On-the-wire definitions for absolute gimbal commands

Discussion in 'MōVI Pro API' started by Steve Heppe, Jul 11, 2019.

  1. Steve Heppe

    Steve Heppe New Member

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    I'm currently using the Movi Pro with great success using rate commands (achieving very smooth and precise pointing), but I'm having trouble with the absolute angle commands. I am attempting to build the command messages directly using the on-the-wire definitions in Appendix A of the API. The rate commands work great, but when I attempt to send absolute angle commands, the Movi jerks uncontrollably. So it is clear that I have a misunderstanding on how to generate these messages. I am hoping that answers to a few questions will help me to understand better.

    First, please confirm my understanding that the Movi will report RZ, RY and RX values based on its IMU, not shaft positions, so there may be some drift between the two (this is okay -- just trying to understand).

    Second, if the gimbal reports that its Z axis (pan) is at 50 degrees (decimal value = 9102), and I want it to rotate clockwise to 55 degrees, do I send an absolute command (i.e., with GimbalCntl flag = 0b10) using GimbalRZ = +5 (as a signed 16 bit integer representing the value 910) or +55?

    If the gimbal reports RZ = -178, and I want to rotate counter-clockwise 4 degrees to +178, what command do I issue? I would like to avoid a "near-complete" rotation in the opposite direction.

    Can I expect smooth results if i issue absolute commands requesting large rotations (greater than 1 degree), or should I issue commands for very small shifts, and just keep issuing small offset commands until i get where I want the gimbal to go?

    I'm successfully issuing the rate commands using a signed 16-bit integer -- but is this correct for absolute commands? Should I break up the parameter into two separate 8-bit bytes with the MSB of the first byte indicating +/-, or is it proper to use the same signed 16-bit integer format as with the rate commands?

    Thanks in advance for your answers!
     
  2. Deniz Ozgoren

    Deniz Ozgoren Support Mage
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    What is your control rate? Make sure it is at least 50Hz. 20 is not enough for absolute.
     
  3. Steve Heppe

    Steve Heppe New Member

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    Yes, it is between 50 and 75 Hz (trying for 100 Hz, but my control loop is still a little slow).
    -Steve
     
  4. Deniz Ozgoren

    Deniz Ozgoren Support Mage
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    Also recommending you use Blackjack software if not already
     
  5. Steve Heppe

    Steve Heppe New Member

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    Hi Deniz,
    Please send me a link to the Blackjack software (Google searches only turn up the card game). Also, if you know any of the answers to the questions in my original post, I would certainly appreciate knowing them... it would help me a lot. Thanks!
     
  6. Graham Futerfas

    Graham Futerfas Well-Known Member

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    Here's the Beta (Blackjack) firmware Page: https://freeflysystems.com/support/movi-pro-support/beta

    To add the Beta app to your iPhone, you have to click on the iOS link on your phone (not your computer), and it will link to an app called Test Flight, which is in the App Store.
     
  7. Steve Heppe

    Steve Heppe New Member

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    Thanks Graham,
    I'll check our firmware versions later today. I'm currently driving the Movi Pro from my laptop, but our ultimate goal is to use a Raspberry Pi in an unmanned mode on a moving platform (although we will have remote real-time access to the Pi). Do you know the answers to any of my original questions? I think it would help a lot to get me "calibrated" and avoid false starts. Thanks!
     
  8. Graham Futerfas

    Graham Futerfas Well-Known Member

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    You'll need your phone to install the Beta firmware, but as Deniz said, it may be helpful for what you're doing. They may have worked out a few bugs. Deniz is probably one of the few people who can help you in this area, since he works on the programming side of things.

    To be honest, I have no idea what you're talking about -- it's way over my head! But it sounds cool. Good luck!
     
  9. Steve Heppe

    Steve Heppe New Member

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    Thanks Graham,
    I'll keep going, and hope that Deniz can offer some guidance. Have a nice day!
     

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