Drone racing Power over ethernet, POE?

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ShowMaster
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Drone racing Power over ethernet, POE?

Post by ShowMaster » Fri Sep 29, 2017 3:51 pm

I’ve been asked to help with a drone racing wireless lap counting system.
The detection is wireless as they pass the gates, but the resulting data and power is via cabling. Cat5 for data and hopefully dc power for the 5ea gate sensor packages.
Each gate package will have a pie3, a nano, and 8ea 5.8g receivers.
The guess I’ve been given for required power, is 5v at 3A per gate package at up to 100ft of cat5 run for each of the 5.
Maybe 12vdc or higher and regulated to 5v at each pack?
Doing some searching and quick math, I’m not sure the cat5 can deliver the required current over a 100ft max distance, especially if we have 100f days?
Some will be shorter runs, all going to a single station collecting data, but 100ft seems to cover most max runs.

If anyone has dealt with Poe or racing setups, I could use some ideas.
Local batteries work I’m told, but can go dead at the wrong times if not closely monitored.
It would seem that one solution would be cat5 with a attached second set or larger wires for power only if it exists. A second run of cat5 or wire for power only could be added, but not being bonded to the cat5, it would require taping it every 6” to make it manageable. Tape gets sticky and dirty.
Being a portable system, buried cables aren’t an option.

I’m not even sure the RJ45 connector pins can handle that much current?
The Poe adapters are expensive and are also limited on current I’m reading.
No diy options I can find so far?

One other option would be Ethernet over coax?
The combo cable has 75 ohm coax and a molded in 2ea 18ga wire pair.
The drop of 18g at 12v 3A over 100ft is about 3.82v calculated. Using a boost regulator, the starting supplied voltage could be made 16vdc.
All the package electronics run on 5v or less, so the 12v is regulated to 5v.

Ideas welcome
Thanks







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Kilrah
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Re: Drone racing Power over ethernet, POE?

Post by Kilrah » Fri Sep 29, 2017 4:31 pm

A quick search for PoE specs suggests 600mA max per pair, and use of around 50V to get decent power given that limit.

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Re: Drone racing Power over ethernet, POE?

Post by ShowMaster » Fri Sep 29, 2017 4:46 pm

Yes, that’s what I’m finding.
Ethernet over coax with the 18ga accessory pair may be the all in one cable option.
Wishing and reality doesn’t always work out.
Using 5A lipo packs and changing them every hour of on time seems the best option.
Since a pie3 is managing data at each location, maybe added code to monitor and report back battery charge info would avoid unexpected brownouts.
I’m thinking how simple my fixed wing aircraft is to fly.
No fpv video channels to coordinate, no lap counting, just a lawn chair if it’s a lazy fly day.
I’ll gather all the remote power options I can and then they’ll have to accept them for now and move forward on building a working system to use.
They have open source info and the parts, power will be what it will be.
Thanks





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Carbo
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Re: Drone racing Power over ethernet, POE?

Post by Carbo » Fri Sep 29, 2017 5:21 pm

Ethernet 100 uses only 2 pairs, why not split the cable and use better connectors for power? The cable can handle 2x 0,57 A. Using two DC-DC converters you can send about 50W @ 50V. It´s an elegant solution in my pov.

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Re: Drone racing Power over ethernet, POE?

Post by ShowMaster » Fri Sep 29, 2017 9:15 pm

So using the 50w figure and 2 pairs broken out of the cable, feed with let’s say 50v, I could regulate it at the other end, down to 5v at 3A, 15w?
A buck regulator is 35v in max I’m looking at.



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Carbo
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Re: Drone racing Power over ethernet, POE?

Post by Carbo » Fri Sep 29, 2017 9:52 pm

With a 35V DC-DC you can transmit about 35W using the free pairs. If you need 15W, you will get about 0.5A. A 35V step-up module and a SBEC will work.

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ShowMaster
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Re: Drone racing Power over ethernet, POE?

Post by ShowMaster » Sat Sep 30, 2017 7:10 am

Is my math and thinking feasible?
If 2ea 24ga wires are paralleled, I think it makes a 21ga wire. Resistance for 100ft would be 1.28ohms
Doing this twice it would add up to 2.56 ohms.
7.68 voltage drop for 3A.
The pie3 and all the electronics wants 5v. So using a 3-5A buck boost regulator set for 5v out should work.
Then 35 or even 24v may work.
The real test is to just simulate the setup with 100ft of cat5 and draw 3A at 5v from the regulator, upping the supplied voltage until there’s some headroom for the regulator. Then calculate the wattage to not melt the cable. Under 50 watts?
Use pure copper cat5!

Your idea of breaking out the unused pairs from the RJ45 is a good one.
Inexpensive Poe.



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Carbo
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Re: Drone racing Power over ethernet, POE?

Post by Carbo » Sat Sep 30, 2017 8:04 am

Eventually the language barrier on my side is in the game, sorry for that.

You calculate the voltage drop with 3A, but there are only 0.5A, when you transfer the 15W with 35V (I=P/U), or 0.7A, when you transfer with 24V (some loss for transforming already taken into account). The voltage drop is only [email protected] (a loss of 3.7%) or [email protected] (a loss of 7.5%). Transfering the same power with higher voltage reduces the current and the loss. On the other side there is a loss in the two DC-DC converters, but they work with high effeciency >90%. Overall a clear advantage for the higher voltage - and in your case it is the only way, to stay inside the cable parameters.

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jhsa
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Re: Drone racing Power over ethernet, POE?

Post by jhsa » Sat Sep 30, 2017 10:15 am

This is what is normally done to transfer electricity over long distancies.. :)

João

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Re: Drone racing Power over ethernet, POE?

Post by ShowMaster » Sun Oct 01, 2017 7:52 am

Thanks. I’ll give it a try.


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Re: Drone racing Power over ethernet, POE?

Post by ShowMaster » Wed Oct 11, 2017 1:39 pm

I’m now told that the length could be 200ft for some of the gate runs from the computer station.
This will be interesting to deal with.


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