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Unread 02-06-2017, 05:59 PM
Rob Heslin Rob Heslin is offline
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pic: Power Over Ethernet for 2017

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Unread 02-06-2017, 06:00 PM
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Re: pic: Power Over Ethernet for 2017

Thank you for this resource. At out meeting tomorrow, one of the things on the agenda is tackling POE. This should make the process much quicker.
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Unread 02-06-2017, 07:45 PM
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Re: pic: Power Over Ethernet for 2017

Thanks for this, but a few questions.

1. Will any inspectors not understand this and fail it because they have never seen it? I know that impossible for people to answer but whats your opinion.

2. How reliable is this for vibration? I know last year was a tough game for robots and many people has the radio power fail them, but is this any better? If seems like it would be but do people know for sure?

3. I assume you have to make up your own custom cable by using an RJ-45 end and then just running the conductors where they need to go?

Thanks
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Unread 02-06-2017, 07:54 PM
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Re: pic: Power Over Ethernet for 2017

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Originally Posted by amesmich View Post
Thanks for this, but a few questions.

1. Will any inspectors not understand this and fail it because they have never seen it? I know that impossible for people to answer but whats your opinion.

2. How reliable is this for vibration? I know last year was a tough game for robots and many people has the radio power fail them, but is this any better? If seems like it would be but do people know for sure?

3. I assume you have to make up your own custom cable by using an RJ-45 end and then just running the conductors where they need to go?

Thanks
1. Definitely bring along a diagram with you to explain to your inspectors what this is.

2. I didn't have experience with it personally, but I heard lots of anecdotal evidence that this was the go-to solution for vibration-related radio power issues for many teams last season.

3. Yup. It's essentially making a custom/more compact version of one of these cables: https://www.adafruit.com/product/435. There are several available on Amazon as well, if you want to avoid making your own cable.
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Unread 02-06-2017, 08:19 PM
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Re: pic: Power Over Ethernet for 2017

We used the Adafruit cable last year and liked it a lot. It's also nice because you can use the POE and barrel jack together and have some redundancy.
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Unread 02-06-2017, 08:52 PM
Rob Heslin Rob Heslin is offline
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Re: pic: Power Over Ethernet for 2017

Also Mark McLoud posted, in another thread, this cable:

https://www.amazon.com/iCreatin-Pass...416072&sr=8-19

It looks like the adafruit ones. Didn't see it when I posted the picture. Also here is a Q&A saying this sort of thing is legal:

https://frc-qa.firstinspires.org/qa/242

Your inspector's understanding of it will vary.
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Unread 02-07-2017, 09:37 AM
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Re: pic: Power Over Ethernet for 2017

Awesome ! Thanks.
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Unread 02-07-2017, 09:58 AM
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Re: pic: Power Over Ethernet for 2017

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Originally Posted by AllenGregoryIV View Post
We used the Adafruit cable last year and liked it a lot. It's also nice because you can use the POE and barrel jack together and have some redundancy.
I'm assuming you mean run a separate cable for the barrel jack and not trying to plug in both the Ethernet pigtail and the barrel jack from one of the Adafruit cables into the radio right?

Just so it's clear to others, that would not result in powering the "PoE" port on the radio as the Ethernet pigtails on those cables do not have power on the pins, the Ethernet cable you connect to the female Ethernet jack on the cable does.
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Unread 02-07-2017, 10:00 AM
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We are planning on using a passive injector similar to these: https://smile.amazon.com/gp/aw/d/B00...ds=passive+poe

We will be removing the barrel plug and soldering in a whip that can plug directly into the VRM.

Note passive poe injectors are explicitly allowed per the blue box of R51. So as long as you can explain I would find it hard to fail inspection.

The advantage of using something like the one I linked is the reduction of single point failures. There's only one cable plugging into the radio (not an Ethernet cable AND a barrel plug). This is at a cost of a single additional RJ45 connection and the loss of a barrel jack connection (which is the one that usually fails you since there is no positive retention. With the previously linked cables, you're reducing the wires that need to run across the robot, but you have increased the number of failure points as there are two additional RJ45 plugs and one additional barrel jack connection. So reliability has actually gone down.
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Unread 02-07-2017, 10:06 AM
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Re: pic: Power Over Ethernet for 2017

Quote:
Originally Posted by RufflesRidge View Post
I'm assuming you mean run a separate cable for the barrel jack and not trying to plug in both the Ethernet pigtail and the barrel jack from one of the Adafruit cables into the radio right?

Just so it's clear to others, that would not result in powering the "PoE" port on the radio as the Ethernet pigtails on those cables do not have power on the pins, the Ethernet cable you connect to the female Ethernet jack on the cable does.
I think the idea is to take the power for the Radio and split it with something like this:
https://www.amazon.com/SIM-NAT-Split...dp/B01GPRLQCC/

You then plug one of the male plugs directly into the radio, and the second male plug into:
https://www.amazon.com/iCreatin-Pass.../dp/B00NRHNPUA

The male Ethernet connector goes into the RoboRio, and you use a CAT5 or CAT6 cable to connect the female end into the radio.

Thus, the radio receives power directly, and through the Ethernet cable.
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Unread 02-07-2017, 10:11 AM
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Re: pic: Power Over Ethernet for 2017

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Originally Posted by otherguy View Post
We are planning on using a passive injector similar to these: https://smile.amazon.com/gp/aw/d/B00S5ROQO6
Interesting. I think I like the pigtail option better because we can use electrical tape to keep the plug from coming apart.
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Unread 02-07-2017, 10:14 AM
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Re: pic: Power Over Ethernet for 2017

FYI, this was covered in LRI training as well. So as long as you really are using a passive injector, your worst case scenario is having to escalate to the LRI.
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Unread 02-07-2017, 11:24 AM
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Re: pic: Power Over Ethernet for 2017

Quote:
Originally Posted by RufflesRidge View Post
I'm assuming you mean run a separate cable for the barrel jack and not trying to plug in both the Ethernet pigtail and the barrel jack from one of the Adafruit cables into the radio right?

Just so it's clear to others, that would not result in powering the "PoE" port on the radio as the Ethernet pigtails on those cables do not have power on the pins, the Ethernet cable you connect to the female Ethernet jack on the cable does.
Yes I mean running a separate power cable for the barrel jack, and they are both powered off the VRM. You will know you did it correctly when you can unplug the barrel jack or the Ethernet cable and the radio still maintains power as long as one of them is still connected.
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Unread 02-07-2017, 11:58 AM
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Re: pic: Power Over Ethernet for 2017

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Originally Posted by otherguy View Post
With the previously linked cables, you're reducing the wires that need to run across the robot, but you have increased the number of failure points as there are two additional RJ45 plugs and one additional barrel jack connection. So reliability has actually gone down.
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

And an additional Ethernet cable is required from the passive POE injector to the radio.
So, four connections altogether.

Rob's solution has three total connections (and a few more user modifications).

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).
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Unread 02-07-2017, 12:22 PM
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Re: pic: Power Over Ethernet for 2017

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but you have increased the number of failure points ......... So reliability has actually gone down.
While the number of potential failure points has increased, the likelihood of a failure of any one of those points has decreased. Hence, the overall reliability has increased.

In our solution, we are powering both ways. So the risk of failure of the original path is unchanged, but now there is a second path that has to independently fail.
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