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Thread: MX-64AR not responding to instruction packets

  1. Exclamation MX-64AR not responding to instruction packets

    Hello all,

    I am having some problems with my MX-64AR. I am using a TTL to RS485 (MAX485) module to communicate to the servo. I go between using an Arduino and a Beaglebone Black to communicate with it. Today, I attempted to wire 4 servos together and control them all. Two out of four of them had their light indicator turn on and off to show that they were powered properly. When I attempted to send a message to a servo, nothing happened. I took an individual servo out, powered it by itself and attempted to control it and nothing happened. I took a servo that I had not power in the chain and that one still responses to my messages (light turns on, servo moves, can read back ID, etc). I used a 12V 1A source to power the chain, and I believe that may be the problem. I did not try to actuate them, but attempted to turn all of their LED indicator lights on and off.

    I have attempted to send a reset signal to the servo, but nothing seems to change. Any suggestions on what I should do now to get the servo to response?

    thank you,

  2. #2
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    Re: MX-64AR not responding to instruction packets

    What baudrate are you using with the servos that do not appear to be responding? In the likely event that the 12V1A supply was inadequate for testing, it is possible that one or more of the instruction packets combined with a brown-out condition triggered the servos to perform a full reset to factory settings (57600bps with ID=1).
    Please pardon the pedantry... and the profanity... and the convoluted speech pattern...
    "You have failed me, Brain!"
    bleh

  3. Re: MX-64AR not responding to instruction packets

    Quote Originally Posted by tician View Post
    What baudrate are you using with the servos that do not appear to be responding? In the likely event that the 12V1A supply was inadequate for testing, it is possible that one or more of the instruction packets combined with a brown-out condition triggered the servos to perform a full reset to factory settings (57600bps with ID=1).
    I am using 57600bps and ID=FE. And still nothing seems to get through. I have checked the information sent by the arduino with a logic analyzer and the information is proper. I have also checked the differential pair output with a oscilloscope and the information is being sent.

  4. #4

    Re: MX-64AR not responding to instruction packets

    No servo will send back data in response to FE, because that is broadcast. However, you can still use this to write registers, such as "turn on LED."
    Also, servos will not actually move, unless you first turn on the "torque enable" register, and then send a value for the "target position" register.

    Do you have a USB2Dynamixel (or replacement, such as USB2Ax)? If not, you should get one. Working with Dynamixel servos without being able to use the Dynamixel Wizard when things are unclear is a recipe for pain...

  5. Post Re: MX-64AR not responding to instruction packets

    Quote Originally Posted by jwatte View Post
    No servo will send back data in response to FE, because that is broadcast. However, you can still use this to write registers, such as "turn on LED."
    Also, servos will not actually move, unless you first turn on the "torque enable" register, and then send a value for the "target position" register.

    Do you have a USB2Dynamixel (or replacement, such as USB2Ax)? If not, you should get one. Working with Dynamixel servos without being able to use the Dynamixel Wizard when things are unclear is a recipe for pain...
    I do not have a USB2Dynamixel. I am beginning to understand why I should have purchased them a while back. I ordered this morning, but they are currently backordered so I am not sure when I can begin working with my servos again. Any ideas on how to factory reset the servo, or get the servo to work again using commands?

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    Re: MX-64AR not responding to instruction packets

    Are the LEDs turning on at all when power is applied? If it does not even flash at initial powering, there is likely damage to the circuit board.

    Apparently PING is supposed to work regardless of ID used (even the broadcast ID), so that might produce some response. Otherwise, you can emulate the RoboPlus Dynamixel Wizard method of finding servos by cycling through all valid baudrates and all valid IDs asking for a register's value (usually two bytes of the model number) (waiting for a response or a timeout before moving on to the next). It can take a while to finish if you do an exhaustive servo search. Faster is usually connecting the servo to the Dynamixel Wizard firmware restorer/upgrader using the USB2Dynamixel since it sends some sort of universally acknowledged command packet at some universal baudrate that the servos listen at during the first few moments after powering on.
    Please pardon the pedantry... and the profanity... and the convoluted speech pattern...
    "You have failed me, Brain!"
    bleh

  7. Re: MX-64AR not responding to instruction packets

    Quote Originally Posted by tician View Post
    Are the LEDs turning on at all when power is applied? If it does not even flash at initial powering, there is likely damage to the circuit board.

    Apparently PING is supposed to work regardless of ID used (even the broadcast ID), so that might produce some response. Otherwise, you can emulate the RoboPlus Dynamixel Wizard method of finding servos by cycling through all valid baudrates and all valid IDs asking for a register's value (usually two bytes of the model number) (waiting for a response or a timeout before moving on to the next). It can take a while to finish if you do an exhaustive servo search. Faster is usually connecting the servo to the Dynamixel Wizard firmware restorer/upgrader using the USB2Dynamixel since it sends some sort of universally acknowledged command packet at some universal baudrate that the servos listen at during the first few moments after powering on.
    Yes, the LED flashes on and off when power is applied. The proper boot sequence seems to be happening.

    I will try the method you mentioned and see if I can solve the problem that way.

    Thank you for your help. I will get back to this thread with my results, when I am finished testing this out.

  8. #8

    Re: MX-64AR not responding to instruction packets

    Any ideas on how to factory reset the servo, or get the servo to work again using commands?
    Well, the factory reset requires the USB2Dynamixel...

    Hooking up one servo, and using the PING command for each possible baud rate, is a good thing to try.
    You can also send a turn-LED-on register write using the FE broadcast address, to see if it's listening.
    When my bot is idle, I flash all LEDs in sync every second this way to show that the system is still alive.

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