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Rtk on a budget

133K views 411 replies 52 participants last post by  JB_1 
#1 ·
So after going thru a few other threads I've decided I'm going to try to come up with a cheap rtk setup for my spray tractor and for use in a ute when towing a weed wiper (which we are in the process of making). I will be using a tablet for my guidance display (using either a commercial app or agopengps). I am aware it's only guidance and why would I bother with rtk and only L1 for that matter? I like a bit of a challenge and with what I'm thinking of using it will hopefully work out cheaper than a novatel receiver. As much a novatel would be nice and easy, it is stretching the budget and I can get as good accuracy with hopefully a smaller price tag.

So the plan is....either a drotek tiny rtk receiver setup (thanks for torriem for putting us onto it) or an Emlid reach rtk setup using a jdrone rf900 plus long range as radio. Both of the receiver setups are gnss enabled so will make use of beidu etc. They will hook it into my tablet to feed it nmea strings. Currently all of this technology is being used in drones/uav's so with a bit of luck it will be a case of plugging each item in to configure it, hook it all together and then turn it on and away we go. I realise it will most likely entail a heap of stuff around, playing with different settings to get it going but I've got a plan which is the main thing.

Autosteer/rate control might come down the track but I'm not worried about that at the moment.

Don't expect this to be fast moving because getting parts shipped to aus may take a while, especially if I order the wrong thing because this is my first electrical project.

Any comments/suggestions are appreciated.

Cheers
 
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#3 ·
Awesome, one more piece of the puzzle.

Make sure the tablet you get can charge while it is also using the USB. Its a limitation for many tablets.

AgOpenGPS runs only in Linux and window$, but tablets are couple hundred bucks, and then you have another tablet anyways.

Looking forward to following this.
 
#4 ·
Theres heaps of tablets running windows 10...if u want cheap or to check out.

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Ive used ali and gearbest sites...works fine..

I like the techlast tabs

Alot of dual boot with windows and android...trick is u cant update any versions..

Ant...
 
#8 ·
Dual boot would be handy. Apart from on my PC, I've never used a windows tablet. Mind you, I've got an iphone and iPad so no exposure to android devices either. Is there any advantages in either windows or android os's? I've had a look at the irulu tablet (mentioned in agopengps thread) I am aware agopengps only runs on windows but there are plenty of apps already out there for android.
 
#5 ·
So I've been doing some research. The emlid reach rtk (which uses the same chip as the drotek tiny rtk) looks like it might be a good option. It can either communicate via serial or Bluetooth so depending on what else the tablet is doing you should have some flexibility. A emlid reach setup is $570usd so it's going to be the dearest part in the project I think (depending on what tablet/s I get)

I know my autofarm A5 rtk runs on a freewave fgr 900mhz radio. I'm aware of pacific crest and satel radios being used on other systems but these are horridly expensive. I'm trying a Rf design 900+ 900mhz radio which are reasonably affordable. It may require a bit better antenna in order to get good range but that's alright imo.
 
#6 ·
Our Fieldnet pivot system uses off-the-shelf 900 Mhz radios to communicate for several miles (the base station can go about 6 or 7 miles). I think they use normal XTend 900 Mhz modules, 1 watt.

Another possible solution is a simple app on a cell phone that communicates via the internet with your base station, and talks over serial or bluetooth to the RTK receiver. A bit more complex though.

I have a couple of Trimble integrated autosteer units, currently using just WAAS. I know that the steering computer actually talks over RS232 to the receiver, but it uses a proprietary trimble protocol that is partially documented. But I was thinking that an arduino could intercept data from the receiver, decoding it just enough to find the frames with GPS position data in it, and then substitute data from the RTK receiver, and then pass it on to the nav computer. The nav computer would still think it's using WAAS, but it would be fed a very precise, repeatable RTK signal.

Basically I'd love it if I could use a cheap RTK receiver to provide navigation data to existing autosteer solutions that I already have, but unfortunately everyone is all proprietary and locked up so that they can cash my checks each year.
 
#7 ·
Our Fieldnet pivot system uses off-the-shelf 900 Mhz radios to communicate for several miles (the base station can go about 6 or 7 miles). I think they use normal XTend 900 Mhz modules, 1 watt.

Another possible solution is a simple app on a cell phone that communicates via the internet with your base station, and talks over serial or bluetooth to the RTK receiver. A bit more complex though.

Basically I'd love it if I could use a cheap RTK receiver to provide navigation data to existing autosteer solutions that I already have, but unfortunately everyone is all proprietary and locked up so that they can cash my checks each year.
The rfdesign 900+ radio is a 1 watt radio which looks very similar to the xtend radios. I checked out the whole correction by cell but it's a fair bit more complicated.

A lot of screens now will accept GPS from an external source so in theory you should be able to use this setup to stream rtk into your existing autosteer screen.
 
#9 ·
I have both ipad and android...hate ipad witha passion..clunky POS...it was a left over from the divorce...will be a dinner matt soon...

