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Thread: Power layout for Dynamixel chain

  1. Power layout for Dynamixel chain

    Hi, I've got 6 AX-12A servos and the 12V, 10A power supply, all bought from Trossen. Also using a USB servo controller. however I forgot to buy the AX-MX Power Hub. My question is about doing this wiring manually. How would the layout be?

    Unfortunately this isn't quite enough for me



    best regards,

    Daniel S

  2. Re: Power layout for Dynamixel chain

    A followup:

    Found this related info here:

    - Simple Power cable (must be used at the end of the bus):
    Cut a Dynamixel cable and solder a battery connector or battery cable to the GND(-) and VDD(+) lines. Protect the solder joints with heat-shrink tubing or electrical tape. You can the DATA line altogether.


    - Y power cable (can be used in place of any other cable):
    Cut the GND and VDD lines of a Dynamixel cable around the middle, be careful not to damage the DATA line. Solder both halves of each cable to your battery connector or cable, GND on - (black), and VDD, the middle one, on + (red). Protect the solder joints with heat-shrink tubing or electrical tape.
    That's almost clear but I'm not sure what "at the end of the bus" or "in place of any other cable means". It seems everyone just takes this for granted.
    Last edited by ZanQdo; 06-03-2015 at 07:31 PM.

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    Re: Power layout for Dynamixel chain

    Every dynamixel servo has two connectors/sockets for cables that are connected to each other through wires inside the servo housing. This means that one servo can be connected only to a second servo through a 3-pin cable, and yet the first can still be powered and communicate with a USB2Dynamixel attached only to the second servo.

    In theory, every single servo connected to the bus though any other servo or hub can be powered from a supply attached anywhere, but resistance in the wires means that the most feasible design is usually a central hub to provide power to multiple strands of servos (to prevent large drops in voltage to servos farthest from power source when current through wires increases). The USB2Dynamixel/USB2AX can be located just about anywhere on the bus, but when not using a hub to increase the number of free sockets then the only free socket to add the USB2Dynamixel to the bus is at either end of a strand of servos.
    Please pardon the pedantry... and the profanity... and the convoluted speech pattern...
    "You have failed me, Brain!"
    bleh

  4. Re: Power layout for Dynamixel chain

    Thank you Tician that explains things. I got this diagram from xevelabs.com that might help others bumping into this thread. The only thing I don't quite understand is why is it OK to connect the battery's VCC to the USB2AX VCC output, isn't that dangerous to the host computer or something?

    Click image for larger version. 

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    Re: Power layout for Dynamixel chain

    Pretty sure the USB2AX is like the USB2Dynamixel, where the VCC pin of the connector socket is not actually electrically connected to anything on the PCB. As long as you don't bump anything conductive against the exposed pins to short VCC to anything else, there is no danger from it.
    Please pardon the pedantry... and the profanity... and the convoluted speech pattern...
    "You have failed me, Brain!"
    bleh

  6. Re: Power layout for Dynamixel chain

    Right! That makes sense, thanks man.

  7. #7

    Re: Power layout for Dynamixel chain

    My question is about doing this wiring manually
    The good news is: If you have wire strippers and a soldering iron, you're in good form!
    (A 100-1000 uF capacitor to parallel with the power would be an additional bonus.)

    Cut one of the existing Dynamixel cables in two. Strip the "GND" and "+12V" wires and solder them to a capacitor and wires that go to your power supply. Done!
    This cable can now plug in at the end of a strand, or into a Dynamixel hub of your choice.

    Just don't tie GND to TTL, and TTL to GND...

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