paper: Power over ethernet

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Power over ethernet
by: Skier492

This describes how we implemented power over Ethernet on our 2016 robot.

There has been much discussion on communication loss due to radio problems. The new radio, OM5P-AN, can use Power Over Ethernet (POE). This is allowed per rule R43 of the 2016 Game Manual. Using a positive engaging RJ45 connector is a distinct advantage over the friction engaging barrel connector.

To accomplish this, the same 12V -2A radio power from the VRM is connected to the 18-24V POE port (not the 802.3af POE port) using a modified cable (see attached). This leaves the 802.3af POE to connect to the RoboRio.

The Passive PoE implementation for Open Mesh devices consists of a Passive PoE feed with pins 4,5 as +12V and 7,8 as ground. The pin connection for the radio was found on the power injector page:
Like many passive POE implementations, this application is consistent with 802.3af mode B for the pinout configuration (but not voltage). Unlike Mode A that shares the data and power on the same conductors, Mode B makes use of the spare conductor pairs.

It is important that the POE power injection cable is not plugged directly into a non-POE device (such as the RoboRio).

Using this setup, we have experienced no loss of communication due to radio issues this year. We even had 2 (unintentional) tests of extreme brownout conditions that caused to RoboRio to reboot but the radio link was maintained.

POE_RR3015_FRC2016.pdf (8.65 KB)