TOWER Malfunctions since Week 3

[ToddF]

Having been through the Palmetto and the Virginia Regionals, I've now seen quite a few instances of "tower failures". These tend to fall into two catagories:
A) False positives that happen when a robot hits the base hard or a deployment mechanism hits the pole hard. Robots with deployment issues often repeatedly ram the tower trying to get their minibots to deploy, sometimes practically knocking the towers over in the process.
B) False negatives that happen when a minibot climbs the tower, hits the plate, but the sensors don't light. Minibots fall into two categories: direct drive bots that are very fast and light; and geared bots that use the stock Tetrix gearboxes and often stock Tetrix wheels and tend to be slower and heavier. After watching two regionals worth of matches, it is my impression (not backed up by supportable data) that all or nearly all false negatives happen to direct drive minibots. I'm sure there may be exceptions, but I'm also pretty sure there is a statistically supportable correlation.

As an engineer, I can understand that designing a sensor assembly that is sensitive enough to eliminate false negatives while also eliminating false positives may not be as easy as it first appears. But, with something as fundamentally important as an automated scoring system for a national competition, the sensors as currently designed don't seem to be fulfilling their design objectives. I'm sure they could have been designed to be more consistent, possibly by using sensor technology other than mechanically actuated limit switches. I'm also sure that they aren't going to be redesigned at this point.

We, as mentors and engineers, are now provided with a "teachable moment" for our students. Nothing in the real world is exact. Material properties, such as the yield strength of Aluminum, are generated statistically from experimental data. If you want to be absolutely positive to prevent a failure, you use allowable stresses which are well below the statistically generated averages.

We have enough observable data of the behavior of the tower sensors to conclude that their triggering threshold is somewhat inconsistent, but which could be statistically characterized if someone took the time to do so. Teams must choose to either use a heavier, slower minibot which triggers the sensor 98% (rough estimate) of the time or to use a lighter, faster minibot which triggers the sensor 70% (rough estimate) of the time. Engineers make these types of decisions everyday when designing things like cars, aircraft, and spacecraft.

We can complain all we want about the behavior of the sensors, just as we can complain all we want about how engineering materials don't break or buckle under the exact same loads every single time. Or we can teach our students how to deal with uncertainty in their design choices, and accept the consequences of those choices. As a mentor, I see my job as showing the kids how to think about the world less like a high school student (Those stupid sensors don't work right! We just got robbed! This isn't fair! Waaaah!) and more like an engineer (Now that we have observed how the sensors behave, let's make an educated choice of how best to use that behavior to make our team most likely to win.)

Todd F.
mentor, Team 2363

[MarcD79]

I think one other reason was forgotten. I witnessed minibots climb the poles @ CT Regional & strike the stationary plate bolts. We tested the trigger mechanism immediately after the round & found the tower to be working properly. We witnessed this numerous times.(Witnessed by FTA, FTAA & Head Ref with the pole directly in front of us). We all agreed that the minibots had indeed struck the bolts.

[Tom Line]

We were told in advance of MSC about the bolt issue, but neither Rush's bot nor ours is large enough to hit them.

The frustrating part for me personally is that at Troy, and at States in an earlier qualification match, our minibot hit the top plate with an audible thud. The tower lights did not change, and we were told we did not score.

In that particular elimination match, for some reason, it was ruled differently. I can only speculate that, as someone else suggested, perhaps the FMS system saw the trigger. It was all very confusing.

[ToddF]

Originally Posted by MarcD79

I think one other reason was forgotten. I witnessed minibots climb the poles @ CT Regional & strike the stationary plate bolts. ... We all agreed that the minibots had indeed struck the bolts.

Since there are published dimensioned drawings of the sensor assembly, I wouldn't consider a non-trigger due to striking a bolt to be a tower malfunction. I would consider it to be a deficiency in the design of the minibot.

Given that the bolts don't move, a properly designed minibot will avoid contact with the sensor plate in an annulus with an inner radius of 4.5 inches and an outer radius of 5.5 inches (assuming fender washers of 1 inch diameter). Otherwise you risk hitting a bolt (or washer).

Todd F.
mentor, FIRST Team 2363, Triple Helix

[Bill Moore]

Originally Posted by Jared341

At Philly, both 365 and 1403 deployed minibots that failed to trigger the tower (despite a very loud THUD at the top).

