Sky Anchor Smart Drone, Wifi / SDR w Tether

Smart tethered drone has unlimited flight time, onboard Raspberry Pis, machine vision tracking and robotic directional Wifi antennas

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Sky Anchor is a Smart Raspberry Pi 4 powered drone. Robotic targeting of remote long range AP allows solid connection even in the wind. Using servos and machine vision Sky Anchor can find and target a remote long range WIFI AP as well as Software Defined Radio communications for missions in remote areas or disaster situations where typical cellular connections are not available or poor quality. A ground facing Machine Vision camera to tracking the base station and compensating for GPS drift.

This is an Open Hardware, Open Software Project, certain software may be open but not open source code however free to use.


I love robotics and look forward to creating more public service robots like grounds keeping and security robots, that being said they benefit heavily from a high speed internet connection with unlimited bandwidth. Telemetry, GPS tracking and video recording are all essential aspects of robots in public or robots that operate without up close supervision like a rover.  Cellular speeds have been on the decline and there are no high speed unlimited hot spot plans that will fit the bill. I really needed a way to get fast network connections ( and possible open internet connections) to a robot far away and avoid obstructions to check on projects and download data.  Small budget groups that need to get a high speed internet connection anywhere outdoors ( or indoors with a little more wiring) can benefit from a cheap, modular, swappable payload, instant antenna mast system.

In comes Sky Anchor, this allows myself and anyone else who duplicates this project to have a rapid deployment sky born communications for both Software Defines Radio, wide area wifi ( below the drone) and the ability to target a robot or AP off in the distance and lock onto that direction and angle and adjust if the AP is moving. This is where the smart part of the drone is important using machine vision and Software defines radio to track projects or locations that need a solid internet connection to transfer data.

This Projects Mission is to Provide an OPEN BUILD, 3D Printed parts, using OPEN Hardware and Open and /or free software for the maximum repeatability. Sky Anchor empowers amateurs to have an instant sky platform for instant long distance communications.

Special Features

1. Ground Facing Machine Vision Tracking to compensate for GPS drift.  On the Ground there is a beacon the camera tracks, giving the computer info to adjust position relative to the ground.

2. Downward Facing LIDAR to measure altitude from ground level beacon, to hold height 

3. Camera and Antenna Gimbals Locking system, Machine vision sees a light in the distance and locks the antenna angle on that long range target. This keeps alignment in the event of heavy wind.

4. X6 Hex arrangement, Custom 3D Printed arms and mounts to double up the motors and props on each arm. This gives Sky Anchor 12 props and 12 motors for exceptional lift and control authority in heavier winds

5. RGB light ring around the Drone, not only is this for visibility ,but someone who needs to align their antenna towards Sky Anchor can easily see it in a "North Star" approach.

6. 110-240v power tether from ground to the drone

7.  Cat5 shielded cable from ground to drone.

Basic Equipment List, needed for the project:

1.   Ultralight 500 watt AC to DC power converter 187.87

2.  Transmitter and Receiver 6 channel TBD

3.  Backup battery 3S $40

4.  110-220v wire tether 200 foot TBD

5.  Shielded Ethernet  200 foot TBD

6.  5G Long Range Antenna $60 TBD

7.  Pix Hawk $90

8.  GPS antenna $40

9.  Rasberry Pi 4  x2 ( have it)

10. Rapsbrry Pi Camera x 2 (have it)

11. 3D Printed custom Mounts and Dual Motor Arms

12.  RGB strips controlled by Raspberry PI

This is not comprehensive, but is a basic list to buy.

i. Concept

A. Is the project creative, original, functional, and pushing boundaries? 

B. Does the project effectively address the selected challenge?

Field Ready > A. YES! not specific to the open challenge example , however having rapid deployment internet and radio communications where cellular signal is either poor or cell network is not suitable for high speed communications between base camps / facilities. This is particularly useful for private use and disaster response.

Conservation X Labs> A.YES!  B.YES! Using  additional downward facing cameras and polarizing lenses to see below the surface, conservation...

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  • Soldering the power distribution

    Josh Starnes7 hours ago 0 comments

    I really am not sure if I have the worlds worst solder or this soldering gun is giving up the ghost. I went through three tips and a bunch of flux. As far as looks go, this is not my best looking soldering job, but I went through and reheated each connection to molten and then cooled again to prevent any cold joints.

  • Bending Arms for Storage

    Josh Starnes18 hours ago 0 comments

    This is the fold down mount for the new arms. We already needed to design a new arm to mount two motors and props on each arm , so adding a folding feature would make it easier to store and transport as well.

  • Reaming the props for perfect fit

    Josh Starnes5 days ago 0 comments

    This is sort of uneventful, but there are tedious tasks you need to do when prepping any aircraft. Reaming custom props to match your motor shaft perfectly with no play is one of them. I picked up a reaming tool typically used for wood from Great Planes. The shaft of a DJI 2212 is just shy of 8mm thick when measured by a micrometer.   Because of the motors that will be pointed down in operation, there are no DJI self tightening props that will work. I actually need to Ream the props and mount them in reverse to be in the correct orientation. Also moving from 9.4 in x 4.5in to 10 in x 5 inch provides a bit more thrust over the original props.

