What is the maximum range of an Xbee? - Lets find out...

I have recently been pushing the limits of the XBee Pro to see how far it can go.
Unfortunately my current plane (SkyFun) only has a 38 minute duration and a maximum travel distance of 20km, this means the furtherst I have been able to go is 10Km (a 20Km return trip).
I have a 14dB patch antenna which has still shown signal of 85%+ out at this distance.

I wanted to find out how far the XBee could really go.
This meant planning a one way mission.

I spent about a week looking for the perfect start and destination, plotting the course and arranging access to the landing location with a local farmer.

The start point was my normal local park and the landing location was a farm paddock 16Km away.
The flight was over sparsely populated farm land and at a constant incline meaning I could increase altitude during the flight in order to get greater range.

My plan was to launch and monitor the flight from the launch location until I lost contact with the plane via Telemetry. After this I would drive to the landing location where the plane would be circling and manually land.

I calculated that even if I maintained contact with my plane during the flight and it made it all the way that I would still have time to make the 12 minute drive without running out of battery power.
With a tail wind, the plane would average 60Km/h at 45% throttle.

With everything planned and 45 test flights already in the bag with this airframe I was ready.

I launched and the plane took off to the waypoint as planned.
I was hoping for at least 12Km as this was ideal conditions.
The point on the map above shows the point I lost contact which is 10.6Km from the launch location.
The XBee maintained a very strong signal up until the last Km and then it began to drop off very rapidly.
It begins to be unusable below about 40%.

I packed up the ground station and drove to the destination which took just 11 minutes.
The plane was circling perfectly as expected and I put it in FBWA and landed without incident (apart from the slightly startled flock of sheep).

It turns out that the 10Km I had been flying to is around the maximum range of an XBee.

I am working on a much bigger aircraft that will have a 1 hour plus duration at a higher speed so I am going to have to look into more long range options for telemetry. GPRS / cell is preferable as we have excellent coverage here and fully routable and cheap internet plans. However, for experimentation I have been surprised at the distances that can be achieved with an XBee with a cheap patch antenna added on.

Here are a couple of tips for people wanting to achieve maximum range..

 - Minimize antenna cable length. My XBee is mounted on the back of my patch antenna and I run a long USB to my laptop. This maximizes gain and reduces lost signal.
 - I use either the ground or my car to enhance the ground plane effect. Putting the antenna in front of my car door or right beside my car makes a big difference to the distance. Also keeping it as close to the ground as possible.
 - Altitude is king, the higher you can fly the greater the achievable distance. Due to the fact my destination was on an incline, my end waypoint was 400m high relative to my starting point.
- Fly long straight missions so you can line up your antenna properly, I am building an antenna tracker that removes the need for this but Ardustation2 is currently broken since the last Mavlink updates.

Views: 41300


Moderator
Comment by Grips on October 8, 2011 at 7:24am

Has anyone contacted industry Canada about using the DIYDRones kit legally in Canada?


Moderator
Comment by Sgt Ric on October 8, 2011 at 8:25am
Theres nothing illegal about APM!
If you behave like a jerk and fly dangerously, its you who are breaking the law... NOT the equipt!

That was a ridiculous question!

Canada has similiar restrictions on freq use as well as proximity to airports, altitude limited to 400' same as a kite, and need for a COA for commercial use, etc.
Not much diff from the U.S.
Comment by Manoel de Deus Mascarenhas Filho on October 8, 2011 at 10:07am

congratulations, Mills was a good job and with valuable information. It will help many. Thank you.


Moderator
Comment by Vladimir "Lazy" Khudyakov on October 8, 2011 at 11:43am

I flew for 2,3 km with XBee Pro ( 2,4 ) without any problems...

http://diydrones.com/profiles/blogs/short-range-flying?xg_source=ac...

Comment by Toby Mills on October 8, 2011 at 12:23pm
Jeb, jose.
I only use my RC for landings.
The default startup position for my arduplane is FBWA.
I have RC failsafe disabled.

I turn on my plane, connect with my laptop, load my waypoints and when I am ready put the plane in auto mode. Then I just throw it. You do not even need to use the auto takeoff feature in APM.
The launches are far more stable, reliable and safe that you can achieve in manual mode.
I have my RC on just in case but as soon as it's on it's way I turn off my RC tx.
When it's time to land I make my final waypoints a loiter above my position then I turn on my RC tx and change to FBWA and land.

I should note that because I have such a huge battery on my skyfun that the plane is incredibly unstable and almost impossible to fly in manual mode. Eventually I plan to get rid of the RC system altogether and use the joystick through mavlink but there is a lot more testing to do first. I feel the sooner we can remove our dependance on RC and rely more on the automated systems the more like real drones the platform becomes.

You don't see an army geek with an RC tx standing next to a reaper:)

I think the RC system generally adds more risk and reduces safety. It allows for the opportunity for interference and it's more components to go wrong. The sooner I can get an RC tx out of my plane the better!!

3D Robotics
Comment by Julian on October 8, 2011 at 1:11pm

Does anyone know of a MS lag time for transmitting over a distance like that? Im working on a project thats looking to do processing at the ground station level and send flight commands back to the airplane, wanted to see if this is unrealistic or not...

Comment by Greg Fletcher on October 8, 2011 at 3:06pm

@ Julian,

 10 km / (299.8 km/ms) = 0.0343 ms.

    You would never see it.

Comment by Toby Mills on October 8, 2011 at 3:14pm
@Greg.
I suppose it depends if you consider your project an RC plane with an onboard autopilot or a drone.
Personally, I have other models I fly for the joy or RC but for this project I consider RC as an unfortunate backup that must be used. The title of the site is "DIY drones" not "DIY RC models with autopilots" :)

If the autopilot is built with enough redundancy and smarts then you should never need to use RC. It's a safety net many people struggle to let go of but I have done over 40 flights only using the RC link to flare for landings. If we got sonar working it would not be needed at all.
Comment by Greg Fletcher on October 8, 2011 at 3:15pm

I would never give up the RC link. I would enhance it(dragonlink ?). Going thru 2 computers and Xbees also leaves a lot to go wrong as well as adds control latency. It's not the distance, it's the processing and Xbee. I would always want a hardware fail safe,but hey, that's just me.

Comment by Greg Fletcher on October 8, 2011 at 3:46pm

The big boys with the predictors and reapers land and take off locally because of the latency of the satellite link. Different cause, but same result, control lag or latency. All most guarantied to cause a PIO (pilot induced oscillation).

 

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