Re: Be aware of battery and charger inconsistencies!
 

that's the thing, it doesn't rely on maximum charge however what it does rely on is that every time u put a charged battery on the robot you expect the same performance, which our old chargers don't provide. we can make 80% charged batteries work, as long as the batteries are at the same level every time we load a new one on the robot. the key element we need is consistency. All 6 of our old chargers will charge the batteries differently and that's a major problem, every battery we put on, the kicker behaves differently and we will miss if we can't get a consistent charge level each time we start a match.

I don't get how you guys as LRI have different instructions than what all the teams are aware of. You are telling me that a 100% legal(according to every written rule) and safe robot can have the entire season jeapordised over something no one is or can even be aware of beforehand that's purely up the the inspectors discretion? that's completely insane.

"Putting a fuse inline will not help matters" why not when doing this will absolutely assure we fall within the only rule that mentions anything about it?

" Using these chargers to "top off" the battery won't work.." ummm yes they will. it's precisely what we are doing now and is all we want to do.

From the documentation all the charger does in trickle mode is set the output voltage to 13.8 and that's it. This is a very typical procedure for charging these batteries and why our other ones don't work as well i'm not sure. Perhaps it uses a different and not as effective charging method. maybe the voltage reference is off. maybe there is too much of a loss through the wire. I don't know the physics behind it and i'm not sure why but what I do know is these chargers work in the "top off" mode we want to use them in that you claim doesn't work. Buying these chargers was the investment into solving this issue. like other team's we arn't made of money so spending a few hundred dollars on new chargers simply isn't an option.

Re: Be aware of battery and charger inconsistencies!
 

You're a programmer. The #1 law of programming is...

... Computers are stupid. They do EXACTLY what you (or whoever programmed them) tell them to do.


Which means that as dumb as it may sound, it is entirely plausible that the charger doesn't quite detect that the battery is nearly fully charged and dishes out a full-power charge.


As a reminder, this rule is NOT a made-up one. It logically follows from the rules regarding battery charging in the Safety Manual.

Re: Be aware of battery and charger inconsistencies!
 

And that is where practical testing comes in, they should be easily be able to test how much current the charger puts out in this situation and see if any solution (like fusing to prevent certain currents) will work.

And while the enforcement may be based on a rule, it is not following the wording of the rule.

Re: Be aware of battery and charger inconsistencies!
 

there are a few videos in the robot showcase thread. Here is one of our autonomous mode which is not possible if we have inconsistencies with batteries: https://www.youtube.com/watch?v=mDNP...ature=youtu.be

we have a 3lb weight on the arm to have enough inertia to have enough fallow through to get the ball at the trajectory we want. even 0.2lbs heavier or lighter will reduce our trajectory. We have also played with the transmission ratios, currently those are 16:1. we tried 12:1 and it didn't have enough force to get up to speed. anything higher ratio we won't have the speed we need to get the trajectory. We thought about adding a flywheel but we run into inertia issues as with the weight. We also require a full slam to the kicker to get the ball into the goal, just a tad less and it misses. So we require a fully charged battery but more importantly each battery we put on is the same. I can move forward before I shoot but that won't solve the issue if the next battery kicks even lower then the next one super high. As you can see from its motion a stored energy system isn't really an option.

Re: Be aware of battery and charger inconsistencies!
 

It strikes me as problematic that we're essentially advocating for using the LRI's power as a roadblock to a team's participation. For many years, it's been FIRST's stated advice (e.g. at LRI training) and implied expectation that robot inspectors should do everything within the rules to permit every team to compete effectively. Although the implementation of that principle is at times complicated, I've long espoused the idea that in order to inspire confidence in the fairness of the competition, it's necessary to enforce the rules precisely, and to grant teams the benefit of the doubt when their creative interpretations of the rules lead to situations that were not envisioned by the rule-writers, even if that flies in the face of conventional wisdom.

In this particular situation, the robot rules prohibit unsafe robot systems and prescribe sanctions for violators. Concurrently, the event staff have a mandate to mitigate unsafe conditions off the field. But those are two separate kinds of authority; despite being vested in the same group of officials, those powers can't be used interchangeably, as is apparently being suggested here.

So when the rules say a team should do something, rather than they must do something, it can't be enforced as if a contravention of a mandatory robot rule. That's the case with the battery chargers that do not meet FIRST's recommended specifications: when used safely but contrary to recommendations, there's no prohibition. If there's an actual hazard, the event staff have the responsibility to mitigate it and refer it to the regional director for final resolution (particularly if the mitigation is unsatisfactory to the team). If it's an enforcement action under the robot rules (e.g. because the charger rendered a robot battery unsafe and thus illegal), then the LRI has final jurisdiction over the illegal part, but not over the charger itself.

Re: Be aware of battery and charger inconsistencies!
 

There is no need for the arguments. To summarize the issue:
The OP uses legal 6amp chargers that operate at or below their maximum of 6amps to bulk charge batteries. Afterwards, he switches to a charger that can operate at a maximum of 15amps that, according to OP, only operate at < 2-3 amps on the batteries and could prove/enforce this by putting a fuse on the charger. Appears safe, but I'm not a battery expert.

The rule in question states that batteries may not be charged at higher than manufacturer recommended specifications - (5.4, enforced at 6amps for FRC). As written, this is a limit on the process of charging, not the charger. LRIs are also on the lookout for chargers that charge at greater than 6amps at events to be deemed illegal which would include the OPs charger.

