Dump Backup Battery
 

Does anyknow if its against the rules to replace the backup battery with a 7.2v powersupply? We want to dump the backup battery and run everything off our 12v battery.

Re: Dump Backup Battery
 

Last year's rule - but don't expect it to change.

Re: Dump Backup Battery
 

Trust me, there is a reason for the backup battery. I don't want to go into why FIRST introduced it. While the robot can run without it, no servos will work without it. Don't try running off just the 12V battery.

Re: Dump Backup Battery
 

I believe, in addition to what Eric said, the backup battery is also to make sure the controller has enough power at all times (so it doesn't reset or loose contact with the OI if the 12v battery voltage drops).

Re: Dump Backup Battery
 

That's part of what I don't want to go into...'Nuff said.

Re: Dump Backup Battery
 

Originally Posted by Jack Jones

<R62> The 7.2V Robot Control backup battery must be connected to the Controller as described in the
Controller’s manual (the 7.2v battery should be charged to at least 7.0v before entering a match). As a
replacement for the FIRST supplied battery, any other 7.2V NiCad battery pack may be used.

And, athough the rule clearly says that "any 7.2 volt NiCad battery may
be used" the technical inspectors refused our use of a larger 7.2 volt
battery in a prior year. If you come to a regional with a different battery
you should make sure that you also bring the FIRST provided one just
in case...

Re: Dump Backup Battery
 

Or as all teams should, make sure you have a copy of the rule book with you during inspection (and at at all times).

Re: Dump Backup Battery
 

Gene,
I would have challenged that ruling. The training was pretty clear that any 7.2 volt battery was OK. The 7.2 volt battery insures that the RC proccessors stay active during 12 volt brownouts. The battery also feeds the radio modem and any servoes connected to the RC. IFI monitors your robot as you set up on the field and can tell the level of both batteries. If your 7.2 volt is missing or low they will alert you to replace the battery. Robots that have large current draw from the main battery will regularly pull that voltage down below the critical 7-8 volts needed to keep the RC alive so IFI came up with this change. You lose control of the robot for a brief time but you don't have to wait for reboot and initialization. Your partners thank you for having a charged and seperate 7.2 volt source for the RC.

Re: Dump Backup Battery
 

One other device that gets it's power from the "backup battery" that hasn't been mentioned in this thread is the CMUcam2. With the extra focus being placed on this device in CD right now, it would be good to remember that as well. I don't know for certain that we will be using this camera this year, but my guess is we will.

As far as using the 12v battery to drive a 7.2v supply as a means of eliminating the backup battery, forget about it. The only way to do this and still get 7.2v out of it even when the main battery drops below 7.2v would require a circuit with weight and size that exceeds that of the backup battery it's self.

Re: Dump Backup Battery
 

Huh? What is preventing you from doing it with an IC based buck/boost converter? Small surface mount IC plus an inductor and a few resistors is all I could see that would be necessary. I'm certinally no expert on power electronics, but I don't see what you would need that would be "a circuit with the weight and size that exceeds that of the backup battery".

Not that I would say its worth doing it, stick with the backup battery. If you are really worried about size/weight, there are plenty of suppliers of smaller premade 7.2V battery packs.

Re: Dump Backup Battery
 

Pardon me for asking but what do you think the advantage of using a 7.2v power supply would have been?

Based on the 5vdc Siemens inverters I use it seems like you just adding weight and volume to your bot. Am I missing something?

Pete

Re: Dump Backup Battery
 

we actually had our main battery terminal ripped off and we took off the back up battery and ran the 12v battery off the back up battery terminal it worked fine for us until we swapped out the ifi.

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Many are missing the point that the keyword here is backup. Any electronics added to replace the NiCad and yet store enough juice to power the RC (ETC.) during brownouts is sure to be less efficient than the NiCad.

That is, you can't get something for nothing! Instead of having a pre-charged NiCad, you use power from the main battery, which is a net loss of power available at the start of the match. You'd also gain weight!

Re: Dump Backup Battery
 

Again, the only advantage I could imagine would be gained by elliminating it would be a reduction of size and/or weight. I don't think it is possible to achieve both requirements based on what you are describing. (I don't mind being prooved wrong, it wouldn't be the first time.) The trick would be to have it supply enought power to keep alive all the devices that may be drawing from it when the input voltage drops to say 5vdc.

Now your talking. Just make certain it has the capacity to power all the devices that run off the battery.

Re: Dump Backup Battery
 

We can't really answer this for a particulr robot but let us remember that there are robots (many robots) that have inefficient designs that do run the main battery down to nothing in a single match. I have had teams that were actually proud of the fact that they killed a battery every match. With that being said, a power convertor fed from the main battery is still going to fail when a current demand on the main battery causes it to go to a couple of volts during a shoving match. Even with boost buck convertors, a 10 volt swing on input will not reliably keep the backup power up at 7.2 volts. In this case, two voltage sources are the best solution.