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Servo Inconsistencies between New and Legacy Controllers

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  • Servo Inconsistencies between New and Legacy Controllers


    We have noticed that the new Modern Robotics (MR) servo controllers don't seem to allow as much freedom of movement with the HiTec servos (we are using the 485-HB and 755-HB models) as the legacy technology.

    When we use the MR Core Legacy Module connected to the old Tetrix servo controllers and set the full range of motion from 0.0 to 1.0, the servos act as expected giving us a full 180 degree freedom of motion.

    However, using the same code with the same phones, we connected the servos to the new MR servo controller through the Core Power Distribution Module (CPDM) and the servos stop short about 30 degrees of the full range on both ends. The code prevents going beyond the 0 to 1 limits, so we can't get the full range of motion that way.

    Has anyone else experienced this problem? And does anyone have a workaround to get the full range of motion on the servos with the new control modules?

    Thanx in advance.

  • #2
    Other threads on these forums (I'm too rushed to find them right now) point out that the 180 degree servos only swing 145 degrees with the new MR Core Servo Controller, but 180 degrees via the MR Core Legacy Module.
    A search for 145 might be profitable.
    The cause appears to be (for reasons I / we don't understand) that MR's new design cannot move the pulse widths as far within the PWM signal as the old controllers could. This is based on measurements by some forum members using oscilloscopes.
    I am hoping (this is only a hope) that MR will figure out how to fix this for the next season via a firmware update (or even a recall / refurbish plan).
    For myself, I thought I was going crazy or we had a bad servo... I no longer think this (at least not in this regard).
    Good Luck!
    Martin Haeberli
    Mentor, FTC 7593, TigerBots


    • #3

      Thanx for the info. Apparently, I am very late to the party.

      For those who might find my post rather then the original one discussing this issue, it is here: