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Update on USB Disconnect Issues (unable to detect USB modules during scan)

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  • Originally posted by Alec View Post
    This 7 port COTS USB hub, which isn't even highly rated, has eliminated the core module scan issues I was having with my PDM.

    I have 7 modules connected my COTS hub, including the CDIM and CLM. When the RobotController phone is connected dirctly to my COTS hub (no PDM in the loop), the RobotController can find all seven modules every time.

    Perhaps the capacitor fix is masking the root problem, the PDM. If FTC eliminates the root problem, then there will be no need to void the warranties of the core modules by adding capacitors.

    Tom, did MR graciously provide the serial numbers of the defective PDMs?

    Never mind graciously. Most of us will be happy with just plain old professionalism.
    Hi Folks,

    There are a lot of concerned and frustrated posts in this thread. I would like to try and address some of the concerns here because I think there is some misunderstanding/misinterpreting going on and there are some confusion over the issues surrounding the USB connection problems.

    First, I'd like to talk about the Power Distribution Module (PDM). Modern Robotics and FIRST have received a report of a small number of PDMs having issues on Power Up. What we have seen (and I saw first hand a team that had this problem) is that when you turn on your PDM the USB side of the device does not work. This means that if you connect your Android phone on the input side and a Core module (motor, servo, legacy, or device interface) downstream, the Android phone won't be able to see it because the USB hub inside the PDM is not working.

    From what Modern Robotics (MR) has seen this problem is fairly dramatic in the sense that if you have a defective or bad PDM, it will for the most part not work reliably. MR has developed a simple test to determine if your PDM is exhibiting this problem. The PDM has four blue LEDs onboard. If you look carefully at the PDM (see figure referenced below) there is an LED in the upper left hand corner (above and to the left of the words "CORE" and "P6"). This LED is labeled "USB Enabled" in the diagram...

    https://drive.google.com/open?id=0B0...3M5V3dnXzJMOVU

    If you are concerned that the USB hub of your PDM is not working properly, you can do a simple test. If you connect your PDM to a fresh 12V battery and turn it on, and then you turn on your competition approved Android phone and connect the phone to the input port of the PDM (see figure below) then the "USB Enabled" LED should turn on. This LED indicates that the USB hub within the PDM is working properly and that your Android is connected (as a master device) to the hub.

    https://drive.google.com/open?id=0B0...mNjTmlIWWYzTDg

    If you suspect that your USB hub is bad, you should try this test. If you suspect that your PDM is not working reliably (and there have been cases reported to MR of a few unreliable units) please contact Modern Robotics on the phone and they will troubleshoot the unit and work with you to resolve the situation. MR so far has seen only a small number (on the order of 1%) of the units shipped from their factory by late August 2015 are affected by the problem. MR rolled in a production change in late August 2015 so units shipped from the factory (to FIRST's fulfillment center) after August 24, 2015 should not experience this problem. If you think you have this issue (and the USB enabled LED won't illuminate for your hub) then contact them to get the unit repaired/replaced.

    There have been suggestions that teams be allowed to use commercial off-the-shelf (COTS) USB hubs. We currently do not recommend this. Note that the PDM uses a COTS USB chip (Texas Instruments TUSB2077A USB Hub) like many other COTS hubs do. However, unlike a typical COTS hub, the PDM can be powered by a 12V robot battery (it has a built in voltage regulator) and it was designed to tolerate the power spikes and fluctuations that can occur on the robot, tolerate Electrostatic Discharge (ESD) events on the robot, as well as the mechanical vibrations and jolts that occur on a robot.

    Note that in the Pilot Testing phase of this project, I personally did configure a pair of robots for test purposes to run with COTS (Belkin) USB hub using a switching 5V regulator to power the hubs from the 12V battery. The robots ran OK with this configuration, but it was not without its problems. One of the biggest problems that I saw is that for COTS hub the 5V pin for the input USB port is live (i.e., it is connected to the hub from the phone). This creates an interesting problem. I observed that when I turned off the main power supply on the robot (which provided power to the COTS hub) the devices connected from the hub would start to pull power from the Android phone instead of the 12V battery. With the power switch turned off, the COTS hub acted like a non-powered USB hub. This caused two problems... 1) the devices on the hub would draw current from the phone and could deplete the phone's battery pretty quickly. 2) when the power switched from the 12V battery to the phone, it seemed to cause a brownout condition on some of the USB modules and it left them in a weird, unresponsive state.

    The PDM was designed with certain precautions in mind and the 5V pin on the input port is disconnected so the modules will not pull power from the phone when the robot is turned off. In my experience this is a desirable feature.

    Another problem that MR has been seeing with a small number of PDMs is the blown out 5V regulators. They are working to debug this situation and trying to determine from the units they've received what the potential cause for the problem might be. If you have a non functioning or blownout PDM please contact MR immediately. However, at least for some of the PDMs that have had this problem, MR has confirmed with the users that the polarity on the input power was reversed. In certain confirmed cases teams have accidentally reversed the input polarity (connected the negative terminal of the battery to the positive input terminal of the PDM, etc.) and blew the 5V regulator onboard. MR is doing some testing to see if there are other issues that might be also causing the blown 5V regulators.

    The PDM comes from the factory with the Tamiya style connector. This is done as a safety feature. The Tamiya connector has a keyed design so that if you have a battery that came with the factory with a Tamiya connector and the PDM that came with the factory with a Tamiya style connector the user wouldn't physically be able to reverse the polarity because the keyed connectors would not physically connect.

    In order to mitigate the chances of a blown 5V regulator on your PDM, MR recommends using the original factory Tamiya connector on the PDM and the 12V batteries.. Also, MR does not recommend that users "backfeed" power to the PDM through the Anderson Power Pole connectors on the PDM. The input power to the PDM should be fed only through the input power cable.

    In summary, I think there has been some confusion regarding the issues surrounding the PDM. There appear to be some defective PDMs where the USB hub does not work properly. Checking the USB Enabled LED can help determine if you have a bad unit. This does not appear to be an issue with power management. it appears that there are some bad units that do not power on properly. It seems that units that have this problem will display this behavior even if they are powered by a fresh 12V battery.

    Again this PDM issue appears to be separate from the failure to scan on power cycling issue (which I'll try to address on another post...).

    Tom
    Last edited by Tom Eng; 10-31-2015, 07:07 AM.

    Comment


    • Thanks for the update, Tom.

      Originally posted by Tom Eng View Post
      The PDM comes from the factory with the Tamiya style connector. This is done as a safety feature. The Tamiya connector has a keyed design so that if you have a battery that came with the factory with a Tamiya connector and the PDM that came with the factory with a Tamiya style connector the user wouldn't physically be able to reverse the polarity because the keyed connectors would not physically connect.

      In order to mitigate the chances of a blown 5V regulator on your PDM, MR recommends using the original factory Tamiya connector on the PDM and the 12V batteries..
      That's fine, but FIRST has and continues to recommend swapping out Tamiya connectors because they fail after a small number of uses, as has been found for years by FTC teams. See for example, page 12 of the robot wiring guide, posted in this article, just updated by FIRST. It is similar to the recommendations that have been made for the past few years. It would be great if all sides of FIRST got together on this matter and agreed on recommendations.

      BTW, using permanently fused powerpoles on the batteries and PDMs prevents reversed polarity plugins. This would seem to be the best of both worlds. Is there a reason that FIRST and MRI don't recommend this solution?

      Originally posted by Tom Eng View Post
      Again this PDM issue appears to be separate from the failure to scan on power cycling issue (which I'll try to address on another post...).
      Many of us are eager to hear your thoughts on the scan on power cycling issue and Mitch's findings and proposed fix. Please post as soon as you can.

      Thanks again.
      Last edited by JoAnn; 11-20-2015, 12:04 PM. Reason: updated links

      Comment


      • Originally posted by Tom Eng View Post
        There have been suggestions that teams be allowed to use commercial off-the-shelf (COTS) USB hubs. We currently do not recommend this. Note that the PDM uses a COTS USB chip (Texas Instruments TUSB2077A USB Hub) like many other COTS hubs do. However, unlike a typical COTS hub, the PDM can be powered by a 12V robot battery (it has a built in voltage regulator) and it was designed to tolerate the power spikes and fluctuations that can occur on the robot, tolerate Electrostatic Discharge (ESD) events on the robot, as well as the mechanical vibrations and jolts that occur on a robot.

        Note that in the Pilot Testing phase of this project, I personally did configure a pair of robots for test purposes to run with COTS (Belkin) USB hub using a switching 5V regulator to power the hubs from the 12V battery. The robots ran OK with this configuration, but it was not without its problems. One of the biggest problems that I saw is that for COTS hub the 5V pin for the input USB port is live (i.e., it is connected to the hub from the phone). This creates an interesting problem. I observed that when I turned off the main power supply on the robot (which provided power to the COTS hub) the devices connected from the hub would start to pull power from the Android phone instead of the 12V battery. With the power switch turned off, the COTS hub acted like a non-powered USB hub. This caused two problems... 1) the devices on the hub would draw current from the phone and could deplete the phone's battery pretty quickly. 2) when the power switched from the 12V battery to the phone, it seemed to cause a brownout condition on some of the USB modules and it left them in a weird, unresponsive state.

        The PDM was designed with certain precautions in mind and the 5V pin on the input port is disconnected so the modules will not pull power from the phone when the robot is turned off. In my experience this is a desirable feature.
        Hi Tom,

        You say "We currently do not recommend this." I respectfully suggest that it is not just an option that is "not recommended" but instead it is an option that is prohibited by the game manual.

        You bring up various potential problems with using COTS hubs. I won't discuss the possibility that these problems could be addressed with the COTS hubs (e.g., find a way to disconnect the 5V pin, train teams to disconnect before powering off their battery, etc.). My concern is that instead of merely "not recommending" this solution, it is prohibited.

        Say a team is at a tournament and their MRI PDM goes out. With the rules as they stand, that team can no longer compete as most teams will have only 1 MRI PDM and few will be willing to loan any extra to another team given the perceived reliability issues that they have. Wouldn't it be better to allow that team the possibility of using a COTS hub and power splitter so they could still compete? Maybe teams will find ways around the problems you describe. Maybe teams will find that they prefer dealing with these problems over dealing with the problems they experience with the MRI PDM.

        With much of the rest of FIRST and FTC, teams are allowed to choose from a variety of solutions based on their own perceptions of their pros and cons. Is there a reason that this choice shouldn't be allowed for USB hubs and power distribution in FTC this season?

        Comment


        • Seconded. As a team, we would not have an extra PDM and would be unable to complete if it blows during a competition. I know for a fact that our PDM blew with only UNmodified batteries with original Tamiya connectors installed. I'm not sure what levels of over current protection are available as a result of the TI USB hub IC, and which are actually used.
          FTC6460 mentor (software+computer vision+electronics), FPGA enthusiast. In favor of allowing custom electronics on FTC bots.
          Co-founder of ##ftc live chat for FTC programming--currently you may need to join and wait some time for help--volunteer basis only.

          Comment


          • Or a 3D printed case to hold a right-angle connector in place.
            http://www.thingiverse.com/thing:1096699
            http://www.thingiverse.com/thing:1099628
            There are also a bunch of 3d printable strain relief designs by David Stewart available here:
            http://www.thingiverse.com/dstewartrobots/designs

            Comment


            • Originally posted by Cheer4FTC View Post
              Hi Tom,

              You say "We currently do not recommend this." I respectfully suggest that it is not just an option that is "not recommended" but instead it is an option that is prohibited by the game manual.

              You bring up various potential problems with using COTS hubs. I won't discuss the possibility that these problems could be addressed with the COTS hubs (e.g., find a way to disconnect the 5V pin, train teams to disconnect before powering off their battery, etc.). My concern is that instead of merely "not recommending" this solution, it is prohibited.

              Say a team is at a tournament and their MRI PDM goes out. With the rules as they stand, that team can no longer compete as most teams will have only 1 MRI PDM and few will be willing to loan any extra to another team given the perceived reliability issues that they have. Wouldn't it be better to allow that team the possibility of using a COTS hub and power splitter so they could still compete? Maybe teams will find ways around the problems you describe. Maybe teams will find that they prefer dealing with these problems over dealing with the problems they experience with the MRI PDM.

