Config.h:

  #define QUATERNION_ENABLE ENABLED

   

  Now if you're talking about using the attitude estimation from the MPU6000's DMP unit (which spits out it's results in Quaternions), you can simply add this to your APM_Config.h:

  # define DMP_ENABLED ENABLED

  A few people on the dev team have flown it (including me) and from the limited testing we did, it's results were nearly identical to the DCM but it doesn't offer us some features that DCM does like centrifugal (centripetal?) force which can throw off the accelerometers.

   
• 

  Shyam Balasubramanian November 25, 2012 at 7:03pm

  "Quaternion implementation in APM - 1. Can somebody PLEASE give me a hint on how to use it? I am stuck."
• Zachary Koh October 31, 2012 at 8:17pm

  @Brint Thanks for the suggestion! It looks pretty neat.
  I am flying a custom frame so my team will have to design our own mount. How's the response of the servos for you? Are you using the ones available on the website as well?
  I take it your servos are all connected to the outputs of two channels on your APM right? I was also wondering if I could use a seprate transmitter, from the one I use to fly, to control the camera rig.
• 

  Brint E. Kriebel October 31, 2012 at 8:21am

  Zachary, probably best to start a new topic for this in the forum. I just picked up one of these, though, and I am quite happy with it: http://quadframe.com/products/g01k
• Zachary Koh October 31, 2012 at 12:32am

  Hey guys,

  I was thinking of throwing an actively stabilizing camera rig onto my VTOL copter. Anyone has experience with camera-servo rigs? Any advice would be greatly appreciated. X)
• 

  Dean Miller October 27, 2012 at 7:12am

  Shhhh, it is the dark side of the code we are never to speak of.

   

  Actually I didn't even know I posted, must be a bug in my Windows 7, fortunately Windows 8 is coming and will fix all bugs. :)