For clarification, I was answering your above post.
@ESCBB from the hardware point of view you are able to do the Cerea solution with the AgOpenGPS PCB: there is an input for a motor turn sensor where you can connect the HKT22 sensor (mind, that the supply is 5V). Furthermore, when using a IBT-2 motor driver, you don’t have additional forces, because that driver has an extra “disable” input, so that the DC motor can turn freely. So from the HW point of view, all is there.
But: The software concept is different, but I never digged into the details there. That’s a bigger discussion still ongoing that I don’t want to repeat. Maybe one day a clever software guy comes up with a solution, maybe with two RTK antennas… Let’s see…
Thanks for your answer. About the IBT-2, I have just ordered to test it, but I dont see how to manage the “disable option” so to avoid the extra force. Could you help on this?.
About the need for WAS like ER10031, while AOG is being now under a hardware redesign process to reach perfection (per the discussions on Telegram forum), the part of the system to get wheels position reading seems forgotten. I say this because the use of ER10031 or similar, which are not ruggedized, nor designed specifically for the use that AOG is doing (mud, dust, water etc).
For the users with electrical motor (not valves), a solution with HKT22 together with the Phidgets controller 1065_1B, solves the problem, and is an affordable cost solution.
I hope one day the software gurus see the path already walked by Cerea.
Regarding the cut off possibility:
In steer.png file found in the support folder, you see Led_pin or Aux hydraulic relay, that is the one you use for your relay to cut power to motor driver. Works both for cytron and IBT_2 just different pin from PCB
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Thanks Larsvest, I see now the steer.png file, but not what I must change. What I understand is that these two “Led_pin Aux hydraulic relay” allows to feed a relay, but not see how are interfacing with Cytron and what needs to be changes from what I have now. Perhaps is very obvious and I am still sleep.
I knew it was there, just hard to search for the right words 
This word combi in search got me there! relay led_pin
Click on Fendt and you see a sketch with motor, relay and motordriver.
I see now, many thanks.
From the steer.png image, I see 2 “Led Pin…”, one in clear blue from the “Dir” in PCB, and the other one in dark blue from the “PWM2” in PCB.
The sketch you refer, is edited asking: on PWM2 (Pin 9 on Arduino)?.
I wonder which of them.
I understand this activates an Arduino relay board optoisolated, as recommended on the next post from the Fendt.
A lot of things to test for the next weekend. 
That is to be found in autosteerschematic.pdf (also in support). Follow line from arduino D9 - it goes to PWM2 on pcb (can also be found on pictures of pcbV2 but not easily. It passes R14 on the way
Reason to 2 different options is IBT_2 and Cytron motordriver, they get different pin setup of arduino (which today is done in AGOpen program) before version 4.1 , pinnr. setup was done directly in the ino program/setup of autosteer.ino : And that is why today the ino name is Autosteer_USB_4.3.10
But as GoRoNb posted above you don´t need relay with IBT_2
@ESCBB from the hardware point of view you are able to do the Cerea solution with the AgOpenGPS PCB: there is an input for a motor turn sensor where you can connect the HKT22 sensor (mind, that the supply is 5V). Furthermore, when using a IBT-2 motor driver, you don’t have additional forces, because that driver has an extra “disable” input, so that the DC motor can turn freely. So from the HW point of view, all is there.But: The software concept is different, but I never digged into the details there. That’s a bigger discussion still ongoing that I don’t want to repeat. Maybe one day a clever software guy comes up with a solution, maybe with two RTK antennas… Let’s see…
@ESCBB There is a nice TI paper. Fig. 5 shows the current flow: left: motor driven actively, middle: what the IBT-2 is doing during idle (you still charge the battery when turning the steering wheel fast enough), right: what the Cytron is doing (motor short = highest breaking force). If you simply put in a switch to to motor lines, the breaking forces are minimized. That’s the best option apart from disengaging the motor mechanically.
Nothing better than the image, I got it.
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Regarding the original question. Given we have gps speed and an IMU that outputs angular velocity, it should be possible to have a stab at wheel angle calculation shouldn’t it?
I’m presently attempting to port the standard arduino code to an ESP32 , so I’ll try to have a stab at something on that if I manage it.
It will have the added advantage of becoming much more sensitive with speed, which could be useful.
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Does this work fine?
The problem was, that a inductive proximity switch is not exact enough for detecting the 0° position. I’ve a hall effect sensor on my desk. Seems to work fine, but the weather is not like testing outside right now… 
I’ll keep you tuned!
Honestly no progress here, because in the meantime I’m using the build-in WAS of the two tractors, I’m working with. But there is a proof-of-concept made by Greg from Farmtec now: John Deere 3550 RTK Farmtek Sans Capteur de Braquage - YouTube. My ideas seem to work in the real world 
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Can you get the source code as per the license agreement?
I may complain, that my idea has been stolen, but I won’t. There’s no use in acting like a prima donna. GPL3 has clear rules, and we all live in states of law fortunately.
The point is, that a lot of people like to tell, why something is not a good idea. To me, it became clear in the meantime, that this option will work but only, if the rotary encoder would be combined with the RTK data - no job for a small µC. But even in case someone skilled in C# (I’m not) wanted to try, AOG was closed-source in the meantime, so that there was no chance to contribute apart from a few.
EDIT: nevermind. Posted again when I shouldn’t!
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As we can see, he really copied my whole story. Apart from the extremly uncooperative and most likely illegal (related to AOG) behavior, it’s a nice idea to have this or a similar kind of self-learning function in the public trunc of AOG as well. At least in the German Telegram group, nearly every newbie is asking how to set up all the steering parameters in the beginning. And then, everybody tells his gut feeling…
And of course a good chance to turn the table…
The teaching may detect the following parameters:
- turn radius/max. angle left/right
- breakaway torque/min PWM for the steering wheel motor (may differ left/right)
- max. delta WA/delta time
- step response of the steering system (mathematical basis for a good steering control)
I can offer to contribute to the community adding the steering wheel angle sensor to the Nano code as my PCBA is fully supporting the use of that sensor + WAS or CAN. And doing some testing of course.
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If it helps, I could describe the calibration procedure of an old autofarm GPS system.
They measure at least
wheel angle position min/max/direction,
min Max pwm for the valve