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  • External UVC Camera and Powered Hub

    Hi Folks,

    There is an "Advanced Topic" on the Wiki that provides some information about using an external UVC camera with a powered USB hub this season.

    https://github.com/ftctechnh/ftc_app...owered-USB-Hub

    Tom

  • #2
    Hi Tom,

    We are using an External UVC camera with a powered USB hub ("P-HUB") and MR modules (we bought extra MR modules in a previous season and we don't like to send stuff to the landfill unnecessarily).

    We would like to connect the MR CDIM to the P-HUB upstream of the MR CPDM ("PDM") so as to:
    • put the CDIM (sensor data) on a faster USB bus
    • reduce the number of USB hubs in between the CDIM and the RC phone
    • eliminate the CDIMs contention with other MR modules over the PDM's limited USB bandwidth
    • elevate CDIM communication priority over other MR modules
    • raise the CDIM communication priority to the same level as the external UVC camera(s)
    Also, allowing CDIM(s) to be connected to the P-HUB potentially reduces the total number of USB hubs on the robot. There are only 7 USB ports on the PDM and teams often need 8 MR modules. I think you will agree that when you have 8 MR modules in total, it is against sound engineering and system design principles to have to add a USB hub downstream of the PDM when you can simply plug the CDIM into one of the free ports of the P-HUB.

    Ultimately the P-HUB is always going to be in the path between the CDIM and the RC phone so I think that there is no reason that the CDIM cannot be connected directly to the P-HUB and many reasons why it should not be connected to a PDM downstream of the P-HUB.

    Also, if I were using REV Expansion hubs instead of MR modules, I would love to be able to plug a CDIM into the P-HUB upstream of the REV Expansion hubs. However the rules say the CDIM must be plugged into the PDM, which essentially prevents the use of a CDIM for teams using REV expansion hubs.

    Last but not least, reducing the number of USB hubs on the bot increases reliability and decreases complexity and thus makes FTAs jobs easier. Therefore, with all these benefits and no foreseeable drawbacks, I presume the reason why the GDC has ruled against allowing the CDIM to be connected directly to the P-HUB is because the Tech team hasn't tested and approved it. If this is the case, I request that the Tech Team test and approve the CDIM(s) to be connected to the P-HUB upstream of the PDM so that the GDC can allow this.

    Comment


    • #3
      Alec: that makes perfect sense to me. I can't see any engineering or safety reason that this should be disallowed.

      Comment

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