Custom Chargers for backup battery

This should be a quick and easy question.

Is it legal to build one’s own custom circuitry to charge the backup battery from the main 12v battery system during the competition? FIRST distributes a rudimentary charging system schematic, but my specific question is whether or not it is legal to charge the backup battery during competition with a custom-designed battery charger.

Any insight into this issue would be greatly appreciated. I know that many teams are having difficulty with the longevity of the battery life of the backup battery. This should be one way to help out. If it is determined that it is legal, and our if team can get our design to work, I will be sure to try to post the schematics on this thread.

Michael,
<R53> The 7.2v backup battery may be charged on or off the robot. When off the robot, the battery is to be charged with the provided 7.2V backup battery charger. When mounted on the robot, the backup battery may be charged from the EX18-12 primary battery by using the custom charging circuit available from Innovation First Inc. (note: IFI will provide the design for this circuit on the IFI website, however teams must obtain the parts for this circuit and assemble it themselves)

The rule book is your friend. I suggest everyone download the manual to your laptop or shop computer. Acrobat reader has a nice search feature that helps me in finding answers quickly.

The rule on the subject of charging the backup battery:

<R53> The 7.2v backup battery may be charged on or off the robot. When off the robot, the battery is to be charged with the provided 7.2V backup battery charger. When mounted on the robot, the backup battery may be charged from the EX18-12 primary battery by using the custom charging circuit available from Innovation First Inc. (note: IFI will provide the design for this circuit on the IFI website, however teams must obtain the parts for this circuit and assemble it themselves)

It seems to say that you have to use one of the methods supplied by FIRST. However, it is not exactly clear. Try Q&A for a definitive answer.

And for the record, I don’t think we’ve ever had any longevity problems. We could run most of the day on one backup battery, partly because it was rarely used.

I was referring specifically to circuitry that was DIFFERENT from the circuit that was provided by FIRST. I have read the rule book, but felt that its position on custom circuitry for the charging of the battery was a bit vague at best. I may have to get clarification directly from FIRST on this.

I have been unable to post at the FIRST question and answer forum. Is there no one that knows whether or not we are allowed to use custom cicuitry to charge the backup battery during competition?

Your issue is with the word “may”, right? As in “[w]hen mounted on the robot, the backup battery may be charged” with the IFI device, vs. “[w]hen off the robot, the battery is to be charged” with the supplied charger. This is definitely one for the Q&A, because the intent of the rule-writer is non-obvious. Highlight (very explicitly) their choice of wording, so that the Q&A moderators don’t give you a boilerplate RTFM response. In terms of posting to the Q&A forum, your team’s main contact should have received login information by e-mail; ask them for the password to the account FRC135, or have them post on your behalf. If your main contact is not available, or has lost the information, ask here for another team to post the question for you.

Incidentally, here’s the charger circuit from IFI (which you assemble).

The issue with the word “may” does not bring into the fact of using another board than the IFI one. The word “may” is meant as you may or may not charge from the 12V battery. If you chose yes you move on in the sentence told be told you are to use the IFI board.

I concur with Steve. There is a rule written telling you how you’re allowed to charge the backup batt. If it’s on the robot, you may charge it or not. If you choose to charge it, you’re allowed to use the IFI circuit. All of the rules concerning the electrical system are very strict to keep robots from turning into short-lived arc welders. I’m pretty sure you should just assume that if they don’t explictly allow something, then it’s illegal.

I know from personal experience that the CMUcam will chew through a backup battery in about an hour. I’m not sure if the servos run off it, or if the CMUcam is actually eating up all of that juice, but the camera is almost unusable after an hour of twitching around tracking. I don’t know about you, but I’m changing the backup battery out after each match.

JBotAlan

I seem to remember the spec is 200 ma, which is a lot for a little battery pack.

i cannot seem to find this whitepaper or w/e on ifirobotics.com.
can anyone give me a direct link?
this is about the backup battery chargeing while on the robot.
thanks

It’s on the main page of ifirobotics.com under the “news or announcements” section and links to: http://www.ifirobotics.com/docs/first-backup-charger.pdf

If its only drawing 200mA, you should be able to get more than an hour off one of the IFI packs. Even with a 1A discharge, we usually get about 600-650mAh out of the packs, which is pretty good considered I believe they are rated at 700mAh.

