Hey Jude,
Be aware that alkaline batteries, which are the most common type of AA
battery, may not be the best to use for your robot. The reason is that the
six alkaline batteries when fully charged will have a voltage of 9.6 Volts.
As you're using the robot and the batteries discharge, the voltage will
decrease fairly rapidly; even when the battery has a fair amount of capacity
left the voltage can droop significantly. The more they are discharged the
lower the voltage gets. Lithium batteries tend to hold their voltage more
stable as the batteries discharge. The Lithium batteries that are made for
the NXT brick will be 8.4 volts when fully charged. Comparing performance
over the same amount of time, the voltage of the Lithium battery will stay
stable while the alkaline voltage is drooping substantially.
What does this mean to your robot performance? If you're using alkaline
batteries, the motors will move faster than the Lithium when both are fully
charged. So, alkaline batteries can give your robot more power / speed when
they are fresh. However as the alkaline batteries discharge a bit the motor
performance will slow down. This will possibly lead to inconsistency in
running your missions. If the kids refined their missions when the voltage
was low, the robot may perform completely differently when a new set of
batteries is inserted.
My team uses the Lego lithium battery pack. The kids on my team
periodically check the battery voltage as they are developing missions,
especially if they start seeing their missions failing. Use the NXT window
to view this while the brick is connected to the computer if using NXT_G.
Our team swaps the Lithium battery with a freshly charged one if the voltage
drops to about 8.1 Volts.
All that being said, besides Alkaline there are other types of AA batteries
being sold (including even lithium batteries which are pretty expensive).
Each battery type will have different discharge characteristics.
Andy
_____
From: First Lego League in Virginia and DC
[mailto:[log in to unmask]] On Behalf Of Jude Arulpragasam
Sent: Wednesday, October 20, 2010 9:48 AM
To: [log in to unmask]
Subject: Re: [VADCFLL-L] NXT batery warning
I would like to know if there is any advantage using re-chargeable battery
pack over individual AA batteries'?
I just bought new re-chargeable DC battery pack (NXT
<http://www.legoeducation.us/store/detail.aspx?CategoryID=178&by=9&ID=1971&c
=1&t=0&l=0> Rechargeable DC Battery
<http://www.legoeducation.us/store/detail.aspx?CategoryID=178&by=9&ID=1971&c
=1&t=0&l=0> (W979693) from Lego website.
Please give me some pros and cons on this
Thanks
Jude
_____
Date: Tue, 19 Oct 2010 20:36:44 -0700
From: [log in to unmask]
Subject: Re: [VADCFLL-L] NXT batery warning
To: [log in to unmask]
Our team started using AA batteries instead of the rechargeable battery
pack. But when they had to change the batteries, they had dismantle the
robot to get to the battery compartment. I am worried that the kids will not
put back the robot perfectly, if they have to do this just before the
tournament to have fresh batteries in. Is that how it is normally done?
thanks
Gaja
_____
From: Jerry Lorengo <[log in to unmask]>
To: [log in to unmask]
Sent: Fri, October 8, 2010 3:28:54 PM
Subject: Re: [VADCFLL-L] NXT batery warning
Agreed - always use fresh AAs.
The recharchable batter has a goofy memory and the voltage drop will make
reproducibility for missions almost impossible.
Sent from my iPhone
On Oct 8, 2010, at 12:48 PM, Lloyd O'Hara <[log in to unmask]> wrote:
We only use batteries and always make sure we have plenty on hand.
Also, I'm sure why you would take 2 sets of four AA batteries, the nxt takes
six AA..
Lloyd
----- Original Message -----
From: Viquar Shaikh
To: [log in to unmask]
Sent: Friday, October 08, 2010 10:50 AM
Subject: Re: [VADCFLL-L] NXT batery warning
To add to this --- no matter what - we always carry 2 sets of four AA
batteries - one is a new packed set. This is a good backup for these
'just-in-case' scenarios.
Thanks
Viquar
On Fri, Oct 8, 2010 at 10:32 AM, Brandy bergenstock <[log in to unmask]>
wrote:
This came across the Ga FLL yahoo group adn I thought it was important for
everyone to realize:
The other day my team had taken one of their NXT bricks with them to a
meeting. When we got home, the battery was completely discharged. After
recharging it, my daughter discovered that the "Sleep" setting was at 60
minutes. The brick had accidentally turned on during transport and since
the sleep setting was so long, it ran the battery down. We discovered that
the 60 minute setting is the default for both the 1.26 and 1.31 firmware
update. That is WAY too long!
If you have updated your firmware, you should check the sleep setting and
change it is a more reasonable time (perhaps in the 2-5 minute time frame).
This way you won't accidentally run down your battery. I'd hate for someone
to discover their battery was dead when they arrived at a competition.
To access the sleep setting on the NXT brick, go to:
Settings
Sleep
and then change the time with the arrow buttons
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