8 Batteries -or- 10 Batteries at Competition

[Michael Blake]

We now have 8 batteries and 8 chargers (6 amp max.)... from our rookie experience this season, this seems to be optimum for Regional competition all the way to finals matches...

IF we are fortunate to make it back to St. Louis, and REALLY fortunate/LUCKY to make it to Einstein... is 8 batteries with matching chargers enough or do we need 10 batteries/chargers?

How many batteries do the powerhouse teams use? 8? 10? 12?

THANKS for your help!

[Andrew Lawrence]

I don't know how many the elite teams have, but my mentor once told me, "You can never have enough batteries". Now, while that's a bit of an exaggeration, I suggest having around 8-10 with you. We usually have 1 on the robot, at least 3 at the ready, 1 in our robot cart, and at least 3 charging. Using this method, we've never run into a situation where we were lost on batteries. It's a good idea, though, to get around 80% of your batteries charged and at the ready near your final rounds, since you won't have enough time to go back to your pits and change them.

[AdamHeard]

At comps we have for matches we have 10 batteries, 10 chargers, and 10 dedicated slots. Battery A is always charged by charger A and so on.

We also bring 2-3 older batteries and mismatched chargers for programming, etc... When tuning autonomous or control loops we are forced to use match batteries, but we avoid using match batteries for trivial things when at comps. We also avoid using them for driver practice at home.

Good batteries versus poor batteries are a substantial performance and reliability difference.

[JesseK]

We use a cyle of 3 batteries during Quals, and haven't ever seen a [newer] battery take longer than 45 minutes to hit its peak charge. We have 2-3 in reserve for Elims that are used once Thurs/Fri (for 'difficult' matches) and then not again until Elims Saturday. Thus for Elims (6-9 matches max), we have 5-6 batteries available. We also use our oldest battery as a 'test' battery (autonomous, pre-match flight test, etc) and it stays on the robot cart. Unless we had an automated charging station, having more would be a nightmare for us.

For Einstein, you'd have 9 Elim matches (at most) in the span of 2 hours for Division Elims, and then 6 Elim matches (at most) after that. Einstein also has many long break in between the matches -- especially when Dean Kamen speaks. New batteries take ~30 minutes to [mostly] charge back up from the drain of a 2 minute match. So you may be able to shift your question to more of a "why are our batteries being drained so much during a single match?" type of perspective if you really feel you must have 8 batteries available for an event.

I'll add that year-over-year (now in our 7th year), we only have to purchase 2-3 new batteries because of our setup, and we've never come across a 'bad' battery in the bunch of batteries that are less than 4 years old. It works for us, though I admit we've never made it to Einstein.

Another tidbit is that you may want an extra battery or two for your alliance partners at some point. Yet again, we've never had an issue were we had less than 2 batteries that weren't at their prime during Elims, so 6 batteries still work for us. Maybe we haven't been around enough...

[AdamHeard]

So you may be able to shift your question to more of a "why are our batteries being drained so much during a single match?" type of perspective if you really feel you must have 8 batteries available for an event.

Some teams design systems that are very overpowered, but purposefully so, for a large performance benefit.

I know teams with high capacity and fast dumpers in 09 like us and 254 used some serious battery when scoring, but it was worth it for the speed of scoring.

Also, gearing for 17 fps or so in drive results in some real performance gains if the driver can handle it, but consequently you're using a lot more battery.

We're not draining a battery per match, we make sure of that much, but we're not getting 20 minutes out of a battery.

[JesseK]

Some teams design systems that are very overpowered, but purposefully so, for a large performance benefit.

I know teams with high capacity and fast dumpers in 09 like us and 254 used some serious battery when scoring, but it was worth it for the speed of scoring.

Also, gearing for 17 fps or so in drive results in some real performance gains if the driver can handle it, but consequently you're using a lot more battery.

We're not draining a battery per match, we make sure of that much, but we're not getting 20 minutes out of a battery.

Consider that elite powerhouses understand this up front, and use it as a tradeoff when making both design and pre-season purchase decisions. <Insert random young team here> usually doesn't understand that tradeoff during these types of decisions -- so it's important that you put the reasoning in with your explanation of "yes, we use 10 batteries". Otherwise, just like monkeys in a corporation, it's very easy for people [teams] to lose the understanding of why things work the way they do.

[Phalanx]

Somewhere between 9 & 12 batteries is what I recommend and what we as a Team typically use. As we've not yet made it to Einstein we work with 9 batteries as our regular rotation.

Our logic is as follows:
3 - Batteries for Divisional Quarter Finals
3 - Batteries for Divisional Semi Finals
3 - Batteries for Divisional Finals
---
9 - Batteries before you get to Einstein.

