Tether system

Wardhan · Jul 24, 2017

I am starting to work on a small project - trying to build a tether system for P2V+ (currently). The controls will be using joystick and laptop (or any OS based system). I am trying to figure out what I would need.

I want to remove the wifi unit, RC transmitter and receiver completely. Instead the power should be supplied from a deep cycle car battery (12v) along with entire controls of the bird. Dont need compass, GPS locking as the bird just needs to fly with the tether. The Gimbal will also be removed. Instead I plan to use a spare light weight PTZ camera (powered by POE) I already own one. I expect the tether to me at least 100m. The power to the camera system would be provided by DC-to-DC convertor (12v to POE/48v)

I have done the work with the camera - it works fine with 100m cable. I get crisp HD images with 20x zoom and day/night functionality. 12v DC- to- 48v DC convertor works absolutely fine. I am working on removing the entire casing of PTZ to make it light weight - have to custom fabricate carbon fiber casing for that.

I know I need at least 6 cores for the PTZ camera system - 2 for powering the camera, 2 for RX and other 2 for TX. (POE is done using cat6 cable)

Also, I have looked at the existing tether solutions - they are quite expensive and out of my budget.

Questions running thru my mind:
1. How do I replace the RC transmitter with wired control?
2. How many cores of wire I would need to replace RC transmitter?
3. Does thickness of each wire matter (other than for the combined weight of 100m cable)?

Has anyone worked on such a project before? If yes, any inputs are appreciated.
If you have a better suggestion - I really do welcome it. I am at square 1 right now and would want to start the right way.

Thanks!!

Older_Man · Jul 24, 2017

Your better off using a deep cycle boat trolling battery instead of a car battery.Weigh that 100m of 6 cores cat6 cable with a carbon fiber casing to see if your drone can lift it.

Wolfiesden · Jul 24, 2017

Wardhan said:
Questions running thru my mind:
1. How do I replace the RC transmitter with wired control?
2. How many cores of wire I would need to replace RC transmitter?
3. Does thickness of each wire matter (other than for the combined weight of 100m cable)?

Has anyone worked on such a project before? If yes, any inputs are appreciated.
If you have a better suggestion - I really do welcome it. I am at square 1 right now and would want to start the right way.

Thanks!!

#3: Are you serious or just kidding?

Honestly, I think you are missing some very very big issues with tether systems.

First is power. Those motors draw considerable current to lift the craft, let alone 100m of cable. Yes. SIZE DOES MATTER. Wire (any conductor for that matter) has an internal resistance. Resistance, any resistance, limits current through a conductor and resistance is cumulative through a circuit, which INCLUDES the return path. So any wire resistance isn't 100m long, its actually 200m long, up AND back down. You can put a lot more current through a 1' piece of 24ga wire than you can through 650' (200m) of it. The current loss at that length is going to be significant to say the least. And that loss will be converted into heat. Enough of it and the insulation will begin to break down. If I were you, I would find out how much current at full throttle your bird consumes (put an ammeter in line with the battery) and find out just how much current you will need to provide for. I think you are going to be in for a rude awakening here. Your choice to raise the voltage is a reasonable one. Every time you double the voltage, you cut the current in half. Wire isn't interested in voltage (for the most part), but it cares a lot about current. However, you will have to put a step-down capable of delivering the power needed at the top. Add that to your liftoff weight.

Next, its an antenna. Guess what a piece of wire 100m long sticking straight up from the earth is called? Its an antenna. Your cabling will be picking up lots of RF. You better prepare for it. Its going to creep into your power circuits, your control circuits and possibly damage sensitive components. Especially if you fly anywhere near any radio source such as an AM or FM station. AM moreso. And HAM. And CBs.

Next, its a shocker! Static electricity is going to be a real fun thing for you. When the bird is airborne its going to be generating static buildup via its props and wind over plastic surfaces. When its untethered, its not an issue because it goes nowhere and gradually dissipates. Sorta like a bird on a wire, 10s or 100s of KV on the wire don't bother the bird. But will make a squirrel explode if it jumpers the wire to ground. So make **** sure you protect against static discharge. Both you and your circuits.

Do you know Benjamin Franklyn? Ever here if his kite flying (rumor or not)? Guess what you are doing? Same thing. Hopefully you will live through it like he did. Many people have not. You are making a 100m tall lighting rod. There is considerable danger here my friend. Considerable. Lighting doesn't only happen when its raining (wait, isn't that a song?).

Completely removing RF (either for control or for video) may not be your best option. Yes, the airborne radio does weigh, however it weighs LESS than the cable you need to transmit the same signals.

Another option that may be leveraged is fiber optics for data. You could send every control signal, all the video and any other data/telemetry through a single thin fiber line to the ground. You still have to get power up there, but instead of relying on heavy copper to transmit limited data, consider fiber. Its not perfect, but something you should look at.

Maybe it would be good to state your END goal and not be so worried about HOW to get there just yet. I mean, why are you attempting this? Whats it get you that the current bird does not? And as far as I know, if you are trying to get around any FAA requirement, I don't think a tether will do it.

I am not trying to foofoo your project. Just make you aware that its far more complicated than connecting a wire to it and it just works. Life isn't that easy.