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-   -   Be aware of battery and charger inconsistencies! (http://www.chiefdelphi.com/forums/showthread.php?t=127543)

EricH 07-03-2014 22:23
Re: Be aware of battery and charger inconsistencies!
 
Quote:
Originally Posted by sanelss (Post 1355190)
I also don't see how a robot inspector can deem something illegal when he has no rules to base it off of and how the equipment you use can prevent a robot's inspection. The tools you use to maintain a robot have nothing to do with robot inspection requirements. He may state something is unnecessarily unsafe and needs to be addressed but he can't just outright deem something illegal of his own will when we can prove the opposite.
Under Section 5.5 of the Game Manual, if "Event Staff" deem something unsafe, their decision is what is followed. Robot Inspectors do count as "Event Staff"--especially Lead Robot Inspectors, who are trained by FRC Headquarters. If the LRI rules your charger is unsafe and needs to be removed from the venue, that rule right there is all that is needed, and nothing can change that. (Which is why Q&A is the proper place to ask, because that's the one thing that has a chance at changing his mind.) Incidentally, I've asked the Lead Lead Robot Inspector to weigh in on this discussion, bearing in mind that anything posted here is unofficial.

Quote:
I know i'm being stubborn, both because our season depends on it and because i honestly don't think we're in the wrong. If it wasn't such a critical thing I would just let it go but it's not something we can just let go without having a dramatic and devastating effect on us. It's either we can use these for trickle which is within all rules, or we can't do 3 ball autonomous and we will probably miss most shots because of battery inconsistencies.
If you hadn't been absolutely positive that you were legal (which you are now finding that maybe you shouldn't have been so positive--it never hurts to ask questions earlier), would you have chosen the same path in design?

There's a reason the field sizes are given with a tolerance--expect variations to happen. One thing a number of longtime veterans have learned is that the specs given are not necessarily totally exact. Case in point, the balls have been noted to behave differently at competition than at a lot of team facilities, for reasons unknown. Maybe you don't quite need full power to shoot as far as you want to--but you won't know that for sure until practice matches.

Quote:
So our two options are find a way to use these, or give up hope on doing well this season since we know full well we can't perform if we can't use something better than our old chargers. I don't think i'm doing anything different than anyone else would.
Wrong. You have a third option: Adapt. For example, I don't know anything about your robot, other than that it's a "kicker" type. I know you've tried a bunch of variables--have you tried a smidge more weight, strategically placed? What about different tip surfaces? Slight change in geometry? You have all day Thursday with the practice field and the pit and the event machine shop and the combined resources of however many teams are there and as many inspectors as opt to give advice--if a competitive robot can be built in less than 8 hours at an event, why can't a robot that doesn't quite have the adaptability it needs gain that adaptability? I might also note that if you have a tough drivebase, you can probably play some pretty tough defense or counter-defense, which can make you an attractive alliance partner.

cgmv123 07-03-2014 22:26
Re: Be aware of battery and charger inconsistencies!
 
Quote:
Originally Posted by sanelss (Post 1355190)
As someone mentioned we can fuse it for 6A and that should remove all doubt from our situation and fallowing rules. From the previous linked documentation there is absolutely no danger even if it were to charged at 15A with these chargers, there simply is no safety risk other than a couple people's fear of what they don't have knowledge of. Well no more safety risk than any other charger that is. This is not a valid reason to restrict equipment when there is information showing it's perfectly reasonably safe.
Fuses do not limit current. A 6 amp fuse can and will pass current in excess of 6 amps. It's been well stated that the FRC Safety Manual says to not charge in excess of 6 Amps.

Quote:
I also don't see how a robot inspector can deem something illegal when he has no rules to base it off of and how the equipment you use can prevent a robot's inspection. The tools you use to maintain a robot have nothing to do with robot inspection requirements. He may state something is unnecessarily unsafe and needs to be addressed but he can't just outright deem something illegal of his own will when we can prove the opposite. Or maybe they have some secret powers i'm not aware of.
Quote:
Originally Posted by FRC Game Manual
At each event, the Lead ROBOT Inspector (LRI) has final authority on the legality of any COMPONENT, MECHANISM, or ROBOT. Inspectors may re-Inspect ROBOTS to ensure compliance with the rules.
Quote:
Originally Posted by T6
A Team is only permitted to participate in a Qualification or Elimination MATCH and receive Qualification Points if their ROBOT has passed Inspection. If it is discovered after the start of the MATCH that a ROBOT did not pass Inspection and the Team participated in the MATCH, the entire ALLIANCE receives a RED CARD for that MATCH.
I would strongly advise not going against the LRI. You won't win. Not just anyone can be a Robot Inspector, especially a Lead Inspector. LRI's, especially Big Al, who is the Lead Inspector of Lead Inspectors, have been in FRC for a long time and know what they're talking about.