    I have finished reaming and matching props to the motors. Next I need to balance then on both blades as well as the hub. More on that soon...

  • 1st step prepping power supplies

    Josh Starnes5 days ago 0 comments

    They he first steps in prepping the power supply boards after the case has been removed. A more open design means more airflow as well as adding more active cooling. The specs say the board is rated for 500 watts ,but the specs on the board indicate 600 watts. Usually to get the most out of a power supply you need a good cooling solution. Three things allow this, a heat sink, open airflow and forced air movement on the heat sink and board. Given this is mounted under a drones 12 props air movement is in abundance. We really do not need a fan dedicated to each heat sink. I may reorient the heat sinks so that the canes are vertical, but I am guessing this will make little difference given how turbulent the air will be moving. 

  • Two 500 watt power supplies

    Josh Starnes07/30/2020 at 03:48 0 comments

    here are the two power supplies with the aluminum casings removed to reduce the weight. 

  • Destructive testing

    Josh Starnes07/27/2020 at 06:15 0 comments

    Ok so I have been testing out the dual motor design to find the points of failure. I use 8 pounds pulling from the end until the arm snapped about a inch from the end. Inspecting it further I can see this is for two reasons. One , because it is the greatest point of stress from a leverage position. Second, the plastic is also the thinnest here out of the entire arm design, which leads me to think I might need a bit of design modification to strengthen this area. I could do this by moving the vents a couple of mm away from the edges to thicken the side walls. Also I may add a side edge lip along the bottom.

  • Motors mounted x config

    Josh Starnes07/27/2020 at 01:21 0 comments

  • Lots of prints

    Josh Starnes07/27/2020 at 01:19 0 comments

    I have several of the arms and joints printed with 4 shells and 15 percent infill.  I printed extra in case of defects from 3D printing or just accents like a minor crash. 

  • Cooling turbine for motors

    Josh Starnes07/23/2020 at 03:41 0 comments

    There are two versions of this, one CW and other CCW

  • Long Endurance Cooling Options

    Josh Starnes07/23/2020 at 00:25 0 comments

         One issue we must address is endurance running on these motors. Many pilots recommend resting between every few flights for cooling. This may just be superstitious for those who know they are pushing the limits of their motors with heavy weight or higher voltages to the motors like a 4S 14.8V battery instead of a 3S 11.1 that they are engineered for. Splitting the load between 6 or even 12 motors reduces individual motor load and heat. In addition DJI and other companies have added cooling solutions, on the new generation motors, that pull air from the bottom up through the motor. Some also have small heat sinks on the base plate. That being said I will try out both approaches. First being a 3D printed centrifugal fan that slides onto the shaft under the prop, this will need to be balanced just like a prop. Second is cutting down a 40mm x 40mm aluminum heat sink into a round shape to act as a base plate under the base of the motor. This will further draw heat away from the core magnet wire winding. This is where nearly all the heat is generated in the motor. The base powder coat will be removed and heat transfer paste applied. I will bench test both of these on 50 percent, 75 percent and 100 percent throttle for 10 minutes to see if we have heat soak differences with and without the cooling solutions.

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target drone wrote 07/05/2020 at 23:09 point

As the weight of the copper is likely to be the most constraining aspect, consider using step up/down transformers to send a much higher voltage over thinner conductors. As described, 120V @ 30A for 200’ would require 50 pounds of stiff 6 AWG copper. If you up the voltage to 480, the current drops to 7.5A, and you could carry the same power over about 4 pounds of nice, flexible 16 AWG. 

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Josh Starnes wrote 07/06/2020 at 07:16 point

I appreciate the idea, but do you have suggestions of how to do that, what would I use?

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helge wrote 07/09/2020 at 09:17 point

1) leave galvanic isolation, rectification and PFC on the ground. Create 350-400V DC (don't worry too much about that, can always start with a modern 1000W ATX power supply and tap off the DC link capacitor + proper filtering, RSHN series filters maybe)

2) use heavy power filtering

3) use a quasi-resonant, non-isolated buck converter on the hexacopter (non-isolated:, isolated:, they can also be paralleled with load sharing)

4) with appropriate filtering on both ends, you can also use HomePlugAV modules, without the 50/60Hz mains sync they generate their own synchronization (I used the ones from BEL in a project, excellent performance and support

good luck

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Josh Starnes wrote 07/09/2020 at 06:26 point

I moved to a 120 volt tether, with a switching step down 500 watt RMS power supply , the Power supply is 1.5 pounds and the power tether is a little over 2 pounds. I think I will move to an copper clad aluminum 16 gauge power wire.

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Neo wrote 07/04/2020 at 19:13 point

Very interesting project. I hope you get somewhere with it. I was thinking of a similar solution for quick surveillance of sites.

