Capacity of backup battery?

Technical Electrical
1

I can’t seem to find out what the capacity of the supplied backup battery is.
I have a much better charger than the one supplied but an important piece of info is how much capacity the pack has or it might cook it.

Also, am I limited to NiCd or is NiMH OK too? We are running AndyMark SuperShifters with servos and a large NiMH pack would really be a lot better!

As for commercially available replacements, I can’t seem to find anyone who makes packs with that type of connector.

Help!

Thanks in advance,
–Mark:ahh:

2

R73 : “As a replacement for the FIRST-supplied battery, any other commercially available 7.2V NiCad battery pack may be used.”

R49 : “When off the ROBOT, the battery is to be charged with a 7.2V backup battery charger. When mounted on the ROBOT, the backup battery may be charged from the 12VDC primary battery by using the custom charging circuit available from Innovation First Inc. or any similar charging circuit (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 use of this circuit is strongly encouraged.”

Now, these quotes are from Rev A of the rule book, so you may want to double-check the Q&A forums and go re-read the rules yourself, but unless these rules have changed, or I have missed something:

A) The first and best option is to build/buy the on-robot charger that tops up your backup battery from the main battery. You will never run out of power for your servos unless you run out of power for the whole robot… which just doesn’t happen in a two minute match.

B) “any other commercially available 7.2V NiCad battery pack may be used” seems pretty clear… it makes absolutely no mention of a MAh capacity, and FIRST is quite good in supporting the rules as they are written (and updated in the Q&A)

C) If you are using any kind of fast charger for a NiCad, I highly recommend you use a peak detection charger which will determine when the batteries are charged. If you are worried about charge RATE, which depends on both the battery capacity AND charging speed (some NiCads can be fast charged, cheaper ones not so much) then I suggest you contact IFI directly. IFI Robotics also maintains forums where you can ask the technical experts who build this equipment these quesitions.

But check out that answer “A” option… it seems your best bet.

Jason

3

Thanks Jason.
I do have peak cell detection and could probably use that but it’s always nice to know the capacity so you can tell if you have a bad cell etc…
The problem with commercially available packs is the connector. Most manufacturers are using the Tamiya or Deans type connectors. The connector type use by IFI is extremely hard to find.
I’ll touch base with IFI and see what info I can get from them.

I guess NiMH is out of the question. Too bad. I like the idea of being able to “top charge” without inflicting the dreaded NiCd “memory” effect.

–Mark :cool:

4

Now that I notice your user name, I’m not surprised you are looking at battery options! Some Li-Poly would be nice, no?

I have not found any rule stating that the connector used on the battery is a required part, nor any reason why you couldn’t lop off the connector and replace it with a Dean’s or something more standard. Before I made any modifications, however, a quick question to the Q&A would clarify things.

Jason

5

I saw this go by in the Q&A…

Q&A Section 8 The Robot > Power Distribution > Alternate backup battery?
http://forums.usfirst.org/showthread.php?t=8282
Q:
Is a different 7.2v backup battery allowed for use on the robot?

Is an alternate connector for this backup battery allowed?

A:

  1. Yes. Please see Rule <R73>.

  2. No. This would be prohibited by Rule <R67>.

6

I went back and re-read <R67> several times.
The only thing I would be changing is the pig-tail that connects the battery to the board, not the battery itself - which I’ve already told the team would be prohibited.
I’ll go back and re-post the question specifically asking about the pigtail and see what response I get. It seems to me that the Tamiya and Deans connectors are actually safer than the old box type.

BTW. I understand why they stay away from the LiPo’s. It would only take one team to leave it charging incorrectly for the evening and the whole venue could burn down by morning!

Thanks,
–Mark

7

Mark,
The answer would be the same if the battery should come loose and be crushed between two robots.