Quote:
I know i'm being stubborn, both because our season depends on it and because i honestly don't think we're in the wrong. If it wasn't such a critical thing I would just let it go but it's not something we can just let go without having a dramatic and devastating effect on us. It's either we can use these for trickle which is within all rules, or we can't do 3 ball autonomous and we will probably miss most shots because of battery inconsistencies.
Working within parameters is part of engineering. You had a specification that was given to you from the beginning of the season. Unlike many of the other rules, this one hasn't changed since I've been in FRC (2011). Successful teams will design robots that are impervious to as many outside factors, including battery charge.

Quote:
So our two options are find a way to use these, or give up hope on doing well this season since we know full well we can't perform if we can't use something better than our old chargers. I don't think i'm doing anything different than anyone else would.
You can modify your robot to account for the different battery characteristics. It's part of the engineering process.

wireties 07-03-2014 22:30
Re: Be aware of battery and charger inconsistencies!
 
Quote:
Originally Posted by sanelss (Post 1355086)
So dremels, grinders, and etc also shouldn't be used either because they have the potential to cause sparks and catch something on fire? Drills and other power tools shouldn't be used either because someone may get injured? this is complete nonsense. A properly used battery charger is no different than a properly used dremel. And so long as all rules are fallowed, safety ones included, there shouldn't be arbitrary limitations. Is there also speed limits for robots? because you know that just isn't safe. Robot's shouldn't be allowed to be powered on in the pit either, because of course you know something might happen and it's a confined space. There is common sense, then there is going to unnecessary and unwarranted extremes.
There is no need to get hysterical. You can follow advice from experienced FIRSTers and in my case 30+ years engineering experience OR you can ignore the advice and take your chances with the inspectors. It is always your choice.

The safety manual (quoted by others in this thread) limits many of your examples. Of course there will always be safety risks but some risks can be eliminated.

Let me make a constructive suggestion - why not drive forward a couple feet then shoot? It solves all your problems. You can't do a 2-ball autonomous anyways if one kick sucks the top end out of your battery.

Take a deep breath, solve the problem without risking the inspector's ire and good luck to you and your team!

wireties 07-03-2014 22:34
Re: Be aware of battery and charger inconsistencies!
 
Quote:
Originally Posted by sanelss (Post 1355190)
I also don't see how a robot inspector can deem something illegal when he has no rules to base it off of and how the equipment you use can prevent a robot's inspection. The tools you use to maintain a robot have nothing to do with robot inspection requirements. He may state something is unnecessarily unsafe and needs to be addressed but he can't just outright deem something illegal of his own will when we can prove the opposite. Or maybe they have some secret powers i'm not aware of.
It may or may not be fair but you are DEAD wrong here. The LRI is the safety god for that weekend. Nothing one can say will change that.

You are talking about exposing your team to a huge risk. I can't caution you enough.

Good luck!

Nirvash 07-03-2014 22:44
Re: Be aware of battery and charger inconsistencies!
 
Quote:
Originally Posted by cgmv123 (Post 1355197)
Fuses do not limit current. A 6 amp fuse can and will pass current in excess of 6 amps. It's been well stated that the FRC Safety Manual says to not charge in excess of 6 Amps.
A quick google search and looking at a fuse spec sheet later show that a 5 amp fuse will open in 2 seconds if exposed to a 6 amp current (For that model of fuse), while this does not 'limit' current, it does stop any flow of current if the level of current goes higher then rated for more then two seconds.
I don't see how any unsafe behavior can occur in that time.

And on another note, how many people have checked to see how many amps their chargers put out? Manufacturing tolerances do exist, and that 6 amp charger (which is already 'breaking' the rules) may put out slightly more.

If this enforcement of the rule was following the rules wording properly all chargers that have a 6 amp setting should not be allowed as they will go above the max charging current of 5.4 amps.

cgmv123 07-03-2014 22:49
Re: Be aware of battery and charger inconsistencies!
 