The OP is not breaking any rules in the manual BUT regional inspectors do get to make the final decision at the regional

So, if I were the OP, I would post to Q&A as you were planning to and pending their response, go ahead and bring those chargers to competition. Explain to the onsite regional inspector your setup and why you feel its legal and allow them to make the decision. Be prepared for the worst.

This guy posted this resource to help other teams, not to flaunt an unfair advantage. To negatively comment on his team's design insults everything he and all of the students on his team worked to accomplish this build season. Especially given the fact that they did consider the problem of inconsistencies in battery voltage and came up with a solution that they quite understandably think is within the rules.

Re: Be aware of battery and charger inconsistencies!
 

With the charger in question, the OP has no way to control the rate it charges his batteries. Sure, the OP could put a 5 amp fuse in series with the battery, but that still will not prevent the charger from charging the battery with 15 amps, if only for a moment.

There also are not enough resources to babysit the OP to make sure he only uses the car battery charger to "top off" - which is to say that the easiest way to enforce the rule is to disallow chargers that have higher ratings than 6A; especially chargers with ratings of 15A.


There is also a risk of catastrophe - Sure, using a healthy motorcycle battery with a car charger might shorten the life, but it won't catch fire. A big assumption in that equation is the battery is healthy. These batteries go into robots that collide with one another. The batteries are routinely discharged at very high rates, they're abused.

Using a 6A charger on a damaged battery might cause it to heat up or catch fire (I've had first hand experience with this). Using a 15A charger on a damaged battery is even more dangerous, and could cause it to explode.

Re: Be aware of battery and charger inconsistencies!
 

Which is entirely where the idea of fusing the charger came from, forcing the charger to operate less then 6 amps or not at all.

Also you wouldn't need to baby sit the team, charger has inline fuse, show to inspector that it can not charge above a certain rate because of that, inspector sees this and can go about his day. If one wanted to be paranoid they could stop by the team's pit every once and awhile and looked to see if the fuse was still there.

Re: Be aware of battery and charger inconsistencies!
 

The "easiest way to enforce the rule" is not relevant. The easiest way to enforce the rule disallowing un-inspected robots from playing is to not allow any robots to play at all, but that's not being done, is it?

Re: Be aware of battery and charger inconsistencies!
 

I do not understand what point you are trying to make, my response was to why it isn't much more work at all for an inspector to see a fuse and understand the current can not go past X for any meaningful amount of time, as opposed to the (Slighlty) easier alternative of 'no chargers with a setting above 6 amps are allowed in the venue"

Edits! Or was that in reference to efoote868 saying that it is easiest to just disallow them?

Re: Be aware of battery and charger inconsistencies!
 

I do. What he's saying is that the easy way(s) to enforce a rule isn't necessarily the right way to enforce it. Would you rather not play at all because someone was afraid of you not having passed inspection, or play?


Honestly, my opinion (utterly worthless at inspection, mind you, unless I happen to be the one inspecting you, in which case, see "Lead Robot Inspector has more say than Robot Inspector in case of disagreement"), is that if a charger is used that CAN go above 6 Amps, it should also have the ability to be SET (not auto-set, manually set) to 6A or below, and on inspection, the inspector verifies the setting and applies a tape of choice to hold it there. Auto-setting chargers that can go above 6A and cannot be set at or below 6A should, by reason of being unenforceable in terms of setting for our battery manufacturers' specs, not be permitted--but that should be made clear somewhere in, let's just say, the Administrative Manual (which, BTW, is in fact enforceable as rules*--so if it says that something or other must be followed, then that something or other must be followed).


*Enforceable does not necessarily mean enforced. Witness seat-saving, though that's getting better.

The measurement of "only 2-3 amps" was something the OP was going to demonstrate, and if it were guaranteed, I believe he could make an excellent case to the LRI. As others have pointed out, the "guaranteed" part will likely be problematic, though, unless the charger has a user-defined limit setting.

I don't think anyone is trying to insult the OP's robot design or team. He has mentioned limited resources a number of times; here are some new ones that are happy to try and help. And as someone pointed out, I suspect there will be many more at their regional who will absolutely be happy to help as well.

Re: Be aware of battery and charger inconsistencies!
 

I have just gotten off of the phone with Big Al. He is at a double regional with over 100 teams. He said he will try and respond if not today, when he gets home tomorrow. For those that do not know Big Al, he is the Head Robot Inspector for FIRST. He works with FIRST personnel and the GDC.

Re: Be aware of battery and charger inconsistencies!
 

Not to put too fine a point on it, but then you didn't design a very good mechanism. "How do I consistently control this?" is an important design criteria that mechanical and software teams need to think about when making things. It might be too late for this year but I just want to emphasize that there really is never a need to rely purely on battery consistency in FRC to achieve a repeatable result.

The next step would be to use multiple motors to run your mechanism at a slightly lower ratio. You can have more torque at a given speed this way. Combine this with an encoder or other appropriate sensor.

Understanding your limitations is important, but you have to decide how important shooting from further away is to you. There is probably a way to get there with your mechanism, with hard work, iteration, and less than "two dozen engineers". It is reasonable for one to decide that a game task is out of their reach and work around it. For example, my team won't be shooting a standing still shot from anywhere but on the goalie line for our first regional.

If your entire season relies on using a possibly illegal component to charge your batteries exactly the same way - I have a feeling that you're going to end up losing consistency even with said charger.

Re: Be aware of battery and charger inconsistencies!
 

Minor point: I think the word you are looking for is "headroom", not "overhead".