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Thread: AX-12A Ping issue

  1. #11
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    Re: AX-12A Ping issue

    Quote Originally Posted by brennonwilliams View Post

    I am assuming that everyone else gets a perfect PING response and 0 fluctuation in the reading of the current position etc - every time on a normal solution?
    Not sure about ping but when I query my dynamixels, the current position always fluctuates within one tick (if I query repeatedly). Once I have it though I very rarely ask for it again. I've seen the same thing in the Dynamixel Wizard as well on AX-12's, AX-18's, MX-28's and MX-64's.... Always within a tick, just bounces back and forth.

  2. Re: AX-12A Ping issue

    Quote Originally Posted by KevinO View Post
    Not sure about ping but when I query my dynamixels, the current position always fluctuates within one tick (if I query repeatedly). Once I have it though I very rarely ask for it again. I've seen the same thing in the Dynamixel Wizard as well on AX-12's, AX-18's, MX-28's and MX-64's.... Always within a tick, just bounces back and forth.
    Yes, the position varying by one tick is just noise, that's normal.
    And right now I just quickly tried a loop pinging 4 AX-18A in a loop without delay, no error after thousands of ping... That 's the expected output.


    Quote Originally Posted by brennonwilliams View Post
    I tested my power supply which I think is either a problem - or the wall point is, and at the very least worth removing from the area of doubt. Voltage is steady at 12.1v but Amps are jumping from 4.8 - 6.7!
    That's a lot for current a few AX-12, unless they are driving some serious load...
    Moving 4 AX-18 with no load I rarely go over 1A. With all servos idle, I have a 0.15A consumption.
    ---
    Personal blog: http://xevel.org
    USB2AX documentation: http://xevelabs.com

  3. Re: AX-12A Ping issue

    I am cautiously optimistic that a solution is apparent.

    I removed the power and built up a new power unit with a desktop PSU to guarantee the consistency. I pulled out an old laptop with Win 8.0 on it and when I installed RoboPlus, I went through and selected the FTDI drivers directly from the LN101 folder, even though they are not the correct version. From that moment, all 3 devices would show up every time on the search inside the Dynamixel Wizard.

    I then uninstalled everything from the Win 8.1 machine and did exactly the same, using what appears to be the wrong driver from the LN101 folder, and Dynamixel Wizard now finds all 3 devices consistently.

    The FTDI drivers are indeed version 2.08.02 which is not even available from FTDI anymore - you will note on their site that version 2.12.0 is the only driver recommended for Win8.1 - having tried and failed to install that, plus having proven 2.10 doesn't work, it is my belief that these older drivers are the ones to use. I also note that FTDI had issues with communication dropping with V2.08.30, specifically with USB2Dynamixel previously.

    It should also be noted that this consistency is present regardless of the Latency setting on the port.

    A word also on power - I noticed that device 2 in the daisy chain always took more current - sitting constantly at 121 volts, while the other 2 were almost always on 118. I don't understand why this is, but the 121 appears to be related to the fluctuating values in position. When I dialled the desktop power unit back to the recommended voltage of 11.1, device 1 dropped to 114 and the other two sat at 118 - with no fluctuating position reporting.

    I have asked FTDI to provide the latest drivers in a file package - and if they do, I will test them and place them in the forum for others should it prove to work.

    For now, I want to say a big thank you for your help Xevel and KurtEck. It has been an interesting process, one which has forced me to look at every setting, read every document and get to know the Dynamixel AX-12A very well.

    I now have some further issues to sort out with regards to my code, but I shall start a new thread for that.

    Cheers

  4. #14

    Re: AX-12A Ping issue

    I noticed that device 2 in the daisy chain always took more current - sitting constantly at 121 volts, while the other 2 were almost always on 118.
    Those values are actually divided by 10 to get volts :-)

    And those are measured on the AX servos by a 10 bit ADC that has a bit of noise in the lowest bits, and the actual voltage is constructed through a voltage divider that doesn't use ppm-precision resistors.
    Combine a 1% nonlinearity in the ADC and a 1% error in the voltage divider, and you can easily get the difference between 11.4 and 11.8 Volts in readings.

    Also, those Volt readings are useful for figuring out how strong your battery charge is, and how much loss you may be getting through your hookup wire daisy chain. They don't tell you anything directly about how much current a particular servo is drawing from the voltage source.

  5. Re: AX-12A Ping issue

    My apologies, I was relaying the values shown from inside the Dynamixel Wizard (which come to think of it, could do with being converted).

    Thanks for the tip about using them as an adhoc battery level. Very good!

    Cheers

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