Flight Core USB Power



  • When doing firmware development or basic Flight Core setup with QGroundControl such as loading custom firmware I prefer to not need the Power Module. Unfortunately the USB connector on the Flight Core does not pass through the +5V so the board can't be powered by USB alone.

    To fix this issue I hack into the provided USB cable and attach a second 4-pin connector to the +5V and Gnd wires that then can provide USB power to the CAN connector J8. See photos.

    IMG_20220513_112157452.jpg IMG_20220513_112115133.jpg

    This is not ideal, but it gets the job done. I've asked Modal AI to consider making this cable themselves to sell or provide with the Flight Core kit.

    I'm sure the concern is browning out the +5V from the USB.


  • Dev Team

    @Andrew-Keefe nice one!!!!! I actually hadn't thought of this simple approach! I see no issue here. The "no power via USB" is something that has bugged me for a while.......
    The original reason is that this design is shared with VOXL-Flight and we can't power VOXL-Flight off USB, but if/when next rev goes out the door, we'll make a modification to change this.

    For now, you mind if I steal these photos and put on our docs?


  • Dev Team

    Yes, this "can" work, but it is not ideal due to the many unknown variables on someone's host PC. Hence it is not a default option, and we would not recommend it. Issues can range from USB VBUS being out of spec (as it is, it is allowed +/- 10% which puts it in on the edge of our needs), and most "correctly designed" PCs will not provide more than 100mA unless a device is enumerated that asks for more. I'm not sure if all version of PX4 do that correctly. 100mA is insufficient for most use cases.
    In a strictly "QGC config" mode, I can see this work, but it is not something we plan on supporting on this version board due to those risks above. This also opens the door for someone to leave that power feed in-place while then later connecting the power module which will create a serious power rail shorting problem between the module and the PC.
    However, we do have a design already figured out that can take USB power for QGC/Config type of applications, and it validates the VBUS through a smart fuse/mux before using it. This will allows us to globally claim support, and if someone's system is not correct or out of range, we protect the HW.
    Stay tuned!


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