Quote:
Originally Posted by Nirvash (Post 1355201)
A quick google search and looking at a fuse spec sheet later show that a 5 amp fuse will open in 2 seconds if exposed to a 6 amp current (For that model of fuse), while this does not 'limit' current, it does stop any flow of current if the level of current goes higher then rated for more then two seconds.
I don't see how any unsafe behavior can occur in that time.
I don't see how any unsafe behavior can occur in 2 seconds either, but I also don't see how a 10+ Amp charger will know that there's a 5 amp fuse and limit its current. You'll just blow the fuse every time you try and charge a battery.

sanelss 07-03-2014 22:51
Re: Be aware of battery and charger inconsistencies!
 
Quote:
Originally Posted by EricH (Post 1355196)
If you hadn't been absolutely positive that you were legal (which you are now finding that maybe you shouldn't have been so positive--it never hurts to ask questions earlier), would you have chosen the same path in design?
Yes because it's not the design that's in question. honestly we never imagine this would be an issue since we went through all rules and found no mentions. Even with the 6A rule it didn't bring the certainty into question either because we can easily abide by it. We know factually that we fall within all rules, so these claims that even though we know we are 100% completely legal yet run into the possibility of having something happen like this of something that isn't written down anywhere(like chargers over 15A being illegal according to the LRI) is absolutely ridiculous. It's a rule that's not stated as a rule. we worked within all constrains but now we find out that there are these other secret rules? what the hell that's completely unacceptable.

Quote:
Originally Posted by EricH (Post 1355196)
There's a reason the field sizes are given with a tolerance--expect variations to happen. One thing a number of longtime veterans have learned is that the specs given are not necessarily totally exact. Case in point, the balls have been noted to behave differently at competition than at a lot of team facilities, for reasons unknown. Maybe you don't quite need full power to shoot as far as you want to--but you won't know that for sure until practice matches.
we may not, and that would help a lot, but until that moment we won't know and we will be counting on needing full power. But again the issue isn't the voltage they charge up to, it's the consistency that matters to us. If we have to be closer to make it fine, but when we do a battery swap currently the shots we made previously don't go in anymore, this is the issue i'm talking about. They are either too high or too low.


Quote:
Originally Posted by EricH (Post 1355196)
Wrong. You have a third option: Adapt. For example, I don't know anything about your robot, other than that it's a "kicker" type. I know you've tried a bunch of variables--have you tried a smidge more weight, strategically placed? What about different tip surfaces? Slight change in geometry? You have all day Thursday with the practice field and the pit and the event machine shop and the combined resources of however many teams are there and as many inspectors as opt to give advice--if a competitive robot can be built in less than 8 hours at an event, why can't a robot that doesn't quite have the adaptability it needs gain that adaptability? I might also note that if you have a tough drivebase, you can probably play some pretty tough defense or counter-defense, which can make you an attractive alliance partner.
We tried everything at our disposal. Different transmission ratios, different speed controllers, different weights(in different locations),different kicker geometry, even different kicker transmissions types(from worm to bewel). Believe me when I say if it was within our capability we would have. We knew from the start it would creep up as an issue, and thought that getting good chargers was the fix.....what you said sounds like an absolute dream: "combined resources of however many teams are there" but that's not reality. There is nothing wrong with our kicker or robot, it's our chargers. all we want is a consistent charge, that's all and we thought we found the fix for that. Just like all the other things people mentioned saying stuff like this is easy, but actually doing it is a much different story esp considering the resources(in our case lack of). It sounds great on paper, but has no real basis in reality, at least from my own experiences.

sanelss 07-03-2014 22:55
Re: Be aware of battery and charger inconsistencies!
 
Quote:
Originally Posted by cgmv123 (Post 1355204)
I don't see how any unsafe behavior can occur in 2 seconds either, but I also don't see how a 10+ Amp charger will know that there's a 5 amp fuse and limit its current. You'll just blow the fuse every time you try and charge a battery.
because it will never be in that state. when these chargers are used for trickle it will never draw more than a few amps. just because it can output 15A doesn't mean it will. I would be suprised if they output more than 1-2A in trickle and we'll put a 3A fuse on it in that case. The point is we can PROVE we don't break any rules yet this doesn't seem to be enough for these people.

