Team Update #18

[JB987]

Originally Posted by colt527

I am not apologizing for FIRST, I am just advocating pragmatism from the teams. The bolt pattern was definitely not obvious and I don't remember seeing it anywhere in the official rules. They are in the official field drawings in sections 37, 38 and 69 of the Game Field Elements but I know most teams (including my own) don't check those.

Believe me I sympathize with any team who's bot successfully climbs the pole but doesn't get the points for it. I know that it must be immensely frustrating. I want to eliminate that from ever happening. Thats why I think that with a few small minibot modifications, this will become simply a non-issue and the tower results will match everyones expectations.

I know there were cases where the minibots reached the top of the tower but it didn't trigger. I am just being honest and did not see any of those cases where it was completely obvious that the bolt was not hit and that it delivered enough force and still did not trigger.

I have tried several times this evening to access the tower diagrams and get timed out waiting for the download...does anyone have a stored image of the top plates and the bolt pattern they can share?

[MrForbes]

This is what it's all about:

TRIGGERED – the act of pushing the bottom disk of the TARGET so that the sensors are tripped and a signal is sent to the Field Management System (FMS). When a TARGET is TRIGGERED, the MINIBOT RACE on that TOWER is complete.

You gotta TRIGGER the TARGET. If your minibot doesn't TRIGGER the TARGET reliably, you might need to redesign your minibot.

The description of the ARENA suggests that it will take a minimum force of 2-4 Newtons to TRIGGER the TARGET.

[Karibou]

Originally Posted by JB987

I have tried several times this evening to access the tower diagrams and get timed out waiting for the download...does anyone have a stored image of the top plates and the bolt pattern they can share?

I don't want to attach/upload/etc the full field elements document, but I took a screenshot of the drawing of the bottom plate, which is where it seems that the bolts are an issue. Page 69 of the 2011 Game Field Elements_RevA, if you manage to download it and view it yourself.


Edit: You can see the bolts in some of Dan Ernst's pictures: http://www.flickr.com/photos/daniele...7626138552781/, http://www.flickr.com/photos/daniele...7626138552781/, http://www.flickr.com/photos/daniele...7626138552781/

[s_forbes]

Simple solution: remove off switch, replace components as needed.

Originally Posted by Ether

How much does a 12" diameter 0.25" thick polycarbonate plate weigh? My quick calculation says it's more than 4 Newtons (please check my math). So obviously 4 Newtons is not enough force to move the plate at all, let alone violently accelerate it. So where did the 2-4 Newton number in the manual come from?

This is an interesting point that never crossed my mind. Quick math suggests about 4-5 newtons of force just to cancel out weight of polycarb plate. Someone should bring a scale to one of this weeks competitions and see how much force is actually needed to trigger the plate (ignoring impulse). Might lead to some exciting discussions with the refs!


This week is going to be fun.

[MrForbes]

The rules don't say you need to hit the plate with 4 N force to win the race. They say you need to trigger the tower.

Isn't that the way it's been all along?

[Cory]

Originally Posted by s_forbes

Someone should bring a scale to one of this weeks competitions and see how much force is actually needed to trigger the plate (ignoring impulse).

Good luck. Ever try asking to measure the overpass height in 08 to confirm it was within the tolerance listed?

Originally Posted by squirrel

The rules don't say you need to hit the plate with 4 N force to win the race. They say you need to trigger the tower.

Isn't that the way it's been all along?

And to trigger the tower you need to hit it with 4N of force. Your argument seems sort of circular? If you hit it with 4N of force and it doesn't trigger, then FIRST failed to implement their triggering solution correctly.

[Tristan Lall]

Originally Posted by squirrel

You gotta TRIGGER the TARGET. If your minibot doesn't TRIGGER the TARGET reliably, you might need to redesign your minibot.

The description of the ARENA suggests that it will take a minimum force of 2-4 Newtons to TRIGGER the TARGET.

Exactly: by definition, if the sensors aren't tripped, you haven't triggered it, and are entitled to zero points. It doesn't matter how hard you hit it.

Fundamentally, the problem is that the rules define scoring in terms of a process that is hard to directly observe (were the switches actually tripped, or did it hang up on the bolts?), and which is inherently impractical to error-proof (did the sensors get tripped because a robot shook the tower, or because a minibot ascended it properly?).

