Seeding and hoeing on slopes

Projects Project ideas - in progress
21

The fact that the tractor would remain pointing forwards even when reversing and the fact that you can fluently activate auto-steer when going forwards and then changing to driving backwards, sound like very attractive behaviour if it comes with the dual antenna approach.

I find AOG behaving very well with a single antenna (+brick + DOG2) when working normally, driving forwards but could consider dual antenna only for the two advantages mentioned above.

A pity AOG cannot achieve this with a single antenna. It is possible as our two commercial tools do it but perhaps it is too difficult to detect a sudden change from forward to reverse after a momentary zero speed and then glue the heading accordingly instead of rotating it 180 degrees. I assume this is very complicated to implement and/or comes with other disadvantages and leaves me happy to accept AOG as it is. Dual antenna always being a “not so expensive” solution. EDIT: I guess should have said “not so cheap” solution, single antenna always being the lowest cost option.

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22

Maybe AOG could take another input from the tractor for reverse in this case and thus knowing when it is shifted in revorse or if not going forward?

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23

Was thinking last night, my issue with it not following the line in drift / slope conditions, cant be that its following the stanley point out in front, as if it was, the off line error would be 0 right? but its not, the error at top center cant be 40-50cm from 0 as you follow a slope…tractor at angle to line obviously…but it wont correct it…

24

I wonder what the BNO055 IMU is good for as apparently it doesn’t have the two dual antenna advantages mentioned by @darrenjlobb (keep pointing forward when reversing and staying on the line in reverse)?

Since the BNO055 senses magnetic field strength, I thought it would also act as a heading detector. With BNO055 saying “tractor points north” and moving direction being south, AOG would know that we’re reversing. So shouldn’t the tractor also keep pointing forward in AOG and stay on the line?

(I’m aware that the magnetic field strength sensing is subject to disturbance and not as reliable as the two antenna setup. But I’m trying to avoid the two antenna setup for now since I read about the hard time people are having setting this up/getting it to work on the sidehill.)

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25

The sidehill issue isnt a dual antenna issue…its the same with single antenna, it depends where in the world you are / what tasks you perform…the vast majority of people dont seem to have much of a problem, but here in the UK, I think most people are finding its a problem. But I dont think the dual antenna makes it any worse… @Alan.Webb is running a single antenna (F9P) setup here in the UK also, and finding the same problem I believe…

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26

Good to know. I’m glad you guys have similar field topography there. Thanks for sharing your experience!

27

As bit of an update,

Not had chance to go out with an implement yet, but did some quick testing today on a steep sidehill with just the tractor, enough to cause the tractor to drive off track on its own…

So initially with previous settings (roll set to none, as roll calc on position is in done dual ESP), the tractor would drive 25-30cm off line going upwards along the slope, and would drive near enough dead on the line going down over…obviously its harder for it to “pull” the front of the tractor up the slope, than it is down going the other way.

I then enabled Roll from OGI, which is working, in that, I am now getting a live roll reading in AOG, which looks to be correct and nice and smooth… I then tried applying some sidehill draft gain… initially set to 5, but immediately realised this is far to much, as this pulled the tractor 30-40cm high side of the line going the more problematic direction! So dropped it down and have ended up with around 2…

The problem now though, is going that way, with just the tractor, It does sit close to the line…however going the other way (slightly downward slope) it then sits considerably ABOVE the line, as the extra gain is to much… I also think that despite this 2 setting being ideal going one way right now, the second I put an implement on / introduce more load / drift, it would instantly be wrong / need more… It seems this setting being a static setting is a bit flawed…

@BrianTee_Admin if you have the time at some point, can you explain the reason why AOG wont always try to meet 0 error ? IE when driving 30-40cm off the line, at an angle on a sidehill, why does it not request more steering angle to meet 0? Its like it hits a limit and thats that…More understanding of this might help figure out what we can do to help it…as it needs to always try to meet that target by itself, that way it dosnt matter how steep the hill, how much drag from the implement, if error >1, it always needs to keep trying to correct by adding steering angle, right?

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28

Because it doesn’t have an integral term :frowning:

That said, i haven’t experienced the kind of error anywhere near what you are experiencing.

Dual antenna heading is very different then single antenna reading when the tractor is sliding a bit sideways down a sidehill. The dual antenna will show the actual direction the tractor is pointing, not the direction it is traveling. A single antenna will take 2 consecutive points and from that will show a heading no matter what angle the tractor is drafting. The imu the same way.

But the dual, all it knows is what direction it is pointing, not actually traveling.