3 - Batteries for the Semi Finals on Einstein, as those 9 may or may not be fully recharged by the time the matches start.

12 - Batteries
---

Now, there should be enough time for the first 3 batteries used from Divisional SEMI's to be fully charged again and ready for the Finals on Einstein.

So I'd say no more than 12, but IMO, you'd probably be fine with 9.

[Peter Matteson]

We bring 6 batteries to the Championship every year. When eliminations come around we visit friends to get additional batteries, or get them from teams that are eliminated along the way.

[DaveCT]

We bring 6 batteries to the Championship every year. When eliminations come around we visit friends to get additional batteries, or get them from teams that are eliminated along the way.

This year we didn't end up needing to borrow any, we ran all of Championship with 6 batteries and 4 chargers. Requires paying attention to make sure 4 are always charging but nothing crazy. We actually had more minibot batteries than main batteries.

[JesseK]

Pre-match pneumatics charging also helps with match battery drain. Since we use a decent amount of pneumatic power every season in place of motors, maybe that's why we haven't found the need for more batteries per event yet.

Hmm.

[Aidan S.]

Our team brings 10 batteries to regional competitions along with six chargers. A battery used for only one match before it is re-charged. We have two battery chargers that re-charge batteries from one match worth of use in about 15 minutes, so we always have a good supply of charged batteries, and after the eliminations at both of our regionals we had about 3 fully charged batteries left (we played 6 elimination matches in Waterloo and 7 at GTR).

In St. Louis we brought eight batteries with us. Since there were long gaps of time in between each qualifying match, there was enough time to fully charge a used battery before our next match. We always had six fully charged batteries ready.

During the elimination rounds we cycled through all eight batteries in the eight matched we played, but we made sure to charge each used battery in case we made it to Einstein. By the time we were playing the third final match, we had six batteries ready for Einstein. Unfortunately we lost and did not make it to Einstein, but we were ready if we were needed as a back-up robot.

Ten batteries is more than enough for any FIRST event as long as the team effectively charges and cycles through all of the batteries. We used an identification system for the charged and uncharged batteries, so we always knew which ones had the most charge.

[Cory]

We purchase 10 new batteries every year. These batteries do not get used for anything other than competition matches.

If it costs $4,000-5,000 per event and you get eliminated because your battery was dead, the $390 it costs for 10 batteries looks like a pretty great deal.

We are also able to supply our elimination partner(s) with batteries when they do not have enough of their own.

[Hawiian Cadder]

we had 5 batteries this year, and I really wish that we had had 6 or 7. there was always one match each day that the robot didn't quite run at 100 percent.

[Chris is me]

If it costs $4,000-5,000 per event and you get eliminated because your battery was dead, the $390 it costs for 10 batteries looks like a pretty great deal.

Wow, that's certainly a compelling way to look at it. Never thought of a decision that way before.

[Enigma's puzzle]

We made a different investment. One of the mentors on the team made a load tester. We check every battery before it goes on the robot to avoid battery problems on field. But we only have 4 batteries. By being able to see the power that is given when a higher current draw is being applied we know exactly what each battery is going to give us every match.

With the load tester we are able to identify the bad batteries before we go to competition. When we first got the load tester 3 years ago (we were a third year team) we realized 4 of our 7 batteries were under performing and we no longer use them. Over the past couple years we have managed perfectly fine with 4 or 5 batteries with 3 chargers.

The MOST important thing we learned is load testing the batteries, instead of just testing with a voltmeter is essential to telling the true strength of a battery

[DonRotolo]

Two measures of battery performance: State of Charge (SoC) and Capacity.
Load testing measures capacity, and assume around 100% SoC
(Proper) voltmeter testing measures SoC, and will not detect a "bad" battery.

Anyway, to the original question:
We use around 10 batteries (plus 1 or 2 for testing, too weak for competition) with 6 chargers and one person in the pits dedicated to nothing but batteries. This gets us through qualifications and eliminations all the way through finals.

If we went to Einstein we would also be OK. In a pinch we could surely borrow a few charged batteries from an alliance partner or someone else at the competition.

Rather than some kind of calculation, we've found over the years that this is sufficient. Having more would be good, but not required. That's our experience so far.

Once a battery fails to load test normally, we retire & replace it.

[slijin]

I believe we bring 8 batteries & 6 chargers normally, but do keep in mind that however many batteries/chargers you need is contingent on how power-hungry your robot this year. Last year, we could run 2 matches on one battery in a row without any appreciable change in quality of performance, but this year, our battery was practically drained by the time we had to deploy.

Nonetheless, think about how many batteries you need going to competition, then bring 2-3 extra. It never hurts to be prepared.

[Michael Blake]

This is _great_ info... THANK YOU _all_ for your help!!