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Thread: Teensy 4.0 and Dynamixel

  1. #1
    Junior Member
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    Teensy 4.0 and Dynamixel

    I am trying to get a Teensy and Dynamixel AX motor working together without a chip to switch RX and TX but I cant seems to find a proper library that just works.

    Some libraries that state are for Teensy are not even compiling, is there something ready or I need to get around the source of DynamixelSDK and get some functions out?

    I see these examples https://github.com/ROBOTIS-GIT/OpenC.../ping/ping.ino but still trying to insall the proper way.

  2. #2
    Senior Member+ KurtE's Avatar
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    I am probably going to convert my stuff to new library by robotis. Dynamixel2Arduino, but default stuff depends on transmit enable pin... I have my own library https://github.com/KurtE/BioloidSerial which I earlier did some t4 testing on. Don’t remember if I added the 54 half duplex support or not

  3. #3
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    Quote Originally Posted by KurtE View Post
    I am probably going to convert my stuff to new library by robotis. Dynamixel2Arduino, but default stuff depends on transmit enable pin... I have my own library https://github.com/KurtE/BioloidSerial which I earlier did some t4 testing on. Donít remember if I added the 54 half duplex support or not
    Oh cool, I mean I dont mind using the chip to select the output, I just struggle to get a library that makes the telemetry works.

    At the moment I managed to use this https://github.com/jumejume1/AX-12A-servo-library and force to use Serial2 but it doesnt seems to decode the incoming messages, I can print out the bytes but it looks like there is an error coming out. I probably need to read the manual and see what it is suppose to send and receive.

    I will have a look at your library

  4. #4
    Senior Member+ KurtE's Avatar
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    @max246 - For a long time, I never used a buffer chip(s) to work with AX servos from a Teensy 3.x.

    However, most of the time I do now.

    Why, a couple of reasons, which arguably may not be totally valid, but since I had some doubts, I went to buffer(s)

    a) Dynamixel Spec shows that they are expecting 5v TTL. I never had issues I could pin on the fact that The T3.x and now T4 output 3.3v. I did run into issues where at times one or more AX servos would reset their ID to ID #1. Enough so, that some of the software I have for example to run a 3DOF hexapod, avoids Servo ID #1, and at sketch startup time, it searches for all of the servo IDs it expects. If it finds that one is missing and now servo ID #1 exists, it automatically changes the servo with ID #1 to the missing servo ID... If it finds that multiple servos are missing it does not do this... I personally think the resetting the servo to #1 is probably more an issue of power going into the servos and maybe they have a brown out...

    b) The IO pins on the T3.6 and now T4 (earlier T3) are NOT 5v tolerant. So again depending on HOW a servo (or other devices you might put on your Dynamixel chain), generates it's response (does it drive signal high and low, or only pull low), I was afraid that maybe something will generate 5V and damage the Teensy...

    Warning since I am mostly a tinkerer, I have played around doing this a few different ways. Often never fully testing the hardware, before I am off doing other things. But I plan to get back to trying my own T4 boards soon. However I am currently doing testing and making suggestions to Robotis to their library (and Arduino code) geared around their OpenCM9.04 boards. But I am doing this with the idea of better supporting the Teensy.

    Example board, which I still need to try to fully assemble one and test out the connections for servos... I was tinkering with idea of making a simpler one, that removed some of the complexities. Like maybe don't worry about SD connections, or in the case of this one I had a setup for a wireless module, which could be removed...

    Click image for larger version. 

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    Problem is I get too many distractions to finish my previous distraction.

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