Nirvash 07-03-2014 22:56
Re: Be aware of battery and charger inconsistencies!
 
Quote:
Originally Posted by cgmv123 (Post 1355204)
I don't see how any unsafe behavior can occur in 2 seconds either, but I also don't see how a 10+ Amp charger will know that there's a 5 amp fuse and limit its current. You'll just blow the fuse every time you try and charge a battery.
It would be very dumb for a smart charger to give a nearly fully charged battery 15 amps, the charger in question may, I don't have one and have no way to test that, but the fuse would ensure the charger falls on legal grounds.

Mr V 07-03-2014 23:53
Re: Be aware of battery and charger inconsistencies!
 
Do yourself and your team a favor and leave those chargers at home. If the robot's performance depends on an absolutely fully charged battery then invest in some high quality chargers that will pass the scrutiny of the LRI.

You keep saying that your season depends on using these chargers. As an LRI I say your season is in jeopardy due to bringing these chargers in the door.

Putting a fuse inline will not help matters. Using these chargers to "top off" the battery won't work unless you have either given them time for the surface charge to dissipate or you put a load on them to remove the surface charge. Option one means wait several hours minimum to charge and putting enough load on it to remove the surface charge quickly and consistently means that the starting charge rate of the charger will likely blow the fuse.

kevin.li.rit 07-03-2014 23:57
Re: Be aware of battery and charger inconsistencies!
 
Quote:
Originally Posted by sanelss (Post 1355205)
We tried everything at our disposal. Different transmission ratios, different speed controllers, different weights(in different locations),different kicker geometry, even different kicker transmissions types(from worm to bewel). Believe me when I say if it was within our capability we would have. We knew from the start it would creep up as an issue, and thought that getting good chargers was the fix.....what you said sounds like an absolute dream: "combined resources of however many teams are there" but that's not reality. There is nothing wrong with our kicker or robot, it's our chargers. all we want is a consistent charge, that's all and we thought we found the fix for that. Just like all the other things people mentioned saying stuff like this is easy, but actually doing it is a much different story esp considering the resources(in our case lack of). It sounds great on paper, but has no real basis in reality, at least from my own experiences.
Have you tried a variable transmission ratio to maximize your speed/acceleration? Anyway to store some energy in your kicker first?

MrBasse 07-03-2014 23:57
Re: Be aware of battery and charger inconsistencies!
 
Quote:
Originally Posted by sanelss (Post 1355205)
... the issue isn't the voltage they charge up to, it's the consistency that matters to us. If we have to be closer to make it fine, but when we do a battery swap currently the shots we made previously don't go in anymore, this is the issue i'm talking about.
...
Wha is your plan if you get into eliminations? Do you have 6-8 batteries that are all the same age/capacity/health? There likely won't be enough time to fully recharge if you don't.

I can vouch for the don't argue with the LRI concept. Even if they find out they were mistaken, you will still have to make them happy in order to compete. Changing things to keep the inspector happy is no fun at competition.

sanelss 08-03-2014 00:11
Re: Be aware of battery and charger inconsistencies!
 
Quote:
Originally Posted by kevin.li.rit (Post 1355221)
Have you tried a variable transmission ratio to maximize your speed/acceleration? Anyway to store some energy in your kicker first?
a variable transmission isn't within our capabilities at this point. Considering our kicker does continuous 360 an energy storage system would be extremely difficult as well.

Nirvash 08-03-2014 00:13
Re: Be aware of battery and charger inconsistencies!
 
Quote:
Originally Posted by MrBasse (Post 1355222)
I can vouch for the don't argue with the LRI concept. Even if they find out they were mistaken, you will still have to make them happy in order to compete. Changing things to keep the inspector happy is no fun at competition.
Just my stupid personal opinion, but one should not have to make a LRI 'happy' by following a made up rule.

The rules in question do not state the max rating of a charger, but the max rate you charge at.

kevin.li.rit 08-03-2014 00:17
Re: Be aware of battery and charger inconsistencies!
 
1 Attachment(s)
Quote:
Originally Posted by sanelss (Post 1355226)
a variable transmission isn't within our capabilities at this point. Considering our kicker does continuous 360 an energy storage system would be extremely difficult as well.
Well I don't know what your robot looks like and at this point I think we'd all like to see. But its really simple, Have you tried the attached idea?


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