The servo motors will run off the backup battery wether plugged into the brain, or the camera. This may be why it does not seem to last very long.

If you plug the camera from TTL to TTL serial port the camera will draw power from 5v channel on the RC which uses a 12v source.

Hate to bring up old conversation…

However at the Kokomo Workshops recently some members of other teams and i got into a discussion about wether custom charging circuits were legal.

We never really decided. However we did find that many teams had custom charging circuits on there robots and got through inspection with out a problem.

I just wanted to repost and remind every (incase i forget), that this should definitly be a question to ask this year… As it would be very beneficial to many teams.

Something a little off subject… but still partially related. I myself worked on a custom charging circuit and i do have to say that i learned a lot more by doing that then simply taking IFI’s design… I think that we should see more custom circuitry in FIRST. Because right now the way it is you learn the very very very basics of DC electrical wiring. Unless you get into custom circuits you don’t learn many things about electrical circuits and electricity as you should.

Larry,
No other charging circuits were allowed under the robot rules this year. Although I didn’t like the IFI design, teams who wanted the charger feature on the robot for the backup battery had to use the IFI circuit. I recommend purchasing an additional backup battery and a valid charger for off robot charging.
Inspectors can’t find everything so it is possible that robots made it through with chargers of their own designs.

You know, I’m still of two minds regarding this rule. And not just because I see it as being of limited utility.

Where it says “[w]hen off the robot, the battery is to be charged with the provided 7.2V backup battery charger”, it specifies that if off-robot, a certain charger is the only one permitted. But when it says “[w]hen mounted on the robot, the backup battery may be charged from the EX18-12 primary battery by using the custom charging circuit available from Innovation First Inc.”, it specifies that when on-robot, the battery may be charged by that method, but doesn’t specifically preclude another charger, as it would have if “may only” were substituted for “may” in that sentence. The implication is that this does not specify the IFI charger to the exclusion of all else, but rather that you may choose between the IFI charger or an unidentified alternative. (Steve and I argued about this during the season, and I believe that we agreed to disagree…) That would mean, that as long as the battery is “on” the robot (secured with Velcro, perhaps), it could be charged in any manner (including, obviously, the IFI charger). Maybe (indeed, probably) they meant something else, but that’s not what was written, and I don’t remember a Q&A response clarifying that intention.

As for the usefulness of the rule, it’s not as if we’re charging potentially-explosive lithium-ion batteries here; the Ni-Cd battery is a robust and relatively safe type. I’m not sure we need this rule, as written. Maybe it would be enough to require any COTS charger rated for use with the appropriate battery type and voltage.

Tris,
I believe the “may” in the language is meant that you may or may not charge the battery in the robot. If you choose to charge in the robot then the IFI charger is to be used. The issue I have with the on robot charger is that a charger with no designed in safeguards will alllow the full charge of the main battery to be dumped into the backup battery. This is a dangerous condition as all additional current will be turned into heat at the backup battery. The other problem (the one that is more likely) is that the charger will allow a sneak path for the main battery to keep circuits on the robot energized at the full potential and current of the main battery or by the backup battery alone. In either case, it gives the team a false sense of security thinking that both batteries are fully charged when they are not.

Isn’t that the first “may” in the rule? I’m considering the second one (i.e. the ninth word of the third sentence).

My point is simply that they failed to restrict alternatives (in the case of the on-robot charger) by only describing what’s allowed, and not saying what’s disallowed.

And of course, I’m pretty sure that they intended for teams to use only the IFI charge circuit for on-robot charging. It’s just that in order to say that, they should have repeated “is to be” in place of “may”, or qualified it with “only”. Sure, it’s lawyerlike to insist upon this point, but it’s also crucial to consider all the possibilities when interpreting an engineering specification.

By the way, I should qualify what I said above about COTS chargers; I meant for that to refer to off-robot charging only…