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Thread: Reading Dynamixel's position in Wheel Mode

  1. Reading Dynamixel's position in Wheel Mode

    Hello,

    After some googling I still don't have a clear answer. It seems that higher end models (MX-28 and EX-106+) will return a valid position value (overflowing) in wheel mode. All other models have a dead zone and this caution note in their manuals: "If it is set to Wheel Mode, the value cannot be used to measure the moving distance and the rotation frequency".

    I'm most interested in AX-12A behavior. Can someone verify that they read valid position values in wheel mode (except when in dead zone) from AX-12A?

    Thank you,
    Paul
    Last edited by pauljurczak; 10-28-2011 at 06:35 AM.

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    Re: Reading Dynamixel's position in Wheel Mode

    See here.

    The MX-28 has a single magnetic encoder that produces an absolute position for the entire 360 degrees of rotation, in both wheel and servo modes, with values from 0 to 4095.
    The EX-106+ has a rotary encoder for wheel mode that does not produce an absolute position value, only a relative value (a 16-bit counter that increments for CCW rotation and decrements for CW rotation with each count being ~0.06 degrees). It also has an absolute position sensor (standard potentiometer?) that only produces a valid value when in servo mode (with the same dead zone as all other non-MX series servos).
    The AX-12A, like all other dynamixels not described above, cannot produce a valid position value when in wheel mode (it is even stated in a big yellow box preceded by a graphic exclamation point).
    Last edited by tician; 10-28-2011 at 09:01 AM.
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  3. Re: Reading Dynamixel's position in Wheel Mode

    Thank you for clearing this up. BTW, the thread you linked to contains this from Robotis guy: "... the new MX-28 (and other MX series) ...". Do you have any information about other MX series?

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    Re: Reading Dynamixel's position in Wheel Mode

    No idea about anything yet, but it is not unexpected that they would shift more of their existing products to the newer controller/sensor boards. No more worn potentiometers (contactless magnetic encoder), higher dynamixel bus data rates (72MHz STM32 vs 16MHz of the ATmega8), and 32-bit math for position and speed control (32-bit ARM Cortex-M3 core versus 8-bit AVR core of the ATmega8).
    Please pardon the pedantry... and the profanity... and the convoluted speech pattern...
    "You have failed me, Brain!"
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