Releasing the Shackles Part 2 - Ground Testing

You may have seen my earlier post "Releasing the Shackles - How far do you want to go"about doing long range APM telemetry over cellular links. For the last 4 weeks I have been testing and have finally cracked the nut. Read on for details..

Amplified Engineering in Australia produce 3 potentially useful products

  • Fatbox GPRSV2 - Serial Router with  GPRS (850/900/1800/1900) - 85kbps (Dual SIM)
  • Fatbox 3G HSDPA - Serial Router with HSDPA (850/1900/2100) WCDMA and UMTS - 3.6Mbps down 384kbps up
  • Fatbox HSUPA - Serial Router with HSUPA (850/900/1900/2100) WCDMA and UMTS - 7.2Mbps down 5.6Mbps up


The Fatbox is a heavy beast at 400+ grams. Removing it from its rugged steel case is straightforward and reduces the weight to ~120 grams. I ended up halving the case and using the bottom half as the mounting bracket in my plane.

Getting the Fatbox working on a network is fairly easy. You plug it into your LAN and configure it via its built in web server. There are all the standard settings you need to connect to any compatible cell network.

The most important thing is choosing the APN, by default most cellphones are setup to use an APN that is behind a firewall. A firewall prevents anyone from connecting to the device from the internet which is what you want for your cellphone, but not what you want for telemetry.

Here in NZ the default APN on most phones is internet.telecom.co.nz however if you call the Telco and ask for the details of a non-firewalled APN, they will tell you to use direct.telecom.co.nz. The same thing works on the vodafone network, you just use direct.vodafone.net.nz instead of internet.vodafone.net.nz. It might take a few calls and escalations before you can talk to someone who knows what they are talking about and what you want to do. You might also need to have the APN added to your SIM card depending on the provider.

If you use the right APN, you will get a public IP address that is fully routable on all ports. Perfect for Telemetry. It is my understanding that every carrier in the world has non firewalled APN's you just need to ask nicely to find out the details or do a quick google search. This costs nothing extra and although it doesn't give you a fixed IP address the address you get is fully routable and not firewalled so you can connect to it from any other computer on the internet with no restrictions. The fatbox has a built in Dynamic DNS client, so as soon as it is connected, it can update a DNS alias to point to its current dynamic IP address. This means you can register a DynDNS name such as myplane.dyndns.organd then connect to it without needing to know the IP address. If your fatbox drops its connection, as soon as it comes back up, it will get a new IP address and register it with DynDNS to allow you to continue operating (other dynamic DNS providers are supported).

This works in practice as well as it does in theory. After a power cycle, I was able to connect to my fatbox over the internet after around 12 seconds.

The next challenge was getting the serial port to talk to the APM. This turned out to be a little trickier than I expected.
I ordered a Sparkfun TTL level shifter but because of the way these work (voltage stealing), it didn't work at all. There were lots of dropped packets and CRC errors. I ended up ordering a Solarbotics DTE which I did get working reliably.

I connected the Fatbox up to the APM via the DTE converter, configured the Fatbox serial port to 57k and exposed the serial port as a server on TCP port 5760. Then I loaded up APM planner and changed the drop down list from the serial port to TCP. The host name is your DNS name (or the IP address if you know it) ie myplane.dyndns.org. The port stays the same at 5760.

It connected and I was able to do everything in the Mission Planner that you can normally do. Set waypoints, configure the APM etc.... I had to double check there were no cables in the line as I couldn't believe how well it worked - Woohooo.

On to even greater things...

The Fatbox also has two ethernet ports which can be routed at the same time as the serial port. I was interested in using one of the Ethernet ports for a Pan/Tilt/Zoom IP camera to give me unlimited range video (now you can see why I ordered the HSUPA version of the fatbox).


I configured the second ethernet port as a DMZ and then opened pinholes in the Fatboxes firewall so that all the IP camera ports were exposed to the Fatboxes internet facing interface. I tried it with a Vivotek PZ6122 which is a great little camera (that is no longer made), it weighs 300 grams, has Pan, Tilt and 10 x Optical Zoom. Its hard to find a high quality PTZ IP camera in a lightweight package but this fits the bill nicely and I picked it up for a steal on ebay. This camera also works in low light and automatically changes to black and white in low light conditions. I reduced the framerate down to 15fps and set it to a fairly low bandwidth setting and it worked very smoothly over the cell link.

Now I have it all working on the ground, the next step is to get it airborne and see what sort of altitude I can get before I lose cell link. I'm fairly confident it will go to 400ft which is as high as I can legally go anyway, but more importantly, I'm hoping to get some very good range out of it. With the combination of high mountains we have here in NZ (which forces Telco's to be able to operate at altitude) dual antennas on the plane (with short cables) and the high bandwidth of the fatbox, it should be able to go significantly higher than 400ft. NZ has outstanding cell coverage so this should allow me to fly long range missions just about anywhere in the country. The Hugin airframe can lift a lot of weight so I should be able to load it up with 15,000mAh of 4S batteries for a 90 to 120 minute endurance depending on speed.

