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Thread: All MX dynamixel got uncalirated at the same time

  1. All MX dynamixel got uncalirated at the same time

    Dear All

    When I was working on my robot and I sent a commands to initialize the position of the servos, I got a quite crazy moves and I noticed that all MX (28 and 64) became uncalibrated - well actually when I connected with the dynamixel wizard from Robotis and asked for the 0, the servos moved to a totally different position.
    I have few AX12 as well on the robot but they were working fine - no need to do anything for them.
    By uploading the firmware on each MX servos, looks like that everything go back to normal - although I was unable to update the firmware on two MX28s.
    But before restarting the robot I would like to know if somebody in the community experienced something similar? Because I am puzzled - first time I am facing this problem...
    Thank you for you feedback
    Best regards

  2. #2
    Join Date
    Jun 2011
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    Re: All MX dynamixel got uncalirated at the same time

    I feel like this is something that's been seen in the past, and maybe associated with voltage spikes, but never really tracked down. Too lazy to search the forums myself, though. JWatte/Tician/KurtEck were likely involved, iirc.

  3. #3
    Join Date
    Sep 2010
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    Re: All MX dynamixel got uncalirated at the same time

    The most likely culprit for a servo getting its ID reset to '1' is a brown-out. Sudden drop in voltage causes servo to reboot and briefly sits in bootloader mode waiting for firmware upgrade; the incoming dynamixel packets confuse the bootloader and it performs an ID reset. Purely speculation since I've never tried digging through the firmware on the ATmega88 or listened in on the DXL buss during an upgrade, but I'm thinking that the bootloader immediately sets the ID to 1 to correctly respond to the firmware upgrade program and an aborted upgrade causes it exit the bootloader without changing the ID back to its previous value.

    I've only known MX servos to lose their calibration data in a single situation. The servos involved had their gearsets replaced and firmware upgraded to a fairly recent version before performing the recalibration with the new gearset. After this, the darwin-op upgrade firmware program was run, which downgraded the servos to an older firmware. Not sure if it was caused by how/where the calibration data was stored between the two firmware revisions, or if the downgrade somehow reset the calibration data to the values used with the old gearset. It was a reproducible issue, and I have never known it to occur under any other set of conditions.
    Last edited by tician; 10-23-2015 at 02:12 AM.
    Please pardon the pedantry... and the profanity... and the convoluted speech pattern...
    "You have failed me, Brain!"
    gives free advice only on public threads

  4. Re: All MX dynamixel got uncalirated at the same time

    Gertlex, Tician Thank you very much for your answers.
    Actually to give more information, when I connected to the buss with the dynamixel wizard, I can see the servos, ID did not change (not set to 1) but when I asked servos to go to 0 position, all of them moved to another one (see pic below).

    Then If i want to assign a new position with the "goal position" gauge, they did not move.
    But after uploaded the firmware, everything went back to normal. Looks like the motors were not damaged because the robot behaves as before.
    Something happened that corrupted the firmware but not the motors...
    Voltage spike is possible, I will search in the forum for some hints...
    Can it be the OpenCM9?
    Thanks again

  5. Re: All MX dynamixel got uncalirated at the same time

    Click image for larger version. 

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    oups here is the pic mentioned in my previous post

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