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Thread: Arbotix Pro or Ordex with usb2ax to control dynamixel MX and possibly upcoming new version of dynamixel

  1. Arbotix Pro or Ordex with usb2ax to control dynamixel MX and possibly upcoming new version of dynamixel

    Hello, given that the Arbotix Pro and a new version of Odroid are available, I would like to get your opinion on which controller to use to control 20-30 dynamixel MX motors. The workflow is as following: 1. Create a motion data file (a time series of angle data) using a self-made simulator. 2. Import those angle data to the controller to drive the motors. 3. While the robot is moving, record the real angle data and possibly other parameters such as torque of all motors for later analysis. 4. Meanwhile, use sensory feedback such as FSRs under the feet and gyro to help the robot to maintain balance. In this case, should I get the Arbotix Pro or Odroid-XU4 with usb2ax? Any other recommendation appreciated. Thanks.

  2. #2

    Re: Arbotix Pro or Ordex with usb2ax to control dynamixel MX and possibly upcoming new version of dynamixel

    Hopefully someone else can give a more complete answer, but I will give my two cents...

    Currently the Arbotix Pro is setup as a Servo controller (like the USB2AX or the CM730), and is setup to be controlled by another main processor, like the ODroid. Example the HROS1 robot uses one of these to control the servos and it is connected to either an Intel Edison or an RPI, or some others of us have connected it up to the ODroid Xu4 (or C1)...

    Note: while I say it is like the USB2AX, it does have additional capabilities, like the ability to turn the power on and off to the servos, plus a built in IMU and the ability to read in several analog pins. Again the board is very much based on the Robotis CM-730 controller. More details about this in the manual: http://support.robotis.com/en/produc...8cm-730%29.htm

    As the Arbotix Pro may be able to do your whole task, I am not sure if anyone has tried to have it run with their own custom program. To do so, you would to use an external programmer and adapter. Also the instructions for building the current firmware implies that you need to build it under Linux. I have not tried it yet, but plan to at some point, as I wish to experiment adding functionality to the firmware. As of about a week or so ago, I now have a 2nd Arbotix Pro to experiment with. But before I do so, I may do most of my experimentation using a Teeny 3.2 on one of my adapter boards....

    Now if you go down the Odroid (Xu4?) with an USB2AX, you can have your program on the Odroid send the commands to the USB2AX to control the servo and likewise query the servos for some of the data you mentioned. You will then have to decide how you will connect up the other sensors. Example Gyro or IMU, probably USB. At least that is how several of us have them on or Hexapods to use with ROS... As for FSR's, will need something that can input Analog data. The Odroid C1 has two analog inputs. I don't believe the Xu4 has any analog inputs. Again several options. Could use something like an Arduino or a Teensy. Example currently playing with an Arduino Pro mini that fits into the feet of the HROS1 and reads in the analog values for four FSRs (Thanks to R3n33). Have code on the Arduino to emulate a servo, such that you don't have to run IO lines down to the feet... Again lots of options available.

    Hope that helps
    Kurt

  3. #3

    Re: Arbotix Pro or Ordex with usb2ax to control dynamixel MX and possibly upcoming new version of dynamixel

    The easiest option to do that is probably the OpenCM-9.04, assuming you run the power through a separate power injector/hub.
    The OpenCM-9.04 comes with Dynamixel libraries from Robotis, and can talk both version 1 and version 2 of the protocol, and has an adapter board for the RS-485 version of the bus ("R" servos.)

    Now, it doesn't have a lot of persistent storage. You have to either wire in a MicroSD card through the SPI bus, or you can use a second board (odroid, raspberry pi, or similar) over USB, or you can use wireless telemetry of some sort and capture the data on a PC. I ended up doing the latter -- ESP8266 based WiFi communication both for control, and telemetry, talking to that through a serial port on the OpenCM-9.04.

  4. Re: Arbotix Pro or Ordex with usb2ax to control dynamixel MX and possibly upcoming new version of dynamixel

    I recall that one of the limitations of the OpenCM-9.04 is that there is no support for sdcard and one has to do all the development. Is it still the same for sdcard and telemetry?

  5. #5

    Re: Arbotix Pro or Ordex with usb2ax to control dynamixel MX and possibly upcoming new version of dynamixel

    Yes, OpenDM 9.04 does not directly support an SDCard. It does have an SPI port, and you could wire up an SDCard holder, if you're good with those kinds of things.

    If you instead choose to send telemetry over USB serial, or over wireless serial, then you don't need to worry about the SDCard adapter.

  6. Re: Arbotix Pro or Ordex with usb2ax to control dynamixel MX and possibly upcoming new version of dynamixel

    Quote Originally Posted by jwatte View Post
    Yes, OpenDM 9.04 does not directly support an SDCard. It does have an SPI port, and you could wire up an SDCard holder, if you're good with those kinds of things.

    If you instead choose to send telemetry over USB serial, or over wireless serial, then you don't need to worry about the SDCard adapter.
    If I don't know how to send telemetry over USB serial or over wireless serial, what other option do I have?

  7. #7

    Re: Arbotix Pro or Ordex with usb2ax to control dynamixel MX and possibly upcoming new version of dynamixel

    If I don't know how to send telemetry over USB serial or over wireless serial, what other option do I have?
    Then I guess it depends on what you DO know!

    Do you need telemetry as logging for later retrieval, or over the air in real time?

  8. Re: Arbotix Pro or Ordex with usb2ax to control dynamixel MX and possibly upcoming new version of dynamixel

    Quote Originally Posted by jwatte View Post
    Then I guess it depends on what you DO know!

    Do you need telemetry as logging for later retrieval, or over the air in real time?
    I need some way to store the motor information (such as a time series of real rotational angle of all motors) for later analysis. If possible, I hope to be able to do real time feedback control.

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