AgOpenGPS and a small vehicle/lawn tractor - The Combine Forum
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post #1 of 5 (permalink) Old 05-04-2019, 09:19 PM Thread Starter
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AgOpenGPS and a small vehicle/lawn tractor

Hi all!

I'm new to this forum and AgOpenGPS. AOG Looks like a really interesting project with a bright future.

I've been running simulations for my small lawn (mower) tractor and I've run into some problems.

Currently there's no option for tool between wheel axles. There is a workaround, I expect: set the tool behind, rigid, reduce hitch, tow-between and trailing to minimum allowed.
In theory this should work. Tractor is small enough that tool 20cm after vs tool 40cm before rear axle shouldn't make a huge difference. However, I can't confirm at the moment, at least not for my tractor. See next issue.

As soon as I reduce the wheelbase, turning goes bonkers. I.e. it doesn't work properly, if at all. I think the math/algorithms break for such a small tractor.

Here are my tractor parameters (actual, physical, measured):
- wheelbase 120cm
- max steer angle about 45deg
- wheel to wheel width (left outside to right outside of the wheel, front and back the same) 88cm
- tool width 92cm, one section
- min turn radius 70cm (rear wheel outside to same spot when tractor is 180deg turned is ~135cm, rounded up to 140cm)

If I keep wheelbase at 200-250 or more and turn radius near those values, then turning might work (hit and miss) depending on exact numbers used. If I set those values to be lower, then turning does crazy things like in the screenshot, or even far worse. Interestingly, reducing the turn radius even with wheelbase 200-250 causes simulator turn radius to increase.

In my sreenshot first two turns were with min turn radius set to 200, last two turns were with turn radius set to 100. Wheelbase was 250 on all turns. Section was set to 1x90cm. All else was at default values.

I tried tweaking autosteer options as well, it didn't make any significant difference. Low wheelbase value seems to be the key value that causes turning to go haywire.

Am I missing some settings? Anyone else experienced the same or similar?

I'm running AOG_dev commit f72b84e (3 days old) on linux under wine. Some visual artefacts are there, but my environment shouldn't affect maths and algorithms.

I'll be happy to make some recordings or capture more screenshots if needed.



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Last edited by ViktorI; 05-05-2019 at 01:02 AM.
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post #2 of 5 (permalink) Old 05-04-2019, 09:55 PM
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1. Yes you can. The width isn't used because AOG is based on the bicycle model. See pic below with appropriate settings.

Welcome to the forum, there are a few others working on mowers as well. Contour I believe is the only thing that doesn't work for really narrow implements. Settings will be quite sensitive of course and must be dead on. Is your antenna over the front wheels - or even sticking out ahead of them? You need some off track distance for sure.

Putting the antenna over the back pivot axle would not be good. Also, is your steer wheel angle sensor reading correct? When the wheels are at 45 degrees, does it say it is at 45 degrees?

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post #3 of 5 (permalink) Old 05-05-2019, 12:55 AM Thread Starter
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Here is a quick video demonstration of the steering/turning issue that I'm seeing.

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post #4 of 5 (permalink) Old 05-06-2019, 07:21 AM Thread Starter
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Thanks for the quick reply and thanks for the welcome.

To clarify, I'm running this in simulator only. I'm still on simulator before I start implementing in physical world. Did I neglect to tweak more settings and that throws off the simulated environment?

I've reloaded the same field, default vehicle + tool 1x90cm. Then adjusted settings. So "Tool is Ahead" is actually measured from the pivot axle? Very cool.

I've attached a screenshots with settings and results. Notice that sim-tractor turned left... without going slightly right. It did not respect the dubins sequence of first go right then wide left circle as wanted. Same happens with min radius 900. When I started the turn it oscillated between left and right sequence of yellow dots and decided to latch on to left instead of the right sequence, and eventually the steer went haywire. You can see that in the video above.

Cool about the bicycle model. I thought as much. That's why the software doesn't need the vehicle width values.

Did you try the simulation with just those settings? Turning doesn't properly work for me with 100% repeatability. I expect I either need to tweak more settings to make simulator work or there's a bug. Do you want me to record some videos?

I was the one who brought up the idea of implementing a "fault server" back on youtube two days ago. That idea is basically abstracting software layers. I have background in software enginerding. Abstracting is good when used properly. Helps out when you deal with complex systems.
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post #5 of 5 (permalink) Old 05-06-2019, 07:24 AM Thread Starter
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Screenshot of settings and results they give me.
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