Acer have an R3 and A200 tablet that i think takes charge and has usb at same time

Chuwi Hi12 Tablet PC-259.89 Online Shopping| GearBest.com

I like this tablet, ive been looking into for a while, i need to charge and out put at the same time, for my IK multi media guitar dongle, nothing worse than practicising and then stopping to charge, it chugs the power when using the dongle as well...

I would also like split screen, the surface pro splits 4 ways, 2 would be handy...that way you can be streaming in live data while doing the job...for guitar 4 would be neat, 1 for ik app, 1 for youtube lesson, 1 for tab pro, 1 for whatever...the BOM....but its $1,100 and battery life is crap apparently.

The only downside to dual boot is updates, the wondows 10 is designed to work with that android system and thats it...might not be a biggie?

Ant...
 
#10 ·
Can't see the windows thing being an issue. I think I will order one of those today ant. It's not like it's $1000 like an apple or Samsung tablet. Will see how it goes.

Also going to order a emlid reach rtk kit. Gone this way over the drotek tiny rtk because the emlid has Bluetooth and wifi connectivity as well as serial. Just a bit more flexibility.
 
#14 ·
All components are ordered :)

Emlid reach rtk kit
Rf design 900mhz radio kit
Chuwi dual boot tablet

Going to get a weatherproof enclosure for base GPS and radio to go in and a pretty box of sorts to go inside the tractor cab. Will try to do something similar to a uhf radio aerial for the rtk radio.
 
#16 ·
As cool as it would be to 3D print an enclosure, I've gone the cheats way out and bought one off eBay. Also ordered bulkhead cables for each necessary connection to make it fairly weatherproof. From what I'm lead to believe the emlid reach unit uses a mcx connector, which isn't my connector of choice but I might have a way around it yet but we will see.

Cheers
 
#17 ·
So after a long day servicing a windmill that wasn't pumping, I arrived home to a few surprises sitting on the kitchen bench. The emlid reach rtk kit and rf design 900+ radios have arrived :) i only opened boxes and had a look, didn't plug anything together but the emlid community has a crapload of threads on hooking reach units up to radios which will be handy. There are some YouTube clips but they tend to use 3dr radios. I didn't realise just how small they actually are until they arrived, dimensions listed on a website are hard to comprehend when it's so small. I've reused the lid off my beer as a reference to give people an idea. Once I start plugging things together and mounting things up it will get a little more interesting.
 

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#28 ·
The quality of those antennas look really questionable to me. In 2013, I bought some low cost RTK hardware from OptimalSystem.DE. The receivers use the NVS NV08C-CSM module. The antennas were a Tallysman timing antenna. Hagen Piotraschke from OptimalSystem packaged the receivers in a nice water resistant enclosure with good connectors and also sent cables for everything.

For software, I used RTKLIB running on cheap laptops. I had some difficulty getting a fixed RTK solution but when I finally got it, the accuracy of the system was amazing. For a wireless link between the rover and the base laptop, I used the tethering on my cell phone. The amount of data being transferred is quite small and as long as I had good cell service, that worked fine. Using a mobile cell booster made a big difference when cell service was poor.
 
#22 ·
I'm hoping thatit will be able to get it outputting nmea strings. After spraying a paddock today without any gps or foam marker (yes I did say foam marker, stupid antiquated POS didn't work either.), a 13ha paddock with 2ft tall grass to be cut for silage tomorrow, ended up spraying 20ha and I'm not even sure I got it all, couldn't see any wheel tracks so fairly safe to say major disaster but it'll be all good. I'm going to get this thing going soon but it's a case of waiting for all the bits and pieces to arrive. That's the only bad thing about ordering cheap gear out of china is waiting for it to arrive (if I need something straight away I will use local people and quite happily pay the premium).

My chuwi hi12 tablet arrived yesterday which was good. It seems pretty good for a ~$350 tablet. 64gb, 2usb ports plus mini usb for charging. Only wifi but I can hot spot it to my iphone. It's dual boot so comes with windows and andriod so can load it up with apps etc.

Just wait for enclosures and cables etc to arrive and then get it all put together and it will start getting real. Might even be heading down the arduino track for a few different projects but that's for another thread.
Sorry for the bad flash reflection.
Cheers
 

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#26 ·
Some of the chinese tablets have microsoft surface pro 3 screens, when microsoft move up to next model they must auction off the design etc...or get paid per a license agreement..to some of the chinese tablet producers...they dont have to pay for research eyc so its a good deal when servicing there market and a bit more lower end price market....i hope they get the surface pro 4 screen as it has 4 way split.

So then you could do the following all at once.

1. Guidance screen
2. Watch Donald Trump victory speeches on you tube
3. Surf the combine forum
4. Observe weather radar

Thats effeciency right there !!!

Ant...
 
#27 · (Edited)
The tablet I bought to run AgOpenGPS on is an Intel CPU that runs normal Windows 10. I can run it in Tablet mode it does the apps full screen, or in halves or quadrants. In desktop mode it's normal overlapping windows. In some ways it's the best of both worlds. I am not a Windows person but I was actually quite impressed how usable Windows is on a tablet, and I like being able to switch back and forth between tablet mode and desktop mode.

