Dual Antenne vs. Single + IMU

[TeddyStamford]

I’ve run Single F9P and BNO085 IMU for the last three years and been very pleased with the results, steers very smoothly, very straight and with very low XTE.

Decided to try Dual antennae as there was a suggestion it maybe the way future AOG development heads (since decided that Single and Dual will both still exist).

So made another AIO with two F9Ps and put two antenneas on the cab, utilising the cab lifting points as mounting points, this gives antennea spacing of 146cm.

Dual uses the right hand antennae for position of the tractor and the left is used to calculate the heading and also together with the position antennae acts as the IMU, by calculating the height difference and the distance between the antenneas the angle of roll can be calculated.
One of the problems with the BNO085 IMU is its affected by sideways acceleration, so if you turn sharply or go over very rough ground the angle of roll is exaggerated, in my testing turning sharply caused the roll to spike by 7 degrees and going over bumpy ground by 3 degress. One degree of angle with an antennae height of 3m equals a 5cm jump in position.
I found Dual didn’t experience these spikes in roll and was much more stable.

Over smooth or slightly bumpy round there was very little difference between Single and Dual, both performed very well and had stable Roll and low XTE values.

Dual was much better doing U Turns and curved boundaries keeping close to the plotted line.

Another positive for dual is the heading at slow speeds is much more stable and the tractor always knows which way its travelling, no need ever to have to reset the direction on screen.

After an hour of testing Single and Dual driving the same AB line, I was able to maintain a lower XTE value more consistently with Dual, both where very good, with Dual I very rarely had an XTE over 2cm (less than half an inch), with single saw a few 3,4 and 5cm XTEs on screen, this maybe to do with settings.

With Dual it doesn’t matter what angle the PCB is orientated, for testing I had it floating about behind the seat.

In conclusion Single and Dual both perform very well, Dual will cost £2-300 more than Single but was more stable on rough ground, better at slow speeds and a more stable heading.

[Daryl]

Teddy, thanks for posting your experience. I had agopengps on a claas arion 430 with solid mount cab, IMU and F9p connected to a nano (panda) and it was great. Anyways, I’m considering a Claas 620C and it has cabin suspension. I have been considering if the duel gps would be worth the extra cash, you have confirmed that it is in your experience. I’m wondering if your claas has cabin suspension and does the suspension impact accuracy on the ground noticebly?

[TeddyStamford]

Hi Daryl, I have cab and front suspension, obviously the cab rocks about, but doesn’t seem to have any effect on accuracy, drives really straight and smooth…

AgOpenGPS Dual antennae

[Daryl]

That’s great, thanks. Now I just have to decide if I use a Keya wheel or hydraulic.

[TeddyStamford]

Reading old threads about Dual antennae, there has been a suggestion that as the vertical accuracy of the F9Ps is not as good as horizontal, the roll value could be wrong by as much as 2 degrees or more which would give ground position shifts in excess of 10cm.

Having used Dual extensively now, this is not something I’ve found in practice.

As way if a little experiment parked on sloping ground today and left the tractor parked, but left AOG running and thought I would see how stable or not the roll value was.

Measured the roll angle with a digital meter…

Then checked the roll periodically, you can see the time on screen…

The roll does flutter up and down 0.1 degrees, but always centred around 5.1.

[TeddyStamford]

One cited downside of Dual is it may not be as reliable when close to trees.

I’ve several miles of field boundary adjacent to large Woodlands/Forest.

I’ve been drilling/seeding in one field with a 1 mile (1.6km) boundary against the woodland.

Happy to report Dual performed faultlessly, didn’t miss a beat, autosteer the whole boundary curve under the tree canopy in places, no problems at all.

[WestMIguy]

Thank you for posting your experience with dual antenna gps. I was on the fence about running a dual antenna setup, but then I ordered the parts after reading your first post about your experience. I was able to work in the field for the first time today and it worked great. Single/ IMU does a good job, but dual takes it to the next level. There is a noticeable improvement in performance.

IMG 7149

[TeddyStamford]

Almost 6 months later, really happy with how stable the Dual performs, just totally reliable.

Performs really well at higher speeds and over rough ground and even steers well in reverse at speed.

AgOpenGPS Dual Antennae

[WestMIguy]

AgopenGps dual antenna RTK drilling wheat

Here is a video I took last week drilling wheat. If anyone is on the fence about a dual antenna set up you should try it. My average cross track error
is now measured in 10’s of an inch. The tractor runs like it’s on rails.

[del_boy]

Very smooth set up. Is that with the f9p or the um982

[WestMIguy]

Thanks, this is running dual f9p’s.

[Bullhill]

I have 2 tractors with AOG installed, one with single antenna + IMU and one with dual antenna.
Can fully agree that the one with dual antenna follows the line better and the benefit with not worry about mounting direction of PCB did make the installation easer.
Another ting is that the tractor always know what’s forward and there is no need to touch the tractor on the screen to set driving direction.

[dave456]

Question, my brain says that the antenna’s would work better down the centre line of the tractor.

Reason one, moving away from the rear axil has advantages, the amount of movement seen as the measured point is further from the tractors natural pivot point the rear axil or implement so movement away from the line is easier to see.
A bit of research on this topic to read.
https://www.mdpi.com/1424-8220/11/6/5630/htm

Bigger shifts can be easier to see through the noise.

Next having them in line down the centre line reduces centre of moment differential. If they are the same height and on the same centre line the number of possible factors in play are reduced and no offset differential to measure.

Ok final question, most tablets can use GPS can you use the tablets GPS as a second RTK location?
Can the tablet see and use an RTK correction signal and become a second antenna RTK location for all systems without a second antenna being needed?

[Uprishaa]

Has anyone tried dual antenna setup and single antenna setup on the same vehicle with cab suspension and figured whats better?

[davidroberts30]

@TeddyStamford has i think

[Uprishaa]

Hope he will respond
What would you choose?

[del_boy]

I believe @TeddyStamford is firmly in the dual camp.
Over on the telegram is certainly mixed reviews.
What system have you currently got? F9p or um982?
The more expensive imu is getting a thumbs up

[Uprishaa]

F9p, and imu from ardusimples adafruit bno085

I got 2 antennas ready but not sure if its going to work. I got 5 agopen tractors working for 2/3 years now and none of them had cab suspension. Just dont know whats the best way to deal with it

[TeddyStamford]

Yes I have cab suspension, I used single F9P and BNO085 for two years, was quite happy.
I fitted Dual antennas and PCB but kept a single system on the tractor for a few days for testing.
On smooth ground there wasn’t much difference, both steered well.

But bumpy ground, curves and U Turns Dual is significantly better.

I wouldn’t hesitate to fit Dual again.

[Uprishaa]

Thanks for your feedback!