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Thread: Open CM9.04 - How to connect to AX (or MX) servos?

  1. #1

    Open CM9.04 - How to connect to AX (or MX) servos?

    Suppose I would like to try out their current version:

    And I don't want to buy a bunch of their XL servos but maybe instead try it maybe on PhantomX hexapod...

    What have people done to use AX servos with these. I could probably just use 3 jumpers to connect to an AX/MX hub.

    Could probably buy an XL servo to get a cable to cut to splice to AX servo cable...

    Could buy 3 of the cables to use one to splice:

    Other options? Like is it setup that I could easily un-solder a connector on the CM9.04 and solder in an AX compatible one (I have many of these sitting around).


  2. #2

    Re: Open CM9.04 - How to connect to AX (or MX) servos?

    FYI I found my board and it was a type B so it had two ax connectors on it
    next up see how I want to power it

  3. #3

    Re: Open CM9.04 - How to connect to AX (or MX) servos?

    I use a hub, and a cable that I cut off one connector, and stripped the ground and power wires. Alligator clips complete this highly robust solution :-)

  4. #4

    Re: Open CM9.04 - How to connect to AX (or MX) servos?

    Like your solution

    I was also pointed to this solution:

    I am also guessing that from their manual:
    That the differences between A, B, C, that I could probably take a C and un solder one or more of the small connectors and then solder in the standard AX type connectors.

    Besides I need to try out my new powered solder sucker, that I picked up after someone mentioned it up on the PJRC forum:

    Playing around a little bit with the B version should probably receive a new C version next week or so. So far with the B I can download simple programs using the Robotis_openCM IDE, but the Arduino IDE with the Robotis Arduino stuff compiles but the board hangs when it tries to download to it. Will investigate more, maybe some updated firmware needed.

    I am also unsure if I properly updated the COM port to their driver. I think it is, but...

  5. #5

    Re: Open CM9.04 - How to connect to AX (or MX) servos?

    I typically get version A, and I have a bunch of the right AX/MX-style connectors in the parts bin.
    I think I got 100 of them from Digi-Key at some point. I'm almost out by now!
    I also have male break-off pin headers in the bin, so getting the savings of model A and customizing it with only the bits I need is slightly more economical.

  6. #6

    Re: Open CM9.04 - How to connect to AX (or MX) servos?


    I have a lot of those connectors sitting in my cabinet as well.

    I now have two of the Version A (Plus their connector set, a Version B and Version C.

    The Version C came with OpenCM 485 expansion board I mentioned.

    I have a version of my AX Servo test program somewhat limping along. Still some issues I am resolving.

    It is sort of interesting that the servo connectors on the 904 board are connected to Serial1 of the process. Where as the connectors (5 TTL and 5 485) on the 485 board are controlled on Serial3. So question is do you stick with one dynamixel porthandler objects which you configure to pass in "1" or "3", or potentially have two of them to handle both. Then using code would have to know which object to use to send to specific servos.

    Also trying to figure out a matching connector for the 4 pin Serial2 connector: 20010ws-04
    Did not yet find the part on digikey or mouser. But probably can figure out it is probably 2mm spacing.

    Edit: I have some 2mm to 2.54 mm jumpers ordered which can work, plus I can also probably use the outside (non populated) connectors on the CM9.04 (A4/A5 I believe). Will try these out with XBee
    Last edited by KurtEck; 12-16-2017 at 06:01 PM.

  7. #7

    Re: Open CM9.04 - How to connect to AX (or MX) servos?

    Quick update and questions...

    I did solder an 904a with the AX servo connectors, I also used double long breakout pins, such that I could plug it into the 485 board and be able to connect to the pins from above. As you can see in:
    Click image for larger version. 

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    I then tried powering up the 485 board and put a servo on the 904a board and tried to talk it... Figured out that there is servo power brought from the 485 board to the 904 daughter board. Can probably create a simple jumper for this...