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29

Yes this is true with regard to heading…Does that actually effect the calculation though? Or is that just done on position? I think possibly alot of people, don’t see this issue as they simply dont have the hills that we do possible? or at least dont work on the side of them, esp with 3 point implements…

How hard would it be to add an integral term to the steering calculation for stanley @BrianTee_Admin ? I would love to be able to try this…

In terms of keeping on line / keeping implement where it needs to be, in my head, having true heading from dual antenna, is technically a good thing right? As if it knows the true angle, and position, and all your implements sizes / offsets are set correctly, it literally knows exactly where the center of your implement is right?

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30

I don’t know if technically it is a good thing, while it is steady, it doesn’t actually reflect the actual heading of the tractor on a sidehill, especially with heavy equipment behind. It may be why you are having the problem holding the line on a sidehill, whereas a single antenna/imu displays exactly what the heading actually is.

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Maybe I need to try hooking up an IMU just as a comparison on a sidehill… If IMU is still the answer for true directional heading…I would still say there is potential good use of dual heading for keeping the implement on the line at any tractor angle…provided fixed implement anyway…

What is the most recommended IMU at the moment, or maybe with RTK I might be just better off with a fix-fix heading…

32

I hope to get my Tinkerforge IMU Brick 2.0 soon. Once everything works I’ll definitely test the setup on a sidehill and let you know how it behaves

33

Maybe if we could include pitch in the calculation, so when going uphil positive pitch adds to the roll gain. and downhil reduces roll gain.

Or maybe even use the mma on pcb as pitch. I assume you do not use it now, so place it (or change axis) so the roll is showing pitch instead, and when combined with the roll from Dual GPS it would add or reduce actual roll when going up/downhill ?

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34

I personally think the issue is, at least in part, the reliance on heading. Parallel errors such as this appear for a number of reasons. WAS inaccuracies, sidehill draft, compass drift and side load. They all cause the same basic effect and code to spot the situation could combat it. I’m trying to come up with a sort of fix using the arduino code. Hopefully testing it this weekend.

Probably would be better in the main code but I can’t make head nor tail of where to find the steering set point calculation. Not helped by me finding OO programming very difficult to follow.

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35

Purely out of interest, have you changed from Stanley to PP on the go whilst actually experiencing this effect? If so, what was the result?

36

Watched your video about the error and integral term, good information. Got me thinking on the error, wobble, you turn etc. Just a thought, what about an aggressive error return value. There is sort of this in the Pure Pursuit. If driving straight, look ahead is out there a ways. in the you-turn, it is a percent of the value. Now, this could all be set internally based on the slope of the line that the equipment is following. If the angle is straight, then maybe not so aggressive. If detecting a sharp curve or you-turn, be aggressive and try to overshoot it. Always wished I had a control on the car that allowed me to determine how aggressive the cruise control tried to hold a certain speed. Some days, yes shift down three gears and try to hold 80. But, there are those days where 70 is still ok. Some days we farm with precision, some days we relax. In other words, let the crop control the aggressiveness of the steering. Rolling beans might not be as critical as planting them. But when it is time to turn, it’s time to turn. Just thoughts. Keep up the good work.

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37

Its really tricky with steering being a second order derivative - as you approach the line you steer away from it. “Adding” a bit of steer angle should resolve the not getting to the line, but instead it just crosses over it and repeats the problem back over the other way. Pretty frustrating.

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38

Yes. I understand. I don’t think altering steer directly is the answer to this issue, rather altering the environment in which steer runs. ie, the parameters by which it operates. Leaving steer to operate as it does but compensating for additional external forces by cancelling them out.

…if any of that makes sense :grimacing:

That’s how I’m trying to attack it in the Arduino code anyway.

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39

I think that the problem we are talking about here is also affected by the location of the antenna. Under the influence of lateral force when the tractor is pulled sideways, to maintain the track it must travel at a certain angle characteristic of a specific balance of forces. Locating the antenna in the middle of the tractor, the rear axle can then move next to the track despite the antenna being perfectly on the track.
In my opinion, you need to place the antenna over the rear axle which is the actual pivot point of the tractor and it is the rear axle that should be the base point.

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40

There’s a post by @Aortner regarding antenna placement: Antenna placement

“Brian Tee, [07.11.19 01:36]
Stanley guidance uses heading to calculate the distance the steerer wheels are offline, so putting the antenna over the pivot with a stable heading from imu is as good as Pure Pursuit and antenna above the front wheels. It’s a complex interaction”

As far as I understand we can place the antenna right over the pivot if we use heading from IMU. Think I’ll do it this way