Team 781- Thanks, Congrats, and what exactly happened

[svenw]

On behalf of team 781 I would like to thank our amazing alliance partners 2016 and 177 for picking us. Not many teams know about us. In fact, very few Canadian teams are recognized on the world stage due to the difficulty of making it to the championships from a Canadian regional. This is why we were so surprised and excited that we not only made it to Championships this year, but we were able to compete on Einstein.

I know that myself and the rest of the drive team had a great time competing with you guys. It was a real blast and we have never been so excited.I don't think we slept at all during our 15 hour bus ride home, we were all too busy talking about what we had just accomplished.

2016: You guys had an amazing bot and deserved your top seed on Archimedes. Ever since I saw your unveil video at the beginning of the season I knew you guys were going to be a threat where ever you went.

177: You guys were just awesome, I now understand why your team has made it to Einstein the last 6 years in a row.

254, 111, 973: Wow what an alliance, 2 of the top scorers and 973 as defence! You guys most definitely assembled a killer alliance and it would of been very difficult to overcome you guys even if it was 3 on 3. Who knows... if we get invited to IRI this year maybe we can replay the match (losing alliance buys the other alliance a couple pretzels.)*

Last but not least I would like to thank Curtis and the rest of the field maintenance, you guys did an awesome job taping up the lines, and were great to deal with.

And to answer the question that everyone had been asking, “What happened?”. We noticed that we lost communications after the second semi final match on Einstein, the FTAs noticed that we still had communications and insisted that our Classmate had frozen up and suggested that we simply reboot it. We rebooted our classmate, tethered up and were able to operate the robot, we placed the robot on the field again lined everything up and waited for the match to start. To our surprise our robot went through the first 3 seconds of autonomous and then stopped, we sat there the entire match wondering what could possibly of gone wrong.

After the match we rushed to our robot and started diagnoses, we tethered up and had no radio signal light and no motor control(pneumatics still worked though, and we had camera feed). Our alliance called for a time out, and we were going to call in a backup if we were unable get our robot operational again before the time ran out. Because we lost everything that revolved around the sidecar we started there. I tested for any loose connections, and I redid all the wago connections to the sidecar, we tethered up again and everything seemed operational. The drive team as well as myself believed that the root cause of our problems was a wire to the sidecar which had become loose, and that we were going to be fully operational for the next match. But yet again much to our surprise our autonomous cut out in the exact same spot, this is when we knew there was something much worse that had failed with the robot.

So what happened? To be honest we do not quite know, we have theories but can not be certain. After we took our robot home on the 15 hour bus ride we started to do some diagnoses. We ran a tethered autonomous and could not recreate the problem, we ran a wireless autonomous and could not recreate the problem, we even tested our Banebots motor for any case shorting and there was none to be found. What we did find though was that if we tested for a case short while rapidly moving the arm up we achieved some interesting results, and we decided to pull the motor off. One of our mentors tore the motor apart and found that one of the leads had a loose ball of solder on it, as well as that there was evidence of debris on the commutator and brushes. So what do we think happened? The banebots motor was case shorting at a certain point, causing the sidecar to fail momentary and causing us to lose all motor control. Why were we unable to recreate this once we got home? The only hypothesis we have for this, is that the debris which was causing the case short had loosened up during the bus ride home, and no longer created a large enough short to cause a problem.


I hope this cleared a lot of things up.
Sven - team 781 captain and driver

* To those who have never played a match with 177, I must say the drive team is just a lot of fun to deal with, and don’t make any guarantees, you will owe Lyn a pretzel!

[Tristan Lall]

That's an interesting theory but there's still one thing I'm wondering: what was the return path through the sidecar? (How did the current get from battery to motor to sidecar to battery, or the reverse?)

Nice work getting to the finals. It's always nice to see Canadian content on Einstein.

[dodar]

I was rooting for you guys to come back to life, sad to see you guys lose even though you didnt get to move on Einstein. Gratz though for being the 4th Canadian team to go to Einstein!