I am talking to the manufacturer of the Fatbox about maybe putting in an order for a few of these and customizing them for DIY drones use. The customized version would come without a case and have direct TTY level outputs to save messing around with a serial converter. Let me know how many people might be interested in this to see if it is worth the time.

My next post will be to report the success of the first cellular flight.

I'm also really keen to find a trustworthy person to try controling the plane from overseas once I have everything working properly, a pilot could operate it via the APM planner and see what is happening over the internet using the onboard camera. It seems like something that just has to be done!!

Views: 5519

Comment by Dez Socks on December 20, 2011 at 7:34pm

Nice i like your idea but 3g , wap etc is limited height wise as signals are usually directed towards populated areas and towards the ground >200 meters.There is no use in a isp beaming it towards the sky as it would be wasted bandwidth.It can work within a certain height i like the idea but as for live feed i know 3g has a min of 60ms lapse so that could be something to account for.Good luck grab a buddy/spotter and look forward to your 1st cellular flight.

Comment by Toby Mills on December 20, 2011 at 7:52pm

In most places it is, here in NZ we don't really have any areas of concentrated population, the population is spread out (other than 1 major city). We also have a LOT of mountains and people like to use their phones on the mountains, so it means our cell infrastructure is designed to work at altitudes of several thousand feet.

Nevertheless, the testing will be interesting and I'm looking forward to reporting the results which I think could be quite surprising.

Comment by Toby Mills on December 20, 2011 at 8:05pm

I'm not using the video for FPV so 60ms should be fine. In fact if its that low I will be very happy!!

I always think that if NASA can fly voyager with several hours of latency, or a mars probe with several minutes of latency, then I should be able to fly a plane to waypoints with less than 100ms latency.

Comment by John Hestness on December 20, 2011 at 8:28pm

Toby, this is really cool.  This could have many applications, in descending (haha) order, airplanes, helis, blimps, quads, self driving cars, walking vehicles (robots), rovers, boats, submarines. It also occurs to me that you are close to being able to extend the cell phone network or internet with your plane. 

 

That is a nice looking plane, have you flown it manually yet?  I spent some time in NZ years ago and would be happy to volunteer for experiments.

Comment by Toby Mills on December 20, 2011 at 8:36pm

I'm not sure about the legality of extending the cellphone network :)

But in theory, you could add a wireless access point onto the other LAN port and use this to provide a mobile wireless access point. In a location that had no coverage on the ground, but by elevating could get coverage, you could provide internet access. Interesting idea.

Yes, the airframe has 4 manual flights and a couple of stabilized flights under its belt. I have a blown XBee and as they are all out of stock everywhere, wanted an alternative so I could tune in the air. It just needs a little bit more PID tuning to get it flying nicely. Its a very stable platform.

Comment by Dez Socks on December 20, 2011 at 8:55pm

60ms min depending on coverage on 3g.Enough for me to kick some butt online on a xbox live .Sorry this idea is a bit late but if you were say you were to buy a 3g edimax router (think made in Australia), and dongle then you could have the same as but as stock mine weights around+/- 100g+ dongle approx 20g with all cases no serial ports but 4ethernet ports out 1 dsl in 1usb in for dongle and wifi built in.think its less than 12vBut then again the backup for the dual sim is not there.What bands does the box support?As in i have a quad band phone i can use it in 4 continents.I live in Ireland is that far enough!!!


Developer
Comment by Randy on December 20, 2011 at 8:56pm

This is a great post.

I'm interested in this sort of thing for Japan because there are very strict rules on the power that can be used for wireless connections and because of this FPV is legally impossible.  On the other hand the phone network reliability and range is 2nd to none!  I had been thinking about using a phone drone for a similar purpose although I'm not sure if that's possible or not.

Comment by Dez Socks on December 20, 2011 at 8:58pm

Also as randy says phone drone altho i see no programs or projects as of yet, cheap android phone has it all

Comment by Eric Marc-Aurele on December 20, 2011 at 10:19pm

I'm interested; assuming it has enough documentation to make it close to turnkey I'd buy today.


100KM
Comment by Hein du Plessis on December 21, 2011 at 7:50am
Hi Toby I'm very much interested in buying such a device for my application and if you can prep it for APM, all the better! Ill also be happy to test drive your AUV from here in South Africa, we're also right-side up ;)

I'm just a little concerned about noise induced into the servo etc wiring. Do you see this as a problem? I've heard horror stories....

Good job BTW!!!

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