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Thread: Dynamixel AX-12A won't actuate if the chain is longer than 6

  1. Re: Dynamixel AX-12A won't actuate if the chain is longer than 6

    Hi guys, thanks for your replies!

    My hardware is setup as follows:

    11.1V goes in:
    - 8 dynamixels
    - a voltage regulator that turns the 11.1V into 5V

    The 5V from the voltage regulator output goes in:
    - the 5V pin on the Teensy 3.6, which is OK because the Teensy 3.6 has an internal voltage regulator that turns it into 3.3V

    I am not bothering with return packets of the communication as I don't need to read any data from the servos, so the half-duplex is not an issue in my case.

    TTL level signal was not strong enough and would be corrupted. That is if the signal dropped to a low enough voltage, the voltage for a high value may not be high enough to register as a high... More about this in regards to Teensy.
    -> I use a 3.3V - 5V TXB0104 level shifter (bidirectional) between the TX from the Teensy 3.6 and the data pin of the servos so I don't think this is the problem

    The code did not properly know when a packet was completely sent out before it would switch back to RX mode and some of the packet could be trashed.
    -> Since I am using the Sync Write function that does not imply any return packet, it shouldn't be what you're saying right?

    In conclusion it looks like the problem is due to what tician was saying:
    Last I heard, the consensus as to the cause of resetting IDs is that a brown-out (undervoltage) event due to overtaxing the power supply and/or wiring issues causes the servo to reboot and temporarily enter its bootloader.

    @Brooks: If I understand correctly, you are using your own wiring harnesses to connect the Dynamixels together?

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    Re: Dynamixel AX-12A won't actuate if the chain is longer than 6

    Quote Originally Posted by zhanginou View Post
    @Brooks: If I understand correctly, you are using your own wiring harnesses to connect the Dynamixels together?
    For my Hexapod I'm using AX-18's. At 2 amp stall current per servo, that adds up to 36 amps. Obviously they're not stalled all the time, but to me this is FAR beyond the standard power wiring capabilities, especially around the standard power switch and initial power distribution.

    My current U-shaped harness is all 14 ga at the center of the hexapod, and reverts to standard wiring down each leg.

    I feel that it was equally important to get good data-signal conditioning. Using a separate driver IC and clamping diodes REALLY cleaned up the signal.

    I obtained good clean power, and a nice clean data signal, and all my problems went away.

  3. #13

    Re: Dynamixel AX-12A won't actuate if the chain is longer than 6

    FWIW, the Teensy has built-in support for half duplex driver chips; you can tell it to set a particular pin high or low based on whether the UART is transmitting or receiving.

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