[Chris is me]

I was rooting for you guys to come back to life, sad to see you guys lose even though you didnt get to move on Einstein. Gratz though for being the 4th Canadian team to go to Einstein!

5th. 296, 1114, 2056, 1503.

[dodar]

Oh, totally forgot about 1503 and didnt even know about 296, then that makes 781 the 6th along with 1114, 1503, 296, 188, 2056.

[BrendanB]

Oh, totally forgot about 1503 and didnt even know about 296, then that makes 781 the 6th along with 1114, 1503, 296, 188, 2056.

188 hasn't made it but it is overdue!

Congratulations 781! It was nice talking to you team in the filler line on Thursday!

[Jash_J]

Congrats again team 781!

Team 1241 Theory6 was rooting for you in the stands! You guys had an amazing run and definetly deserved it. It was an honour to work with you in Buckeye and maybe we can do it again next year! Thanks again and congrats! :D

[dodar]

188 hasn't made it but it is overdue!

Congratulations 781! It was nice talking to you team in the filler line on Thursday!

I thought 188 made it in 2009?

[thefro526]

I thought 188 made it in 2009?

Nope, they were division finalists.

[Mr. Lim]

That's an interesting theory but there's still one thing I'm wondering: what was the return path through the sidecar? (How did the current get from battery to motor to sidecar to battery, or the reverse?)

Nice work getting to the finals. It's always nice to see Canadian content on Einstein.

My theory: the return loop was a high resistance path to ground through the CIM case and robot frame. From what I recall, most CIMs demonstrate a path back to ground through the case, even though it's often a few megaohms. Measuring resistance directly between the frame and groundpost with your multimeter often doesn't show anything, but measuring voltage across +12V and the robot frame will show you +12V, proving that some kind of return path exists...

The path likely didn't even go through the sidecar, but went from +12V battery -> breaker -> +12V PDB -> Arm Speed Controller -> RS775 (Case Short)-> Robot Frame -> CIM (High Z Case to Ground) -> Drivetrain Speed Controller -> GND PDB -> GND Battery.

Some things about this theory are still fishy:

1) You won't fault unless you are running both your arm and your drivetrain at the same time. The speed controllers shunt the fault path otherwise(?). This agrees with our situation as well. Our problems only occurred when running both the arm and drivetrain simultaneously.

2) Creating a fault loop through the high resistance of a CIM case to ground path doesn't SEEM like it would cause problems... If the return path really is a few megaohms, the voltage drop caused by the fault should be negligible. Maybe someone else has a better explanation here, but my guess is that there has to be a true short from frame to ground occurring, albeit intermittent such that you would still pass inspection. I don't have our robot back from CMP yet, but would like to test resistance from the CIM case to the groundpost, both at robot rest, and when driving at full blast under load, with the CIM running. I wonder if those CIM cases do short to ground occasionally while running?

3) Both 610 and 2056 experienced very similar symptoms during the GTR, although we cut out usually for only 20-30 seconds at a time. This seemed to be in line with the time needed for a cRIO reboot. 781 cut out for the entire match. My guess here is maybe your fault had a much smaller resistance, and caused a more serious voltage drop - either in length or magnitude - causing your radio to kick over? Or the cRIO was rebooting repeatedly. That would explain losing comm the entire match, but does not agree at all with the information from the FTA, who said you retained communications the entire time... Strangely, our FTA said the same thing at the GTR, and told us to focus in on the Classmate possibly acting up. We could recreate our problem in the pits however, and clearly saw the yellow status light on our cRIO blink, indicating a cRIO reboot.

4) From 610s experience, we recorded varying resistances in the RS775 case short. As you rotated the motor, the resistances would jump around. If left unchecked, these resistances would get worse and worse the more we ran the arm. You could start the day with a non-shorted RS775, and by the end of the day, have developed a wicked short, just from running the arm in match conditions. At >200k the short didn't seem to cause any problems. Between 200k and 100k we saw drastically increased numbers of Jaguar CAN Timeouts - once every few seconds. Below 100k is when we would start seeing cRIO reboots.