So I don't think it matters that it has the same screen as the Surface Pro 3. I think this is all just a matter of Windows 10 itself. Though the SP3 screen would be nice and super high res, running in HiDPI mode. Whereas my tablet is just normal 1280x720. My complaint with it is that since it doesn't support HiDPI mode, it's hard to get my fonts to be readable without applying a custom scaling factor. And the wifi is really crappy on it too. Flakes out all the time and won't connect until I reboot my router, which is odd since none of my other devices or computers have a problem connecting to my router.
 
#30 ·
I was not using the output for guidance but for mapping and surveying. I wrote some custom software in Python to take the output from RTKLIB and record it or display it for survey purposes. I'm not sure if there is a way to make a NMEA-like data stream from the RTKLIB calculated position. So, depending on what you want to do with the RTKLIB output, there might be custom programming involved.

Getting the receiver modules configured, setting up serial ports, configuring the zoo of RTKLIB options took quite a lot of time. I would not expect the average farmer to have any hope of figuring it out. If anyone has capable receiver hardware and wants to try RTKLIB, I'm happy to share what settings I was using.

However, I was really excited to see that the potential is there. We need hardware companies to make receivers that output raw measurements. There are a few of them out there now. We need software, preferably open-source, that takes the raw measurements and computes a position. RTKLIB really does work and it is amazing that it is basically the result of one person's effort. I'm sure companies like Trimble and Hemisphere have vastly better software algorithms but the prices they charge for RTK drastically limits its application.
 
#31 · (Edited)
That sounds great. I think my main interest in RTK is for mapping (elevation and drainage) at the moment, but feeding a system like AgOpenGPS and steering would be useful too.

I imagine that the RTKLIB position data could be turned into NMEA strings with a bit of Python code to calculate speeds and headings (would require some filtering). And maybe add in some data from IMU sensor for compensating for tilt. Doable I think. A SBC like a Pi should have enough horsepower for this.

I think I'll pick up a pair of receivers I can work with this winter and then I'll ask you for some more specific details of how you did your setup. Would be nice to have a turn-key solution for cheap RTK that is just a matter of basic setup and plug it in and go (with NMEA output). Step at a time I guess.

EDIT: Looks like RTKLIB's rtknavi and rtkrcv programs can emit NMEA strings (GGA and RMC), but only at 1Hz. But I think that's an arbitrary limitation for compatibility with other applications. Also looks like there's an Android app that contains RTKLIB (requires external GPS to the phone or tablet) that can provide location for Android apps.
 
#32 · (Edited)
I see based on the emlid.com, those are Tallysman antennas. So, I think they are probably quite good given their low cost (about $60). You can buy a higher quality antenna like I have from Digikey but it is about 155 CAD.

Here is what seems to be a up-to-date list of RTKLIB supported hardware. The emlid hardware uses a u-blox NEO-M8T module. I think my older NV08C-CSM has some quirks and maybe the u-blox module works better. If you don't need the on-board microcontroller the emlib device has, you have the option to buy a NEO-M8T connected to a USB interface. Then you would run RTKLIB on the USB host computer (e.g. a laptop). One cheap module I found is 66 USD. No enclosure so maybe good enough for experimenting but not really for field use.

I see OptimalSystem.DE has a bunch of new hardware they didn't have when I was shopping a few years ago. For example, RTK base-station with 433 MHz radio and 10 Ah battery, u-blox M8N as ruggedized Bluetooth device with dual DC power supply and high-current USB charger jack, without GNSS antenna, NV08C-RTK as Bluetooth rover (with antenna) for rooftop mounting.

The NV08C-RTK is something new I hadn't see before. It looks like it does RTK internally so you don't need RTKLIB running on a laptop or micro-controller. If it works reliably, that's really cool. The cost of the basestation is about 1000 EUR. Not trivial but also only about 1/10th the cost of other RTK receivers I have seen. If you could get some neighbors to share the basestation, you could split the cost.

Edit: I should also note, you are getting quite a bit for that 10x cost increase on a better basestation. For one, a basestation from Trimble or Hemisphere or one of the big GNSS companies will probably be dual frequency RTK. All of the low cost RTK hardware that I'm aware of is single frequency (L1) only. As I understand, dual frequency gives you much faster startup time (RTK takes quite long from power on until a fixed solution). It also helps in situations where multi-path signals from the sats is a problem (buildings, trees, wet soil, etc).
 
#36 ·
The accuracy you get from a single frequency (L1) system should be very nearly as good as dual frequency systems. Single frequency systems can certainly have mobile rovers. The Outback Baseline-X system is basically a single frequency RTK system, as I understand it. My brother has one and it preforms very well for guidance.

Again, dual frequency systems will have faster warm up times (integer ambiguity resolution has more known values in the equations). I understand they are also more accurate at long baseline distances. The atmosphere affects different frequencies differently and so the receiver can deduce better corrections. They also can more easily deal with multi-path effects.
 
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