Better Battaries for Driver Pratice
 

This post is asking about robot battery alternatives for driver practice not for competition. When doing driver practice we will kill a battery in about 6-8 minutes maximum. We only have so many batteries and thus it limits the amount of time we can do driver practice. Does anyone know of an alternative way of powering a robot for longer? Possibly a battery that is not competition legal but will last longer for practice?

Re: Better Battaries for Driver Pratice
 

Buy more batteries. Not only do you get more drive practice, you get more at competition too!

8 batteries gets you 45 minutes of continuous practice time. Add in a bit of a break and then you can start practicing again. Plus you get to use one battery per match in eliminations, which is really nice.

Re: Better Battaries for Driver Pratice
 

It takes about 3 hours for us to charge a battery. Is that because we have bad chargers? Would plugging multiple chargers in to the same strip slow them down that much?

Re: Better Battaries for Driver Pratice
 

Okay, so "a bit" is a little longer than I remember... Still - consider upping to about 12 batteries. That will give you 90 minutes continuous, so about 2 hours of practice at a time, which is pretty dang good.

You want to practice with your competition batteries, so everything behaves as expected on the field.

Re: Better Battaries for Driver Pratice
 

Hi, I am the battery guy (aka Battman) for team 1676.
We have 10 good batteries and 6 chargers. Each battery is 18Ah. Each charger can charge at up to 6 amps. By basic math it takes a battery that is 1Ah (in capacity) that is being charged at 1 amp, 1 hour to charge. So our FIRST robot batteries will take 3 hours to charge because they are 18Ah and are being charged at 6 amps.

If we were to purchase chargers that could charge batteries at, lets say 8-10 amps (which would result in faster charge times). There is always the possibility that we could blow the batteries up. And if we didn't blow the batteries up we would wear out the batteries faster then if we charged them at a slower rate. Basically we would have to replace batteries every year rather than every 2-3 years. And that would cost teams a lot of money. As a set of 2 batteries from ANDYMARK are $83.00.

Also we could purchase non-competition legal batteries that were the same physical size or larger and use those during driver practice. But on the other hand you don't want to be driving around with a 40lb marine battery running your robot. you may get exceptional run-time but it will cut into the robot's performance. Batteries that are the same physical size but have a higher capacity would be ideal for use, but they would cost teams even more money, and could possibly run teams $100+ per battery.

Also there is another aspect to charging times. This applies to all batteries. As batteries become more charged they will start accepting less and less voltage. therefore it will take longer to charge. The first 75% of a battery charge will take approx. as long as the last 25%.

And finally the last factor in run-times is the heat that you generate. As you run your robot more and more electronics start to heat up naturally. But the parts that heat up the most are the connections from the battery terminals to the PDB. Also the motors Heat up quite nicely to the point that they will burn you. And finally if you have a compressor (we have had the past 2 years) your battery life will go out the drain (plus that heats up quite well too). Parts like the C-RIO and ESCs wont heat up as much for one of two reasons. 1) they have a fan or 2) they dont have as much power flowing through them.

I think i have covered all of the bases of run-time and charging time. Please let me know if you still have questions...

Re: Better Battaries for Driver Pratice
 

I'm not trying to put words into Chris Picone's post, but here's what I think he means. Suppose you got a 12v marine deep discharge battery and hitched up an Anderson connector to its terminals. It might then power your robot for a significantly longer time than the regulation batteries. However, the increased size and weight of that battery would significantly change the driving characteristics of your robot by traction, turning momentum, geometry of gripper arm's motion due to its size and alternate placement, etc.

The consensus seems to be invest in more of the same batteries and practice with them. You'll also get practice changing the batteries on the robot so you'll realize how important easy access is to the power source. To this I'll add: look around CD and other places for ideas about how to make a combination battery cart and charging station. Ride herd on your energy sources. It's also interesting to note that many teams have named their batteries for easier and more effective handling. It's much better to say "I'm going to use Delta now." than to wonder if an anonymous battery has a proper charge.

Re: Better Battaries for Driver Pratice
 

Chris, since FRC batteries never get down to 0v during competition (or practice), there's always some charge left on it, so it shouldn't take 3 hours to charge a battery that was normally used.

Re: Better Battaries for Driver Pratice
 

Batteries don't need to go down to 0v to be empty. Also by the same logic a half full 12v battery doesn't put out 6v. This isn't for the batteries we use but look at this chart for a conceptual example http://joe.lagrecafamily.com/wp-cont...voltchart1.gif .

Re: Better Battaries for Driver Pratice
 

Hi. Ben Sherman,
i know that batteries never go down to 0V. but they still take 3 hours to charge. if you had read my whole post you would have seen that i said "the first 75% of a battery's charge will take just as long as the last 25%, as it starts accepting less and less voltage."
Because of the characteristics of the battery it will take the 3 hours to charge.