Watching the webcast on Friday (Thanks to Team 1517, the Lumberjacks), in their second match, the MOE minibot went up the pole twice and struck the plate both times. I assumed this was a deliberate change to the program to ensure no repeat of a field issue as in match #1. I found out later it was not planned, but when the minibot went back to the bottom of the tower the impact reset it. So it climbed and scored a second time.

Not a bad strategy though if you have field issues and a very fast minibot.

[Akash Rastogi]

Eventhough there is nothing we can do about it, here is the video of the tower malfunction that cost 11's alliance a spot in the finals.

http://www.youtube.com/watch?v=BvUwW...e_gdata_player

Very disappointing to watch. 11 first then 1676 then 25. Final score without malfunction was 92-91. Two regionals of being the 2nd overall Pick. Two regionals of taking the semis to 3 matches. Two straight regionals of very bad luck.

[Chris is me]

The weird thing was that 25 and 1676 lit up for second and third place, which indicates that the FMS correctly scored 11's tower as first place.

[EricDrost]

Not only did 1676 and 25 trigger as 2nd place and 3rd place, at the end of the match they were changed to 1st and 2nd place respectively, even though our minibot must have timestamped to display the other towers as 2nd and 3rd.

[Akash Rastogi]

Also, all the latest revisions of EWCP minibots were not large enough to hit the bolts. Otherwise 1477, 1323, 816 and 2415 would have all reported the same issues.

[Kristian Calhoun]

Originally Posted by Akash Rastogi

Eventhough there is nothing we can do about it, here is the video of the tower malfunction that cost 11's alliance a spot in the finals.
http://www.youtube.com/watch?v=BvUwW...e_gdata_player

Very disappointing to watch. 11 first then 1676 then 25. Final score without malfunction was 92-91. Two regionals of being the 2nd overall Pick. Two regionals of taking the semis to 3 matches. Two straight regionals of very bad luck.

Originally Posted by Chris is me

The weird thing was that 25 and 1676 lit up for second and third place, which indicates that the FMS correctly scored 11's tower as first place.

The video never shows the lights on the top of the tower that we, 25, scored on. (Chris, are you basing your statement on the linked video or something seen on the webcast?) I'm not trying to argue the outcome of the match or debate any rulings, I'm just pointing out what can be seen from the video. What's interesting is that 25 drives past 11's tower on the way back from deploying before 1676 even deploys their minibot, which had registered as second place (3 green lights). That means our minibot was already up the pole and registered as 1st place, since the blue alliance was awarded the 50 bonus points. So we can agree that regardless of how the match was scored, 1676's minibot was the last one up the pole since they were the last to deploy. Had MORT's tower functioned properly and the red alliance awarded a minibot bonus of any amount, it would have come down to the winner of the minibot race between 25 and 11. If 11 came in 2nd, then the score would have been 92-101 in favor of blue. If 11 came in 1st, Akash is correct that the final score would have been 92-91 in favor of red.

It was an extremely close match and truly could have gone either way. 25 wishes 11 nothing but the best of luck in St. Louis, both on the field and competing for the Chairman's Award. MORT has proven themselves as more than worthy contenders this year and has a lot to be proud of. We hope to finally get the opportunity to play on the same side of the field this year, either at the championships or during the off season.

[EricDrost]

That is interesting. Now that you point it out 25's minibot had to have been first/second. I believe we have a picture of it triggered as third though. I will look.

[EricDrost]

No photo of the towers but I believe 1676 also has a match video, we can check there. It's fine that we lost but I want to get to the root of the problem with the towers.

As you said, it was a very close match -- congratulations to 25/1676/1522!

[ToddF]

Team 2363 also has video of all the matches. As soon as I can get my hands on the SD cards I'll get some up on youtube.

[FRC4ME]

Originally Posted by Chris is me

The weird thing was that 25 and 1676 lit up for second and third place, which indicates that the FMS correctly scored 11's tower as first place.

Are you sure that's true? I was a volunteer doing field reset and heard the conversation between five or six Team 11 students and the referees. As an alum of 339 I was interested in the outcome. No one mentioned that 25 and 1676 had registered as second place. Had someone mentioned that, I imagine the head ref would have ruled in red's favor, as that proves that the minibot must have triggered the sensor (although the lights malfunctioned).

I don't really remember now how many lights were on. It doesn't matter now, but I guess this might be a lesson that when things don't work as planned, be as observant as possible to determine what went wrong.