Answered: 9V backup battery

In the VEXnet upgrade documentation that we recieved, it says on the 2nd page: Optional for NON-COMPETITION use. Connect a 9V backup battery to the “backup” port of the VEXnet microcontroller upgrade module.

In both the Clean Sweep manual and inspection checklist, it says the 9V battery is required for competition use.

We didn’t notice this until now and do not have time to order a 9V backup battery holder kit (it did not come with the VEXnet?). If we don’t put in the 9V battery we run the risk of it resetting if the main battery goes out, but is it okay? Can we compete with out it if we’re willing to take the risk?

Hm…thinking about it.

Does optional for non-competition use mean

  1. Optional to use if you want or not…but for non-competitions only (you cannot use for competition)?
  2. Optional to use for non-competition but required for competition use?

…if it’s #2 why wouldn’t it be included in the VEXnet upgrade kit?

Some of the early releases of the VEXnet Microcontroller Upgrade may have gone out without the backup battery holder. All current releases do have it included. Please contact me directly with your information and shipping address and I will get one out to you as soon as possible.

The VEXnet Microcontroller Upgrade will function fine without a 9V backup battery attached. The backup battery’s function is to provide power to the Microcontroller processors and VEXnet Upgrade in the event of a loss of main power. This is mandatory for competition usage because we want everyone to have the BEST competition experience possible.

Some scenarios:

[LIST]
*]Your drivetrain becomes jammed up and your drive motors draw more power then the battery can deliver. As a result, the battery can’t supply enough power to the Microcontroller so it “browns out” and resets. When the Microcontroller resets it breaks the VEXnet link which must reinitialize. While this is occuring your robot is just sitting there. If you have the 9V backup battery on your robot, the Microcontroller never resets, and your robot continues to compete!
[/LIST]

[LIST]
*]One of the students on your team is bored and destructively decides it would be fun to shove a VEX open ended wrench into the connector of one of your batteries. He damages the pin inside the battery connector, but since the damage isn’t visible he puts the battery back in your competition pile. At competition this battery is used for a match, but has an intermittent connection. Your partner robot accidentally bumps into your robot, and jostles the battery. The battery connection breaks instantaneously which causes the Microcontroller to reset. Even though main-power was almost immediately restored, you still need to wait for the VEXnet link to reset. If you had a backup battery on your robot, none of this would be an issue. (Though, you should still probably get rid of the destructive kid on your team).
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In situations where a Microcontroller reset isn’t a big deal (non-competition) the backup battery isn’t important. When a reset can mean the difference between a match win and a match loss, you want to have the backup battery installed.