As some have very eloquently and expertly pointed out, the power system will be crucial. I also see issues with the motors, you need to find motors that are reliable enough to run for hours on end when they are designed to run for 30 minutes tops. If you go for a hexacopter, losing a motor would be less of an issue, but if you go quadcopter it would mean a crash. Changing motors out could drive the cost of maintenence up a bit.

I remember NASA had some similar concept a while back, but now it's using tethered balloons. Seems a bit easier that way since they just stay up there without moving parts.

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Ethan Waldo wrote 07/03/2020 at 21:20 point

Meant to say monocrhomatic light source

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Ethan Waldo wrote 07/03/2020 at 21:19 point

Great idea.  A much more difficult feat to pull off that wouldn't require the tether would be lightweight solar panels as the base pointing down.  Generate a light source from the ground and use mirrors to focus light to illuminate solar panel to maximum efficiency.

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KD9KCK wrote 07/03/2020 at 20:41 point

This is very interesting. I wonder if you could also use this type of tether to lift up the end of a vertical HF antenna. 

Also as a WiFi access point you could have it extend a AP that exists at the base station up to it, that would make the access point set up cheaper. Seeing a an AP that takes Fiber or a Fiber to Ethernet adapter is going to cause a good amount.

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BotLawson wrote 07/02/2020 at 04:58 point

A couple of comments from when I built a big tether at work. 

Your power tether needs a high surge power capability as current flight controllers are designed for batteries which have tight energy budgets, but loads of surge power capability.  Most power converters for a tether have exactly the opposite limits with "infinite" energy available but a fixed rigid power limit.   (re-coding the flight controller to stay in a power budget would be another option)

There is/was a chineese drone company that makes 400Vdc motors and controllers. looks like what I remember, though it's not loading.   (still alive on facebook )  Fun fact about motors and controllers, for a given power a 40Vdc and 400Vdc motor and controller is about the same size.  So ideally you just run the motors directly off the high voltage tether.  This also allows battery backup to stay on the ground.  Also the typical DC link voltage in a active power factor correction AC-DC power brick is 300-350Vdc so it's easy to get high power non-isolated supplies near 400vdc.  (oh, and these same universal AC-DC power supplies often happily run off of 100-270Vdc as well, some are even rated for HVdc input.)

The next best would be high voltage high frequency AC so you can use a small ferrite core transformer and diode pack to make low voltage DC on the drone.  100KHz to 1MHz would do.  But keeping emi and rfi in check will be a challenge.

Mil spec M27500-22RC2S09 high temp 200C 600V 2-core shielded wire is a good place to start.  The shield is a bit heavy, but makes a solid safety/lightning ground.  And the cable comes with 26awg to 8awg or lower conductors.  Aluminum wire will save you weight, but is more difficult to make reliable connections to.

Speaking of lightning, you should also be able to monitor ground current to estimate your lightning risk.  Check Wikipedia, but lightning storms have 1000-10,000x higher electric fields that most clear air, so if your ground current jumps to more that say 100x typical, you can be pretty sure a storm is nearby. 

For communication, home AC wiring Ethernet bridges will work great and be very happy to use a shielded twisted pair vs AC wiring.  (lots easier than finding tether wire with conductors and a fiber-optic) 

Finally spooling the wire.  The wire is going to get hottest on the storage spool.  You'll want to wind it in a way that you can keep it cool.  I eventually wanted to wind the wire with a fishing reel or yarn ball-winder mechanism as these can wind in a sparse pattern for wire cooling and potentially eliminate the need for a high voltage slip ring. 

Finally Finally, I'd look configure your drone like the endurance record drones featured in some YouTube videos.  They can get >2h flight times on LiPo's so should minimize the tether power system size. 

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Dan Maloney wrote 06/24/2020 at 00:27 point

I had an idea to use a drone to take a small amateur radio repeater aloft to get line-of-sight between two points in mountainous terrain, rather than put up a tower. Flight time limits would have made it only marginally useful though. I hadn't thought of tethering it like that - clever move.

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Josh Starnes wrote 06/23/2020 at 21:31 point

Thanks Bill, Yes one of the uses is lighting. I intend to 3d print a ring that will house 50 watt 6000k LED modules downward pointing and RGB LED array all the way around the ring. In the event high speed communications have too much interference, or one party away from camp does not have a mobile base station, they can also communicate through a morse code style short message by blinking the LED horizontal lights and the field crew only needs a bright light to reply to the Sky Anchor.

I do intend to do a higher voltage, I was thinking of a 110v line straight from a power conditioner up the power line tether.

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James Hall wrote 06/29/2020 at 19:00 point

You could do a Close Encounters like thing with the LEDs.

Alternatively, I've seen pages talking about doing long range free space optic style communication by modulating LEDs. That would be neat to see. is one site.

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billguetz wrote 06/23/2020 at 17:02 point

Interesting.  Some thoughts:

- it could also be used for temporary lighting

- it would be useful even if it didn't go up 100' ,  think tree canopy.

- high voltage power would require smaller cable, but increase safety concerns

- wind is major limitation.  tilt of platform due to wind may limit usefulness without stablized platform

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