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REV Expansion Hub Disconnect Issues

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  • REV Expansion Hub Disconnect Issues

    This problem has plagued us since we started FIRST 2 years ago. It always seems to happen at the worst times.

    We believe it to be an issue with our robot controller to hub connection or battery to hub connection.

    We use the rev xt30 power distribution block because we use the REV servo power booster module and 2 hubs. There are a lot of xt30 connections on our robot because of this.

    We use the REV Usb Retention Mount on our hub, but we do not have any retention mechanism on the OTG cable which connects the Retention Mount Cable to our robot controller phone.

    This seems like the issue, but the disconnects are so inconsistent in when they happen. They could happen when we bump or get bumped, or they happen if we run our intake and latch at the same time (lots of moving parts). Sometimes they dont happen for hours.

    The phone mount on our robot is this: https://www.thingiverse.com/thing:2547407

    tl;dr We need help troubleshooting "Rev Expansion hub disconnected", which we think stems from having no wire retention on our phone mount.

    Edit Other things I forgot to mention:

    We use moto G4 plays

    We use a REV magnetic limit switch sensor

  • #2
    Welcome to FTC! It is a rare team that doesn't have this issue. It is mainly a result of trying to use cheap quality electronics coupled with a poor system architecture.

    If you haven't already discovered it, you cannot ever have anything touching both USB cable connectors or power connectors, there cannot be any bumping or straining of these or you will have issues. Connect only wires to frame, and put strain loops that put a slight amount of tension to keep connectors in place.

    You could also have EMI issues, the grounding strap is recommended for the REV hub, but too bad if you don't already have one as REV is out of stock, and you cannot use anything else, which is incredibly stupid since a simple loop of wire with resistor will work just fine. (REV is out of stock of a lot of key components, like the Expansion Hubs! So sorry if you blow a hub, season over!)

    Edit: REV apparently has the resistive straps back in stock. Note they also have a little USB connector retainer to hold the USB cable firmly in the hub.
    Last edited by 11343_Mentor; 02-01-2019, 03:44 PM.

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    • #3
      Our team has also had problems with connecting. It has usually been fine in the past few months, but today it suddenly will not connect with our robot.

      We just connected it to a different REV Hub to test another system, and then connected it to our real robot, but it didn't read either Rev Hubs (we have two on our real robot, and one on our test chassis).

      We have been trying to figure out why it has occured, and we recently updated our Moto G phones to the Android version 7.1.1. Our phones Driver Stations are at 4.3. Are we missing any updates for the FTC App, or has their been any bugs or issues recently found?

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      • #4
        At our last comp, a lot of teams were having disconnect issues presumably from EMI/ESD charges.
        It cost us a match when ours died 2 secs before latching.
        One of the FTAs got us a ferrite choke to add to the USB cable between the phone and hub. No problems since then.
        I think the idea is that if you do get an ESD event, the choke at least stop it from traveling back to the phone and interrupting the communication. Sicne many teams have switched to OTG cables, they are not using the original USB-min to USB micro vables that have the choke built in.

        It really stinks we are not allowed to use more conventional ESD mitigation strategies... we have on e of the XT30 grounding straps and it doesn't do much....

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