Ask Mr. Don Rotolo if you dont believe me. I got my information from him.

Re: Better Battaries for Driver Pratice
 

Just to clarify: 18Ah is a measure of the energy stored in the battery, not the energy required to charge it. The charging process is not 100% efficient.

Re: Better Battaries for Driver Pratice
 

That's true, chris. I believe it's called the absorption/float charging (I'm not sure of the name)

Re: Better Battaries for Driver Pratice
 

You might try scheduling more practice sessions, and have them be of shorter duration. I don't know how many hours a day you practice, but it must be more than an hour at a time if you're not able to get it done with 10 batteries that each last 6 minutes.

If you have to spend more than an hour practicing, then you might try using the batteries when they're only about 75% charged, and limit them to 4 minutes of operation.

Or schedule a five minute cooling off period after each five minutes of driving.

Re: Better Battaries for Driver Pratice
 

Get a new charger...Ours do not take 3 hours to charge ... usually close to 20-30 minutes. Our charger can charge a battery at up to 15 but we usually charge them at 10 or 5. It can also choose what to charge it at, somtimes it chargers at 0.2, but this takes FOREVER to charge them fully.

http://www.canadiantire.ca/AST/brows....jsp?locale=en

Here is the link to our new chargers ^^ ... i dont think america has Canadian Tire though :$

Re: Better Battaries for Driver Pratice
 

Thank you. I forgot to state that "Ah" (amp hour) is a measure of capacity.

And Ben Sherman. The type of charging we use is called absorption. Most laptops and mobile devices will use this type of charging as well.
Float charging is more commonly known as trickle charging. It is used on High Performance NICD, NIMH, LIPO, and A123 batteries to keep them from self discharging. This method doesn't hurt or damage the battery. where as if you did that with a lead-acid battery it would start to damage it after a while.

The reason that you can charge your batteries so quickly is because you have the ability to charge at 2A, 10A, and 15A. When you charge a battery at 15A, it may charge really quickly but it also increases the chance of blowing up your batteries. Plus they are not competition legal. but for driver practice they are probally great.

Re: Better Battaries for Driver Pratice
 

We always have a minimum of ten "good" batteries on hand -- it's something I got caught off-guard with as a rookie mentor in 2001, and not something I intend to ever do again.

Budget for extra batteries and chargers, and build a battery charging cart. Number or name all of your batteries, and include them on your pit checklist between matches. (Keeping track of the voltage going on and voltage coming off each match can help keep you ahead of cells that are dying for one reason or another, in addition to keeping your 'bot from dying in the middle of a match.)

Re: Better Battaries for Driver Pratice
 

Float charging and trickle charging are not the same thing.

You can leave a lead-acid battery on a float charger.

Re: Better Battaries for Driver Pratice
 

There are deep discharge gell cell batteries in the typical lawn tractor size that will give allot more power for a little larger case. Long run times can be dangerous with thermal issues. Sears sells a wheel chair battery that is not bad. I use the same case size but much more power battery for my power lift equipment. I'm paying 160$ for the good ones.

Re: Better Battaries for Driver Pratice
 

Oh wow. I never knew that there was a difference between the two. The difference is very minimal.
So basically a float charger is the "smart" version of a "dumb" trickle charger. Cool.

Re: Better Battaries for Driver Pratice
 

akoscielski3, how many batteries have you blown? While charging them at 15A may increase the risk of blowing them out if you haven't blown any it's probably a negligible risk. Getting new chargers is so far my favorite solution.

True, however while we can work around the problem I'd rather find a fix.

The only reason I would hesitate to do that is the first 2-3 minutes of battery life are noticeably the best. The robot moves faster and it's closer to competition settings (2.25 minutes of a fresh battery). I don't like loosing that cream of the crop battery time but it's better then nothing.

Re: Better Battaries for Driver Pratice
 

Taking 3 hours to recharge a battery seems way too long. Also, what voltage are you running your batteries down to?

We practice 5 days a week for an average of 4 hours a day. When we practice we try to never let the battery drop below 12.0V at idle. This is usually 1-3 matches depending on the robot and how much power draw their is during a match. By the time we've gone through all 6 batteries, the first battery is ready to go again. We've also found that by doing this we can actually recondition the battery and keep all of the batteries between 12.8 and 13.1V at idle.

Re: Better Battaries for Driver Pratice
 

Depends on the perspective I guess. To a lead-acid battery it's not minimal, it can be the difference between life and death.

Re: Better Battaries for Driver Pratice
 

A lot of the damage to these batteries comes from charging them at high temperature. More current makes a battery hotter. If you're force-feeding a FRC-legal battery with 15 amps for more than a few seconds, you're abusing it. It'll most likely treat you badly in return.

