Reasoning for R44

[CrazyRussian96]

The wireless bridge power feed must be supplied by the 12VDC-to-5VDC converter (P/N: CLL25-24S05) connected to the marked 12VDC supply terminals at the end of the PD Board (i.e. the terminals located between the indicator LEDs, and not the main WAGO connectors along the sides of the PD Board) shown in Figure 4?8. No other electrical load may be connected to these terminals.
What exactly is the reasoning for the first part of rule R44 in the Game Manual? My intuition tells me that it is to prevent the D-Link from experiencing power loss due to an accidentally tripped breaker, which would cause the robot to become out of control. No amount of searching on the internet (and Chief Delphi) has yet found me a concrete answer beyond "Do this because the rule says so". Can anyone please confirm/disprove/elaborate on my idea?

[Andrew Schreiber]

Conjecture - The 12v output is regulated as opposed to the regular outputs which are simply output from the battery. You could check this by looking at the design of the PD board.

[Ken Streeter]

The wireless bridge power feed must be supplied by the 12VDC-to-5VDC converter (P/N: CLL25-24S05) connected to the marked 12VDC supply terminals at the end of the PD Board (i.e. the terminals located between the indicator LEDs, and not the main WAGO connectors along the sides of the PD Board) shown in Figure 4?8. No other electrical load may be connected to these terminals.

What exactly is the reasoning for the first part of rule R44 in the Game Manual?

The special 12VDC supply on the Power Distribution Board is a "boost" supply, which will supply 12V even when the battery voltage falls way below 12V. For more information, see the PDB spec sheet at http://www.usfirst.org/sites/default/files/uploadedFiles/Robotics_Programs/FRC/Game_and_Season__Info/2012_Assets/Power%20Distribution%20Board.pdf

From looking at the specs, it appears that 11V will be guaranteed from the "boost" supply even if the PDB input voltage (the battery) falls all the way down to 4.5V.

The boost supply is important for the wireless bridge, because it prevents the wireless bridge from rebooting (which takes about a minute) every time the robot suddenly draws a huge rush of current (say due to a pushing match) which could temporarily drop the voltage to well below 12V.

[FrankJ]

Exactly what Ken said. Anywhere else you get a momentary voltage drop. Bridge reboots. Comms drop. Robot stops. :eek: It was one of the issues documented in the Einstein report last year.

[CrazyRussian96]

Thanks for all of the responses!

[Doc Wu]

Although I understand that reasoning, does not the DC-DC converter do the same thing? When the input voltage drops, at what point does it's 5v output shut down at? Since it converts to 5v, even if it doesn't operate as a boost-buck module, it ought to be good to 6v in.

In addition, the D-link routers internal regulators work just fine at 12v and do their own internal conversion to 5v or whatever they use internally. We run them routinely on an old robot that was wired for the old Linksys bridge. (Discovered by accident, when a student didn't realize they weren't direct plug-in replacement)

It seems like all these voltage conversions are inefficient and redundant.

If your battery is dropping below 6v then you're probably only seconds away from it dropping below 4.5v anyway. Continuing to run like that only damages batteries.

Note that this is just a theoretical discussion. If your robot is not wired to the current rule, I'll still call you out on it in inspection!

[EricVanWyk]

If your battery is dropping below 6v then you're probably only seconds away from it dropping below 4.5v anyway. Continuing to run like that only damages batteries.

The power supplies are staged such that motor power is intentionally cut a volt or so before the brains and radios cut. This helps prevent death during pushing matches, but doesn't replace having fully charged batteries.