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Unread 07-02-2017, 17:07
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Re: pic: Power Over Ethernet for 2017

Quote:
Originally Posted by Mark McLeod View Post
I don't quite follow this logic.
My power injector uses three connections:
1) roborio RJ45
2) radio RJ45
3) direct wired into VRM after cutting the barrel connector off
I was assuming you were using the connector link attributed to you (https://www.amazon.com/iCreatin-Pass...416072&sr=8-19)
on both ends. Apparently I've misunderstood the planned implementation. But my comment of things being less reliable assumed you were plugging the dongle with the male barrel into the radio, along with the RJ45 end.
The other dongle plugged into the RIO, then a power extension plugged into the female barrel to get to a VRM. An Ethernet cable plugged in to bridge the gap between the two dongles. So to tally things up I was expecting 4 Ethernet connections and 2 power connections. Basically exactly the layout depicted in the last two images of the product page linked.

If you're only using one of the cables, cutting the barrel jack off one end, and plugging it into the VRM directly... then I would agree you have one fewer Ethernet connections in this implementation than what I was suggesting. As far as I can tell, nobody suggested this implementation before I posted.
In this configuration, you will need the VRM immediately next to the RIO unless you're going to solder extensions to the power leads (which per your comment - you apparently consider to be introducing a failure point). Personally I trust our teams ability to produce reliable solder joints, so I consider this a wash.

Quote:
Your solution appears to require one additional Ethernet cable adding RJ45 failure points over and above those others even after you've bypassed the power barrel connector (the user modification is also another potential failure point).
The component I suggest effectively turns two RJ45 connections and a barrel jack into 4 RJ45 connections with zero barrel jack connections. Personally I consider the RJ45 connections to be one of, if not the most, reliable connections on the robot. To prove a point, I've lifted up a kitbot chassis by an Ethernet cable, maintaining active comms. The objective for me in using POE is to remove the Barrel plug from the equation, as in my experience this is the only component which has contributed to comms problems on our robots. We usually hot glue them in... I've never had to hot glue an RJ45 cable into a socket.

I did consider using a cable like the ones you've linked. My concern with them was the quality of the crimps and whether or not the cables would be twisted pairs or (non-compliant) straight through in the dongle themselves. When I was doing my research at the beginning of the season, the pictures few pictures of the dongles I saw online looked to be questionably small gauge straight through conductors. I didn't have any of these on hand to check myself though. So I made a judgement call to go with the PCB version like the ones I linked earlier.

All that said, no need to defend your choices to me. I was just sharing what we were planning on doing since I hadn't seen a POE injector like the one we're using in this thread yet...
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