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Thread: How to power AX-12A servos connected to an USB2AX?

  1. How to power AX-12A servos connected to an USB2AX?

    Following the problem I describe on my previous thread "AX-12A servos with OpenCM 9.04: can actuate but not read", I bought an USB2AX to try to solve it, but... RobotCenter is unable to detect my servo through the USB2AX! So I suppose that's because it cannot power the servo, that you need another external power supply. Is this true? must the servo be powered to detect it and reflash its firmware? If so.... how? Here they just say "you can use a powered controller (CM-5, CM-510, CM-730, CM-900, Arbotix…)". I have an OpenCM and an expansion board, but I have no idea how to connect it to the USB2AX and servo to power the servo but use the USB2AX to control it.

    Thank you a lot!

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    Re: How to power AX-12A servos connected to an USB2AX?

    The servos need 10-12v to move properly. The data input line runs at TTL levels (0 - 5v). I would use a 12v power supply to run the servos. Ensure your USB2AX and your 12v supply share a common ground.

  3. #3

    Re: How to power AX-12A servos connected to an USB2AX?

    must the servo be powered to detect it and reflash its firmware? If so.... how?
    Yes!

    The cheapest is to cut one of the connector cables, and strip the wires for power, and connect power/ground. (Make sure you connect them the right way! Else you may ruin the servo) This assumes you have a suitable battery or power supply with 10-12V output, and crocodile clips, and that you know how to keep them from banging into each other and short out :-)

    The safest way is to buy the Trossen AX/MX power hub: http://www.trossenrobotics.com/6-port-ax-mx-power-hub
    Robotis has one, too, but I like the Trossen one better (for example, there are some traces on the Robotis hub that are surprisingly flimsy, and may become hot spots when driving multiple servos!)

  4. Re: How to power AX-12A servos connected to an USB2AX?

    mmm... somehow I knew that I was asking something really easy... and that the obvious answer would make me feel shame

    Thanks a lot. I can now detect my servos on RoboPlus!

    But... all this history bring me back to my original problem: "AX-12A servos with OpenCM 9.04: can actuate but not read",

    And this didn't get solved after successfully executing the Dynamixel Firmware Recovery; all looks fine on RoboPlus, can command and configure the servo, and read all: pose, temperature, speed...

    Click image for larger version. 

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    But when I try back with the OpenCM code, for example with PyPose or a simple getPosition, again I always get 0xFFFF.
    Rather frustrating.... any parameter I should try to tweak on the servo? maybe baudrate, or increase the timeout (as this is the error code I always get; is Return Delay Time such a timeout?)

    Thanks again!

  5. Re: How to power AX-12A servos connected to an USB2AX?

    Well... I give up. I assume that the new OpenCM B with only one TTL 3-pin port somehow fails to read from the servos with the existing OpenCM 1.0.2 code nor with DynamixelQ.

    So... as I have now a USB2AX, the solution is obvious: migrate to the Dynamixel SDK. At least I expect to get better performance than by controlling the arm through the OpenCM!

  6. #6

    Re: How to power AX-12A servos connected to an USB2AX?

    I assume that the new OpenCM B with only one TTL 3-pin port somehow fails to read from the servos with the existing OpenCM 1.0.2 code nor with DynamixelQ.
    No, that shouldn't be it.

    Anyway, if you have a USB2AX, that'll work, too.

  7. #7

    Re: How to power AX-12A servos connected to an USB2AX?

    Yep, USB2AX and a SMPS2Dynamixel (plus a 12V supply) works great!

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