When the refs were scoring it manually, there was really no way for them to systematically and conclusively distinguish false positives, false negatives, true positives or true negatives. They were just guessing. (And the timing aspect being based on triggering, and not mere contact made it all the more impractical to observe from floor level.)

I think this update makes the best of a game design choice that was, in retrospect, not so good. An alternative might have been a rule change, to change the criteria for triggering, but I can certainly see that that introduces other problems. I can only hope that FIRST did some testing and established that the best balance of true and false outcomes is achieved through the changes they've implemented.

[MrForbes]

Originally Posted by Cory

And to trigger the tower you need to hit it with 4N of force. Your argument seems sort of circular? If you hit it with 4N of force and it doesn't trigger, then FIRST failed to implement their triggering solution correctly.

My argument isn't circular. You're hung up on the 4N number. The game rules don't mention it. The ARENA description does, but it does not say that it's an upper limit. It suggests it's a lower limit.

You've been in FIRST long enough to know that the ARENA doesn't always behave the way the manual suggests that it might.

I guess we'll find out in a few days how our minibot does. I expect we'll probably have to play with the off switch, if we can get it to deploy legally. Should be interesting.

[sanddrag]

So, do you really need to hit it for 75 milliseconds!? That seems like an awfully long time. And what about issues such as switch bounce. Is that dealt with?

[Chris is me]

Originally Posted by squirrel

The ARENA description does, but it does not say that it's an upper limit. It suggests it's a lower limit.

I think you're reading it wrong. I read it as "the minimum force is 4n" as in "any force 4n or above will trigger".

I think first saying "lalala our sensors are perfect" and ignoring teams is just stupid myself.

[WizenedEE]

Well, switch bounce wouldn't matter, because you can't score twice on the same tower. Switch bounce just makes it look like there was a bunch of hits when there was actually only one.

[Tristan Lall]

Originally Posted by Chris is me

I think you're reading it wrong. I read it as "the minimum force is 4n" as in "any force 4n or above will trigger".

The manual says that "[a] minimum contact force of approximately 2-4 Newtons, depending on contact location, is required to ensure the contact sensors in the TARGET trip reliably."

I don't read that as a definition; to me, that looks like an observation for the benefit of the teams. If it were a definition, it would be the worst definition in the world. (Approximately? A range of force? Depending on contact location? And how do you quantify "reliably"?)

[Chris Hibner]

Originally Posted by squirrel

My argument isn't circular. You're hung up on the 4N number. The game rules don't mention it. The ARENA description does, but it does not say that it's an upper limit. It suggests it's a lower limit.

Here's my issue: if they only specify a minimum, then how to you guarantee you trigger the sensor? If my minibot applies 1000 N and it doesn't trigger in a match, then that is perfectly acceptable field behavior by the definition in the rules as you interpret it (however ludicrous that is).

As an engineer, I expect specifications that are guarantees of proper performance - not a specification of "below X it's guaranteed to not work, and above X may or may not work but we're not really sure". With no specification of "above XX N the tower WILL trigger" how do we design minibots?

Can't the silly force triggers be replaced with light sensors or proximity switches? Those won't be fooled by robots bumping into the bases, won't have different properties depending on where you hit the plate, and won't bind on the pole like I've seen the plate do.

[Josh Fritsch]

Easy way to know if your minibot will be ok? Have a FIRST certified tower during minibot inspection with a force gauge on it. Then you can have a document from an inspector stating that your minibot meets the minimum required force needed to trigger the target. So if it doesnt happen on the field you have some sort of justification for the refs.

This would eliminate everyone on here saying "show me the calculations to prove it!" or "you didnt account for this drag force or weight of the plate!" etc...

[Vikesrock]

Originally Posted by squirrel

My argument isn't circular. You're hung up on the 4N number. The game rules don't mention it. The ARENA description does, but it does not say that it's an upper limit. It suggests it's a lower limit.

I guess we were all hoping that the 4N spec was an attempt to provide a specification that teams could test or at least calculate and know where they stood.

Even if you build a competition tower exactly according to the Game Drawings you cannot test TRIGGERING at home because you don't have the FMS setup. That's not an engineering challenge, it's a lottery.