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Determining Current Draw of Servos

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  • Determining Current Draw of Servos

    Because servos have no ability to give feedback on position, it would be useful to measure the current draw of the servos... A spike in current draw would indicate the servo is being resisted, so could indicate that a gripper has grabbed an object, or is hitting a barrier for example.

    Is anyone aware of an off-the-shelf sensor for this? Or is there any documented (I couldn't find it) or undocumented method supported by the Rev Expansion Hub for measuring/sensing servo current draw?

  • #2
    The Expansion Hub does in fact have a current sensor on the servo bus, and RevExtension2 provides support for it, however due to (an assumed firmware bug) the reading it returns is totally erratic and useless. However, what you might be able to do is use RevExtensions2 to sum up the current draw for all 4 motors and the DIO bus, and then subtract that from the total module current draw to obtain theoretically the servo bus current draw.

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    • #3
      If the servos in question are running off a SPM however, then that approach would not work. The only way to measure current draw through the SPM would be to put a meter on the 12v line going to it, which is not allowed by the GM

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      • #4
        I am unable to find much (via google) on RevExtension2... Is there an API document somewhere, or a wiki? Thanks much for the info.

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        • #5
          Originally posted by HumanJHawkins View Post
          I am unable to find much (via google) on RevExtension2... Is there an API document somewhere, or a wiki? Thanks much for the info.
          The readme on the GitHub repo should provide enough information for you to get started: https://github.com/OpenFTC/RevExtens...ster/README.md

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