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Thread: XL-320 communication issues.

  1. XL-320 communication issues.

    Hey all, I've been having some issues with trying to control some XL-320's via a Raspberry Pi 3 through a usb2ax module.

    I've tried a lot of stuff at this point but still am at a dead end. The usb2ax module runs fine, and I can can connect and control my servos via Robo+ on my PC just fine with the same electronics setup, the only difference being moving a usb extension cable with the usb2ax at the end from the Pi to my PC.

    I did some messing around with using an OpenCM 9.04 board to read the info from the data pin of usb2ax and sent it into Tera Term so I could log it. [Data]. The serial output from the Pi looked... really inconstant. I've tried to eliminate as much noise from external sources as possible, which was an issue I was having trying to get this working earlier. The images on that google slides page shows the electronics in each configuration.

    I'm not sure what kind of other information to share that could be of assistance in helping to figure out what is going on, but if anyone has an ideas i'd love to hear them and am open for trying almost anything at this point.

  2. #2

    Re: XL-320 communication issues.

    Do you have an oscilloscope or logic analyzer?
    A few things I would check based on the symptoms you see:
    - the name of the device is different on Raspberry Pi, and you're talking to the wrong serial port
    - the Raspberry Pi console hasn't been disabled and interferes
    - the baud rate is somehow set differently on the Raspberry Pi and you're talking at the wrong baud rate

  3. Re: XL-320 communication issues.

    Quote Originally Posted by jwatte View Post
    - the Raspberry Pi console hasn't been disabled and interferes
    I do not think this is probable, the serial that can be messed up by other processes of the distro is the hardware port, not a ttyACM like the USB2AX.
    ---
    Personal blog: http://xevel.org
    USB2AX documentation: http://xevelabs.com

  4. #4

    Re: XL-320 communication issues.

    Unless the code somehow relies on defaults.
    Without seeing the code that sets up the TTY, we're all shooting in the dark anyway.

  5. Re: XL-320 communication issues.

    I don't have an oscilloscope or logic analyzer.
    Checking with lsusb pulled up all the correct data on for the usb2ax, that and with some of this testing, it was the only device connected via usb to the Pi itself, and it correctly reports the baudrate at 1 Mbps. Looking at the hex outputs from the serial and comparing them does show that they are quite similar, which i'd expect them to be very different if the baud rate was incorrect or something was locking the port all together.

  6. #6

    Re: XL-320 communication issues.

    Okay, so you've verified the serial data.
    How are the XL servos powered? The 9.04 provides power, but the Pi does not.

    Also, what software is writing to the port?

  7. Re: XL-320 communication issues.

    The servos are powered through a 6 Port AX Hub, the one with the included barrel jack and screw terminals, and a nimh battery pack that puts out about 7.6v at full charge. I've confirmed the battery setup works with the servos because the same electronics setup was able to be connected to and controlled via Robo+ on my PC only by moving the usb2ax module.
    I'm not sure if my issues are caused via a grounding issue, and if it is i'm not really sure how to remedy it as i've never had a similar problem if that is the cause.

    I was / is / might be using pyusb2ax to try and connect, and I've tried out a few other wrappers for the modified dynamixel_sdk that supports the usb2ax and none have really worked. I'm not to familiar with working with linux and I've recently lost a lot of free time I was planning on working on this with so i've yet to figure out how to compile stuff straight from c so I can run stuff more directly.

    Sorry for the delayed response, but it has to do with the aforementioned reduction in free time.

  8. #8
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    Re: XL-320 communication issues.

    Which dynamixel protocol are you using? AX, RX, and MX servos all use dxl1.x, but XL-320 and Dynamixel Pro servos all use the dxl2.0 protocol and will not respond to dxl1.x.
    Last edited by tician; 09-03-2016 at 09:48 PM.
    Please pardon the pedantry... and the profanity... and the convoluted speech pattern...
    "You have failed me, Brain!"
    [git][mech][hack]
    gives free advice only on public threads

  9. Re: XL-320 communication issues.

    No idea how the wrapper I was using works, what I would need to check what protocol version it is using from the sdk, or how I would potentially gain that compatibility either by writing my own wrapper or just using the default sdk. Nor do I know much about the dynamixek_sdk itself. This is my first real venture into dealing with hardware control, most of the stuff i'm use to dealing with is simulated.

    If i've learned anything from trying to work on this is that it is far out of my normal scope of knowledge, so sorry if I'm making stupid mistakes or asking silly questions.

  10. #10
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    Re: XL-320 communication issues.

    PyUSB2AX is apparently just a wrapper for the dxl1.x SDK for use with AX, RX, and MX servos, so will not work with dxl2.0 servos like the XL-320. I'm thinking that Robotis released a dxl2.0 SDK and it is very likely others have made their own, but not sure what exists for python.
    Please pardon the pedantry... and the profanity... and the convoluted speech pattern...
    "You have failed me, Brain!"
    [git][mech][hack]
    gives free advice only on public threads

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