Re: Better Battaries for Driver Pratice
 

We have never blown a battery. I dont believe that we have charged on 15A before. :P

Re: Better Batteries for Driver Practice
 

He's a liar, I wouldn't believe a word he says!
The batteries remain competition-legal regardless of the charge rate. The chargers are not competition-legal, and are bad for the batteries (see Alan Anderson's comment above)

OK, so the problem is that the batteries are going dead.

The solution is the same as with my laptop computer: When the battery's dead, I plug it in and run off the wall outlet. (Translation: Find a 100A 12 V power supply and run heavy cables to the robot during practice). :p

(Oh, and Max: Battaries? Sheesh!)

Re: Better Battaries for Driver Pratice
 

There is another thread on this elsewhere, but the MFRs recommended maximum charger rate is a little under 6 amps for these batteries. You can do higher at your own peril.

Re: Better Batteries for Driver Practice
 

How are the chargers not competition legal ??

Re: Better Battaries for Driver Pratice
 

you might want to reduce your driving time a bit to allow all of the motors to cool and be sure you don't damage anything. Depending on which motors you are using and what kind of loads they are seeing, you may be generating a lot of heat.

we are using window motors for our lift arm, and even with a gas assist on the lift we limit ourselves to about 8 - 10 minutes of practice time before letting everything cool.

Re: Better Batteries for Driver Practice
 

I do not want to be near a battery that is being over-charged, and I am glad they do not allow this unsafe practice at competition.

Re: Better Battaries for Driver Pratice
 

haha. I keep telling everyone on our drive team and anyone who is with us that we need to allow the motors and other electronics to cool. But unsurprisingly no one listens. When we did our driver practice last Saturday, after about 6 batteries i smelled something weird. it almost smelled like burning electronics. But there was no magic smoke. so i went to feel the motors to see how warm they were, and almost burned my fingers. i told everyone that we needed a 15 min break to let everything cool. (which we did) After the break i could see a noticeable increase in performance.
Also we run super shifters with 2 Cims. We drive our robot around in high gear and when we hit the shift button we shift into the lower gear for more precise maneuvering.

If anyone with a good amount of knowledge in electric R/C's knows that when you start heating up your motor(s) they will degrade in performance. Also high mAh batteries will start to heat up they will start provide less voltage and your truck/car will start to go (slightly) slower.

Re: Better Battaries for Driver Pratice
 

OK,
Let's get some info straight here and in one place.
1. Our batteries are specified by the manufacturer to be charged at 6 amps or less. Battery life can be significantly increased when charged at 1/10 C or about 2 amps.
2. Life is significantly reduced by heavy loads like an FRC robot drawing currents in excess of 200 amps over a two minute match.
3. Charging at high current on our batteries causes internal heating and the possibility of out-gassing and case failure if the vents do not operate.
4. Our batteries are AGM types and the plates within the cells are not as robust as older technology lead-acid batteries.
5. Excessive heat within the battery causes the plates to deform, leading to internal shorts and a variety of other issues leading to lower battery life.
6. Hot batteries during charge can fool many/most smart chargers into producing damaging voltage/current during the charge cycle.
7. AGM batteries are nothing like NiMH, NiCd, LiPO, Li ION or other types and each requires a specific type of charger. Do not mix chargers and battery types.

Now on to the problem...
You can use a larger battery, the marine type for example. It must be a 12 volt battery of course. The motor heating encountered should be relatively the same with any size battery you choose. If you are interested more in practice then in demo, I would suggest that you stick with the FRC robot batteries for a variety of reasons. One is that the larger battery will be much heavier and while practicing, you will be over compensating for the added weight. Also, the larger battery will be able to better supply current to your motors giving you performance that will not exist in competition. If your robot draws a lot of current then the larger battery will also lure you into a false confidence that the battery will continue to supply enough voltage to prevent the systems from shutting down. Remember that the Crio monitors the battery voltage and inhibits all output when the battery falls below 5.5 volts at terminal voltage. The regulated supplies in the PD fail at about 4.5 volts which cause both Crio and radio reboots. If you want real world practice you need to keep real world conditions.

Re: Better Batteries for Driver Practice
 

In prior years, there was a rule that would have fallen between <R34> and <R35> in section 4 of the 2011 game manual. Here is 2009's <R39>:
The rule was not present this year. Even without a rule specifying so, it's still wise to use automatic chargers that don't exceed 6 amps.

Re: Better Battaries for Driver Pratice
 

Thanks for the clarification. Now I know. Although our team does NOT charge them at 15 or 10 amps, so we should not have a problem with any of this :)