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  • Drop, Drop, Drop

    Two weeks ago in our Qualifier we completed and won 10 matches in a row with zero problems. Today in our State Competition we drop Samatha in 6 straight matches thus making a very bad day. I am very aware of wiring issues, mounting issues, connector issues and we have dealth with all of that. Today out of desperation we changed the Samantha, power switch, NXT, re-flashed the Samantha, changed the usb cable. The Samantha is wired right after the switch from the 12v battery. All connections are soldered. In testing mode with the Pit Router the robot is put through it's paces physically with NO issues. On the next match we drop wifi ... 6 matches in a row. A few other teams had wifi issues but in general most teams did not. There is a tendency to drop wifi when we bump and/or stall motors but NOT in all cases. Sometimes after 10-30 sec the wifi will reconnect and we can continue. We start each match with a fully charged battery. I am an Electronic Engineer and I think a pretty good troubleshooter but this problem has become challenging. I am thinking a draw down of the 12v or a surge might be causing the problem but I can't prove that is happening.

    Of course, I am open to any and all suggestions. I have done alot so far but the problem still exists. Please let me know if you had a similar problem and what solution was used. Even though we are now out I would like to know what is happening. Thank you.

    Ray

  • #2
    Do you know if your nxt froze up at all? We have had only one drop out this year and it was because our nxt froze up. Also make sure that all your software is up to date as well.

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    • #3
      Sadly this problem plagues many teams. Even in the semis and finals at worlds you sometimes see problems like this arise.

      Static electricity problems can often cause issues like this. Particularly you can see it during bumps if a static surge is transferred from one robot to the next. Sometimes you can have great success on a day where there's enough humidity in the air (high enough temperature, rainy day, etc.) and then go to the next tournament on a cold dry day and have nothing but problems. The Cougar Robotics team has gone to great lengths to address these as much as possible with conductive tape, wipes that dissipate static, and even suggesting measures that minimize static for event organizers (with humidifiers, mist sprayed over the field during matches, field floors wiped with anti-static wipes, etc). You might want to check out this link for some ideas:
      http://www.instructables.com/member/...=INSTRUCTABLES

      Look in particular at their video on their static electricity detector and how their conductive tape has minimized the issue to some extent.

      Some teams at worlds also went out of their way to provide insulation against exposed metal parts so that a robot-to-robot bump wouldn't result in a large static surge from one robot to the other. If you see a team with lots of tape over all of their exposed metal (even the screws on the wheels!), that's why they're doing it.

      Drop outs can also happen if many motors are stalled causing big current surges, though it sounds like you've done what you can with respect to having the samantha wired right off the battery.

      I share your frustration. After a team has worked so hard for so long to be successful, there's nothing worse than attending a tournament where their robot just doesn't work like it should. I truly wish FIRST and FTC would work on a long term strategy for rock-solid FTC communications hardware and software so the kids can focus on robot design and not ways of working around communications issues.

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      • #4
        Here's also a good video from the Landroids showing a static discharge problem, particularly when one robot is on wood (like the bridge this year) and the other is on the mat building up a charge.
        http://www.youtube.com/watch?v=Rr4mBtiYmjs

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        • #5
          Hey Ray,

          I was the short FTA constantly running around and restarting robots and I can say that yours actually performed better than most in that regard. I was very impressed with your team's robot this year--great job team.

          During many of the early qualifying rounds, the problem appeared to be the cable connecting the NXT to the Samantha module. Whenever this is the case, the wifi light on the brick blinks as well as the blue NXT light. Whenever I see the blue NXT light blink and then go solid, there is nothing to do but wait for the wifi to reconnect. I think I may have stopped and restarted your Teleop once, but I honestly don't recall. (Note: they don't typically fix NXT cables or any loose wires at World or any higher level tournament. I fixed these issues midround because I hate to see a team just sit there not being able to do anything.) Occasionally, the NXT light would not start blinking to indicate the NXT had disconnected, but the "usb" indicator would not be present. I can only see the "usb" text in the NXT statusbar so I can only check this between rounds or while trying to get a robot to connect before a round. Instead of saying "usb," there was an image of a cable. Speaking not from technical knowledge but from experience, whenever the cable image was visible, the blue NXT light would be on, yet there was no communication from the NXT to the Samantha. I likened it to when you plug a flash drive into a computer and it says "Device not recognized" but it still sends the device power, lighting up the flash drive access indicator.
          However, this seemed to be the case on teams that had their NXT usb port pointing toward the outside of the robot where it could easily flex and damage the internal pins on the brick. I know that one team had a great deal of trouble connecting over the FCS and their NXT usb port was positioned such that any impact to that side of their robot would hit the cable. I don't recall the construction of your robot, but I doubt that was the case with your team (you probably know better).

          I know that probably doesn't answer your question, but I do hope it provides some insight into what was happening on the field. If you connect the Samantha to your brick and find that the text that says "usb" can be changed to the wire image by jiggling the cable, the NXT brick itself could be the problem. When first plugging the cable in, it will sometimes show the cable image briefly and I haven't determined if that is the connection initializing or if that is another symptom of this issue. (Lego will sometimes replace this sort of thing for free. The screen on my personal NXT died last year and they sent me a brand new brick.)

          Static was not a problem at this tournament because the field was sprayed with anti-static spray. This is why many teams' scoops or lifts that slightly touched the ground kept getting "caught" on the mat. It likely wasn't poor design, just the anti-static spray that leaves a sticky residue causing the robot to hop rather than glide. I can also say that static wasn't an issue because no bricks were locking up, which usually does happen during a static discharge.

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          • #6
            I do not think the NXT froze up as WiFi often reconnected. Some comments below from System42 who was one of the FTA's.

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            • #7
              It could have been static but I really don't think so as the field was anti-sprayed. Connections are the likely problem but I am confident we dealt with all of them. We put the robot through some pretty rough moves in anticipation of connection problems. Stalls and surges are likely since some of the drop connections occurred after some physical contact. However, many stalls and collisions have occurred not only at home but in the last Qualifier where we had no issues. I will check out the provided link. For the first four matches I had two ground wires from the chassis to the mat and one ground from the battery to the chassis. Removed them on the last two matches with no difference.

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              • #8
                Good video. Shows the problem of static.

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                • #9
                  I am sure the problem is with the way we mounted or connected the Samantha. I was going by what I found as a recommended method. Several have emailed other suggestions and I appreciate the input.
                  Last edited by FTC5963; 02-10-2014, 01:24 PM.

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                  • #10
                    System42, Thanks for your feedback. I was very aware of the effort you made with our problem. It was very much appreciated. What other kinds of drop problems did you witness during the competition?

                    Ray

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                    • #11
                      I think part of the issue may stem from the high torque and power demand the new v2 motors are capable of producing. When the new v2 motor is ran near maximum power it's running at I believe 2x the power supplied to the old motor. I can't imagine the motor controllers and other electronics are designed to cope with this.

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