9 Volt Backup Battery (Is it Optional?)

During my state competition my robot stalled during autonomous which rendered our robot useless and we lost the match. We talked with the judges and were directed to the officials and they told us that the 9 volt was left plugged in when we turned off the cortex but caused the cortex to stay on when we reconnected to get ready for our match. I asked if we could remove it so it wouldn’t happen again and they told us that is illegal and would cause to be disqualified. The only purpose I’ve found with research about a 9 volt is that it provides a more secure connection between the cortex and controller. I was wondering can we get stop using a 9 volt or is it a mandatory part of the robot.

You will not pass inspection without it.

“Robot has a charged 9V Backup Battery connected”

Best thing to do is have a check list for pre-match and post-match. One thing on pre-match is plug in 9V. One thing in post-match is unplug 9V.

Thanks for mentioning about making a check list I will forward that to my team

Sure… They differ by season, and we didn’t do VRC this year, or I would give you ours. Maybe another team will see this and attach theirs.

Um… I don’t think I had a charged 9volt all year I just had a dead one on my bot. They never thought to check if it was charged

This is checked at Worlds. Completing this check would just be a waste of time at smaller events because of the comparative lack of manpower and low stakes.

All it does for my cortex it prevent it from turning off when I flip the switch to off after a match.

I understand it can also affect the Vexnet connectivity…

but doesn’t everything? lol

I think it is important to understand that the purpose of the backup 9V battery is not to power your robot mechanical functions, e.g., make the robot drive around and manipulate objects, but rather to maintain communications connectivity between the cortex and the VEXnet joystick controller when the main battery inadvertently disconnects, for example being bumped and loses power for a moment. If your 9V backup battery is not present, the cortex has to establish communications from scratch, which can be a long time in a match situation. The issue that arises is that the cortex is still powered by the 9V backup battery when the main power switch is off, so your initialization routines are not run.

The best practice is to come to the field with the 9v backup unplugged, robot and controller powered off. Then connect the joystick controller to the tower, then power on joystick and plug in 9v backup battery and power on robot. When done with match - turn everything off and unplug 9v backup battery and hit to pits.

Lots of steps. Check list good!

According to the table in <R14> there is not backup batteries for the V5 brain.

Yeah. It might have something to do with the fact that V5 doesn’t use a hobby style Tamyia connector, but rather a well engineered, purpose-built Molex.
And that the battery can sustain a very significant current (much higher that what the 8 legal V5 motors could ever pull at once) without much voltage sag.
(even with full 20 VexU-allowed motors working at the full power at the same time, the voltage likely won’t sag enough to cause a reboot, but at that point, you might be close to tripping the overcurrent limit in the battery…)

Well said. Even though it may be annoying to unplug the 9V, it is helpful. At our competition in Framingham, MA, our partner did not have a 9V. The field disconnected for a moment, and all robots resumed function after a second or two. However, @Brian_9605A could not reconnect for about 30 seconds due to his lack of backup battery

Actually, still not 100% sure what occurred in that case - he may have had the battery.

We work through a lot of gremlins - at Worlds we found that a battery extension cable was causing the power expander to drop out, and loss of functionality at very bizarre times. All crazy stuff we deal with. Debugging is a great skill to develop - life is not perfect.