5) Lastly, firmly tap the case of your main breaker a few times while running drivetrain and arm really hard. Draw as much current as you can through your robot while you do this. We had a minor issue here too, or at least we thought. :rolleyes:

Sorry to hear that this... our takeaway for next year will be to find a clever way to completely isolate the RS775s... should we choose to use them.

[craigcd]

Your team is the reason that I’m still in FIRST. You’re the reason that I believe that there will be someone to take over when my generation retires and continues to make this great program greater. I really enjoyed working with you on the Archimedes field. It was a pleasure to joke around with you guys off the field. I will keep the laser cut medallion in a place of honor on my wall of buttons from all the regionals and championships that I have worked as field supervisor. On Archimedes we had 147 matches. You guys made all that hard work fun. I’m looking forward to seeing you next year at ST. Louis.

[Al Skierkiewicz]

Guys,
The reason we watch for frame shorts is simply two reasons. The first involves robot collisions where parts of one robot contact electrical parts of another robot. Should this occur with a robot that has a short to chassis parts, the possibility exists for 24 volts to be applied to electronic parts that are not protected on both robots. We want all robots to have an ability to play in every match. The second involves robot operation. Should a frame short exist that ties the Crio frame/power common to the output of a speed controller, the possibility exists for some of the motor return current to flow through the Crio power lead. When this occurs, the Crio sees less than 24 volts at the input.
As sven has reported, there was a problem with the DSC power at some point and it is known that the RSL light was extinguished during the failure in the last match. Putting that altogether can point to a variety of problems, including a mating issue between the DSC and digital I/O on the Crio. There is also the possibility that something was shorting the 5 volt power supply in the DSC preventing output on all PWM and digital outputs. It would be interesting to know whether there is a powered sensor/pot or servo on the arm. If it is powered from the DSC, I would look for exposed wiring on the power leads going to this sensor. The power supplies in the DSC do have short circuit protection. In most cases, the short needs to be removed and the power must be reset for the regulator to come back on line. If you are using a simple pot, some fail with a short if they have been damaged internally.
Mr. Lim, the CIM resistance that you measure in most cases is the meter lying to you. It could be due to your own body, or the way that the meter measures when looking at high Z loads or even the humidity in the air or motor case. It is only resistance in the 10K or less range that concerns us.

[JesseK]

So the lesson moving forward is ... stay away from RS-775's? Of course, the assumption here is that 781's bot had the solder point/debris in a 775.

We personally didn't experience issues with the one 775 that we used, yet we also only used it during the build season. We swapped in the FP-673 for competition.

[akoscielski3]

If You remember last year in waterloo, 772 had to pull out of the playoffs becasuse of an electrical problem that was not detected. To make sure that wouldn't happen again this year we made a spair electrical board. All electrical components were mounted onto this board (except motors). To detatch the electrical board we had to remove wires from a central location(dontremember the name of it). and slide the electrical board out from the side of the chassis. Gladdly we didn't have to use it, but if we had a problem like yours, we could sawp the electrical board out to se if that was the problem, other wise it is either the programing, or other motors, or wiring. Simple to make and can save you from what happened :)

Playing against you in GTR west in the semifinals was great, but against you and 2056 we had no chance, especially with 2 other rookie teams with us:)

Good luck next year and Congrads From Team 772, Ur pit nieghbours !

[ks_mumupsi]

On behalf of 2016 I would like to say you guys were awesome to play with. We know things happen which are difficult to diagnose.

We had a similar issue in our warehouse during build season which was narrowed down to a faulty ethernet cable.. The tiniest of problems with a 4 hour head ache to fix.

I hope you guys come to IRI as we are planning on making it out there, would love to play with you again.

Otherwise see you all next year :)