              With much of the rest of FIRST and FTC, teams are allowed to choose from a variety of solutions based on their own perceptions of their pros and cons. Is there a reason that this choice shouldn't be allowed for USB hubs and power distribution in FTC this season?
              Hi Cheer4FTC,

              You are correct, not only do we not recommend the COTS hub, they also are currently prohibited by the robot rules (for use in place of the PDM). I believe the rule is <RE01> part b ("The Robot Controller Android device USB interface may only connect to the Core Power Distribution
              Module.") that prohibits the use of an alternate USB hub.

              Regarding whether or not the COTS hub should be allowed, I think they are currently prohibited in part because of the technical concerns I mentioned in previous posts. You raised some good points and I will share them with the GDC and my peers at FIRST. However, currently COTS hubs are prohibited in place of the PDM.

              Tom

              Comment


              • Originally posted by hexafraction View Post
                Seconded. As a team, we would not have an extra PDM and would be unable to complete if it blows during a competition. I know for a fact that our PDM blew with only UNmodified batteries with original Tamiya connectors installed. I'm not sure what levels of over current protection are available as a result of the TI USB hub IC, and which are actually used.
                Hi hexafraction,

                I have heard your concerns and will share them within FIRST, but I cannot promise that the ruling for this season changes.

                Regarding the burned out PDM, have you contact MR about it? I think they'd like to get a look at your module to try and figure out how it got blown out.

                Tom

                Comment


                • Originally posted by Tom Eng View Post


                  In order to mitigate the chances of a blown 5V regulator on your PDM, MR recommends using the original factory Tamiya connector on the PDM and the 12V batteries.. Also, MR does not recommend that users "backfeed" power to the PDM through the Anderson Power Pole connectors on the PDM. The input power to the PDM should be fed only through the input power cable.


                  Tom
                  What will happen if the PDM is backfed? Is it just "not recommended" or will damage occur?

                  Comment


                  • Originally posted by Tom Eng View Post
                    Regarding whether or not the COTS hub should be allowed, I think they are currently prohibited in part because of the technical concerns I mentioned in previous posts. You raised some good points and I will share them with the GDC and my peers at FIRST. However, currently COTS hubs are prohibited in place of the PDM.
                    Hi Tom,

                    If you're sharing information with the GDC and others, please also share this post, posted today, which is the first reported result of a meet with the new technology. It says:
                    We had our first league meet last night with 14 teams. Three teams lost there PDM at the meet. Another team in the league lost their PDM last week.

                    Failure appeared to occur with power-on. 2 of the 3 lights on the PDM work after this happens, which indicated a problem.
                    This is not a hypothetical or imaginary problem. PDM failures are preventing teams from competing already.

                    Thanks for your consideration.

                    Comment


                    • Originally posted by aklego View Post
                      What will happen if the PDM is backfed? Is it just "not recommended" or will damage occur?
                      Hi aklego,

                      Good question!

                      I think the concern is over reverse polarity of the connectors. If the polarity of the lines feeding into 12V panel is reversed, it would damage the PDM.

                      Tom

                      Comment


                      • Originally posted by Cheer4FTC View Post
                        Hi Tom,

                        If you're sharing information with the GDC and others, please also share this post, posted today, which is the first reported result of a meet with the new technology. It says:


                        This is not a hypothetical or imaginary problem. PDM failures are preventing teams from competing already.

                        Thanks for your consideration.
                        Hi cheer4ftc,

                        Thank you for the heads up! We are definitely tracking these and other reported issues.

                        Please let me know if you are aware of additional issues or problems in the community.

                        Tom

                        Comment


                        • I modified one of my team's motor controllers as suggested by Mitch and ran a test with a robot with 2 other motor controllers and one servo controller (four controllers in all). I found that modifying the controller increased the reliability of being detected during the Robot Controller (RC) app's Scan. I posted a spreadsheet with my results at https://drive.google.com/file/d/0B3U...ew?usp=sharing .