    In case anyone is interested in size of the 485 board, here is a picture of it, along with some others...
    Click image for larger version. 

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    The 904 boards are about the same length as a Teensy 3.6 or 3.5, but .2" wider. Or about the same width as the breakout board shown below it. The picture shows a straight 904, Teensy and ...

    What I am wondering is how are others using these cm904 boards with their robots?

    Are you simply making an adapter cable from small servo to normal servo cable and going to a powered AX/MX hub? If so wish there was a standard cable for this.

    Are you using an XBee? If so how are you wiring it. Wish there was a standard adapter like the zigbee one.

    I wish there was an easy way to check the voltage coming in to the board. Don't see in voltage divider, but maybe I am missing something?

    Any sound? I personally like some form of Audio feedback. Could use external buzzer. Wonder if any of the pins on the 904 are a DAC pin? Will look later.

    All for now.

  8. #8
    Join Date
    Sep 2010
    Rep Power

    Re: Open CM9.04 - How to connect to AX (or MX) servos?

    The 4-pin cable for Robotis ZIG/BT modules should be a JST PH header, just like the two little 2-pin battery connectors. I'm not sure anybody is using the CM-904 for anything except light mechs using XL servos. jwatte often recommends the CM-904 for beginners to dynamixel servos, but not sure they actually use them in any of their bots anymore. Now that there is true Arduino support for the CM-904, it might become a bit easier to use and more popular, but the Teensy still wins out in just about every way.
    Please pardon the pedantry... and the profanity... and the convoluted speech pattern...
    "You have failed me, Brain!"

  9. #9

    Re: Open CM9.04 - How to connect to AX (or MX) servos?

    Thanks Tician,

    Right now playing with some double jumpers, where one side are 2mm and the other side the 2.54mm, I now have the XBee talking to the commander.

    As you probably can tell, I also like the different Teensy boards as well!

    However it would be nice if maybe Trossen would would be able to migrate away from the AVR Arbotix board to some commercially available board ARM board that has support for dynamixel servos and is supported. So I thought it would be a worthwhile experiment to see how well the CM-904 would fit the job.

    Also it will be fun to have a version of the code base that no longer is setup with all of the AVR support things and can do things like use some form of IntervalTimer to do the interpolation and the like. So far I have some the code limping along. I now have it receiving data from the Commander. It sure is nice not having to share the XBee serial port with the USB code, so you can have easily do debug output (and input)...

  10. #10

    Re: Open CM9.04 - How to connect to AX (or MX) servos?

    For the heck of it, I was playing around with diptrace today to see how hard it would e to create some form of minimal board for a CM904 to plug into in order to make it have a few of the things I might want. Not saying I would actually build one, but might as it would not cost too much and not hard to solder...

    A simple WIP. Here is a 3d output from Diptrace of a quick and dirty layout.
    Click image for larger version. 

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    If I go any farther with it, will change a few things like maybe move the RX/TX/RSSI LEDS to above the XBee as to keep any routing going to that area... PLus add in mounting holes.

    What this has:

    A connector to plug in CM904... Note wrong 3d image right now. Showing generic 2x20 DIP. Don't have a 3d model for CM904 yet. I also have a row of pins that run along both sides of the socket to allow one to add another row of breakout pins.

    A connector to be able to plug in a wall wart or Lipo battery... The output of these feed into the DXL Power+ and - pins of expansion header

    4 AX/MX TTL connectors. This is connected to the DXL Data pin and the DXL Power +- pins
    I added Caps for DXL, +5v, 3.3V pins.

    Added XBee connector, which is powered by the 3.3v of 904 and is connected to Serial2 (A4 and A5 pins). It has leds on the TX/RX and RSSI connections

    Added 3 additional LEDS on D18-20...

    Added simple buzzer circuit. Currently setup for D22, not sure if better choice.

    Voltage divider hookup for DXL voltage going to A0 pin.

    Again just playing around. Not sure if any of this is worth doing or not.

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