NXT Brick Low Battery Problem
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Author:  Jonathan [ Tue Sep 23, 2008 11:30 am ]
Post subject:  NXT Brick Low Battery Problem


My team got our FTC kit yesterday and I've been trying to program it with RobotC. However, when I connect the Motor and Servo Controllers to the NXT Brick (Sensor port 1, 10-Cell battery pack connected to controllers, one DC motor and one Servo connected to controllers) and turn the switch on, the Brick (with RobotC firmware) says low battery. The Brick has a fully-charged lithium battery pack, and the 10-cell NiMH battery pack is also fully charged. When I tried this same thing with NXT-G firmware on the Brick, I didn't get this problem.

Anyone know what's wrong?


#2945 Power Surge

Author:  Jeff McBride [ Tue Sep 23, 2008 11:52 am ]
Post subject:  Re: NXT Brick Low Battery Problem

We've seen the same problem. It appears to be intermitent. Sometimes hitting buttons on the NXT will make it go away. Sometimes you have to turn the NXT off and on. Eventually it works again.


Author:  tfriez [ Tue Sep 23, 2008 5:54 pm ]
Post subject:  Re: NXT Brick Low Battery Problem

Fixed in version 1.44.

FYI - Only the motor controller has a voltage reading... the servo controller cannot return the voltage of the battery.

Author:  Jeff McBride [ Tue Sep 23, 2008 8:03 pm ]
Post subject:  Re: NXT Brick Low Battery Problem

Right but this is a big popup warning on the NXT display itself. Is it complaining about the external battery or the rechargable NXT battery? Both are fully charged. If it is complaining about the external battery, it shouldn't complain if you only have an FTC Servo Controller installed.


Author:  mightor [ Wed Sep 24, 2008 7:30 am ]
Post subject:  Re: NXT Brick Low Battery Problem

I've noticed this warning if there was a short in my sensor board. I was using the HiTechnic Proto Board at the time.


Author:  CC335 [ Wed Sep 24, 2008 3:37 pm ]
Post subject:  Re: NXT Brick Low Battery Problem

I get the same problem when I run the sissors lift on my prototype FTC robot. Fresh batteries work well (or recharged batteries, if you use the battery pack)

Author:  Dick Swan [ Sat Sep 27, 2008 3:45 am ]
Post subject:  Re: NXT Brick Low Battery Problem

The original FTC / Tetrix prototype used 2 x 7.2V batteries and the external battery low voltage indicators were not changed until version 1.44 to reflect the single 12V battey that is shipping with the kit. This explains the frequent "low battery display" with the 1.43 release that shipped on the CD with the FTC kits.

In version 1.43 and earlier, the low battery pop up warned for both the internal battery and the external battery. For version 1.44, it was changed to occur only for the internal battery. Yes, it is desirable to also generate for external battery but I didn't have one yet to test so I disabled the check.

There is an easy way to adjust the sensitivity of the low battery popup. There's a couple of fields in the "System Parameters" debugger related to this that you can fine tune. I think you have to be in "Expert" Menu Level to get this particular debugger window.
  • the variable is "low voltage battery count limit" and represents the number of contiguous low voltage values that need to occur to trigger the popup display on the LCD. Try increasing this value and it may eliminate transients. I recall that a value of '0' will disable the popup display totally.
  • "muxLowBatteryShutdown" is a low voltage limit for the external battery used to disable the motors. It should be set to around 10000 which will display as 10.0 V. It looks like it currently reflects 12.0 V which is a value appropriate to the older 14.4 V battery level. This will be automatically changed in next release of ROBOTC (version 1.45). This check is designed to protect against excessive discharge of the battery which will dramatically shorten its life.I recommend everyone make this change.
Both of above values are stored in flash memory. So they only have to be set once per firmware download.

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