                          Some takeaways:
                          1. If any controller was detected, the controller with the capacitor was detected.
                          2. Powering off the PDM for least 25 seconds is recommended before attempting re-scan.
                          3. Not restarting the robot controller app doesn't seem to impair finding the controllers. Powering off the PDM for 25 seconds almost always caused all the controllers to be found without
                            restarting the robot controller app.
                          4. If the Scan goes on for more than three seconds, then it will fail to find at least one controller.


                          It's possible that different test configurations would have different results, but I wanted to avoid introducing any variables by unplugging controllers. I would have like to introduce a battery with diminished charge, but I didn't have any handy.
                          John McDonnell
                          Co-Mentor, Team 5873
                          https://www.facebook.com/Team5873

                          Comment


                          • My team has been able to successfully run a fully-functioning robot, with 7 motors, 4 servos, and a gyro sensor (4 motor controllers, 2 servo controllers, and a device interface module). I have only had problems with detection of controllers 5% of the time, and this can either be solved by powering off the robot using the Tetrix switch for at least 10 seconds, or if that doesn't work, then unplugging the micro usb cable, turning off power, unplugging the battery, waiting 10 seconds, and then doing everything in reverse order. This always solves any problems the first try. Our modules are secure and our wires are moderately strain relieved, though they aren't being held in by zip ties or anything else. The only almost bad connection is the micro usb part, because that is a bad cable with a little loose connection, but when running matches and undergoing lots of forces and motion, it has not come loose, even though there are no zipties or other things holding it in place. We are able to run perfectly with no intermittent disconnects, and battery voltage does not affect the usb stuff, though it obviously has a noticeable impact on the speed of the motors. I have tried to draw lots of current by constantly switching between full forward and full reverse for the drive motors, but have never had anything happen, and we can shake around and go up and down the ramp and slam into things and still nothing happens. Even tipping ourselves over keeps everything intact. This is all with a newer PDM that we purchased 2 weeks ago from MR, because our original one was bad (only 2 leds lighting up). The new one was one we bought separately from MR, and the original PDM was the one we got in the beginning from FIRST/MR, and we finally got it replaced, though I have not tested it at all (it is our extra backup PDM). I have helped other teams, and I have noticed that powering off and unplugging the battery for 10 seconds and then also making sure all cables were secure seemed to solve every connection problem received. Let me know if you guys have any additional questions, because I have noticed the PDM to be working fine and without error.
                            Programmer for Team 4997 Masquerade -- 2012 World Champions, 2014 - 2016 Division Finalists
                            Founding Member of Team 6433 Neutrinos -- 2015 World Champions

                            Check out my intro video to the new tech platform
                            Check out my team's Robot Reveal for Res-Q

                            Comment


                            • Not sure if this has already been posted, but I was browsing the MR website and noticed this:

                              Modern Robotics Harware Troubleshooting Guide (pdf)
                              Modern_Robotics_Hardware_Troublshooting_Guide

                              Well, that's about as clear as mud, so I built a flowchart as a visual aid to this brave new world of not-really-buggy-well-OK-maybe-a-little hardware:
                              https://drive.google.com/file/d/0B5c...ew?usp=sharing

                              Hope this helps.

                              Comment


                              • Originally posted by Cheer4FTC View Post
                                ... With much of the rest of FIRST and FTC, teams are allowed to choose from a variety of solutions based on their own perceptions of their pros and cons. Is there a reason that this choice shouldn't be allowed for USB hubs and power distribution in FTC this season?
                                Wiser words could not have been spoken. Teams being "allowed to choose from a variety of solutions based on their own perceptions of their pros and cons" is the essence of FTC. Thanks C4FTC!

                                A careful analysis of ALL 173 posts in this thread shows that the PDM doesn't solve any real problems. Instead PDM injects serious problems. First and foremost the PDM a huge and unnecessary distraction to the students from robotics.

                                Tom, if I understand your posts correctly, the GDC decides how the new platform must work, and FTC Engineering must follow the GDC's direction regardless of whether or not the new platform can work the way the GDC says it must work. I think Dr. Bossi can fix these types of structural problem within FTC.

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