I want to use pixhawk with the apm rover firmware to operate an agricultural tractor. I need to set up my tractor as an rc vehicle.  My plan is as follows: any feedback I can get is appreciated.  I plan to order the parts in the next couple days but if there is something I've overlooked or my plan has no chance of success let me know.

Throttle control: Linear servo (https://www.servocity.com/html/25_lbs__thrust_linear_actuator.html#...) I don't see too many problems here.

GPS: I plan to use the gps already installed in the tractor.  I am planning on buying a pololu 23201a to convert the serial nmea to something I can input to the pixhawk.

Steering: This is what I'm most worried about.  The tractor has an electric over hydraulic steering valve, so basically provide 12v to right side tractor turns right, provide 12v to left side tractor turns left. I am planning to put in a dual 12v relay controlled by pwm signals for the steering https://www.servocity.com/html/electronic_pwm_controlled_dual.html#...  Anybody have a gut feel on whether this will work or not?  The problem is the steering output from pixhawk needs to reach a certain threshold before steering valve will operate this is quite a bit differnt than how it is set up on my rc car where each pwm value corresponds to a specific steering angle.

Clutch: Much testing has to be done with a person in the cab to operate the clutch and some sort of ignition failsafe installed before I get the tractor to be totally autonomous but I would like to start thinking about the clutch, and start testing some setups with a person in the cab.  I could get a linear actuator that releases the clutch when throttle pwm reaches some predefined threshold? But I would really like a system that if the power is cut or signal is lost clutch is automatically depressed which will stop the vehicle. I could set the clutch up to be always depressed and use a linear actuator to engage it. Connect the actuator to the clutch with an electric solenoid so if power is lost actuator releases and clutch disengages. Anyone else have some good ideas?

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Getting ready for harvest out here in Alberta, really would like to help work on this project, and add this to our own operation out here.

I have a heavy background in programming but have been out of it for a few years, but have started to work with quads and APM for last couple years.

Just have to get the harvest out of the way, but I'll be checking in and seeing how things go for you.

BTW, totally understand the mindset of the group you had out, there will be pushback around here, but there's still been a lot of interest in this when we've discussed it.

That would be great! The more farmers that can develop this the more progress we will all make! We will have to see how many people are interested and after we are all done harvest we will have something cool to work on over the winter.

Dear Matthew,

If it is okay for you and everyone else I can update my electrical connection schematic (pdf) when I get information from your setup. Everyone can use it to make their application.

Best regards,

I'm passed the halfway mark now.  My hired man and my Dad even started it up on their own the other day. Had to call me for tech support when the app kept freezing.  It turned out to be the combine gps not getting a lock.  They hung in there with me till we figured it out.  It's too useful to be giving up right away and putting a person back in it.  I was worried something had gone really wrong the other day when the light on pixhawk wouldn't go blue and then green it was just solid white.  Turned out to be a full sd card. Its being run for 10hrs or more most days so I guess that's not a shocker. 

Matthew, Congratulation, great work!.
I was just thinking to do something like this when i read your post! i have spend my little spare time reading the last few days.
I was planing to start just steering wheel of my old tractor ( Fiat 900 tractor). For that, i was thinking to put a rotary actuator on the steering wheel drived by a brushed bidirectional Esc.
Thanks to your post, i will change this, and i´m now thinking add a potentiometer to feed back, i´m thinking in a arduino board between the pixhawk and the driver, the board will compare the potentiometer with the "position PWM" from the pixhawk, and send a "speed PWM" to the rotary actuator.

What do you think?
Also i was thinkin in a RTK with a Raspberry

But, step by step.
I´m from Argentina, and like Cala mention, it not easy for us.
I have to work just with the few things i have on hand, any purchase it take a long time to deliver and very expensive

I think you are on the right track.  I don't know if you can get this https://www.pololu.com/product/1393 it's the same control board i used between the pixhawk and my hydraulic valve for steering.  It should work equally well for your application.  You wouldn't need the arduino or the hobbywing product so the cost when it is all done might be comparable.  It has a spot for feedback and it's own software and a really slick interface for visualizing the signals so you can do PID tuning on the pixhawk to get the output in a range and speed that you like and then you can do PID tuning on the JRK to get your rotary actuator to steer smoothly.  It seemed to me the actuator you picked is maybe too big and fast there might be a cheaper option but I'm not sure where I would start looking. I think you know this but the potentiometer needs to measure the steering angle of the tractor wheels not the steering wheel position.

What is the purpose of your project?  Just steer the tractor up and down the field in straight lines or turn the corners at the end too?  What are you planning to use to interface with the pixhawk once you get it on your tractor a phone, tablet, laptop?

Matthew, i saw the jrk, i still thinking in the hobbywing esc+arduino (arduino nano for example) because it is cheaper.
I have a arduino compatible board already which i have just started to program to read an ultrasonic sensor HC-SR04 (kk multicopter v5,5 ). i will use it to get an analog out and put it to the pixhawk. sow, i can use the arduino for more than 1 task.
the rotary actuator is still to be determined, just looking for.
the potentiometer, i planing to put it in the arm joint who drive the wheel

I was planning to start with mission planner on my notebook, or tower on a tablet, and use the tractor to seed (ideally) with a mission similar to the survey which have already using in my quadcopter. just need to configure a new camera with a horizontal field of view similar to the plow


I think your plan is solid and it should work good.  The hardest part is probably going to be mounting the potentiometer, you have to get it centered over the pivot point so you don't torque it in the wrong direction.

yes, it should be my fort, i´m not a programer, not a farmer (have the tractor and the field but not farmer) i´m Mechanical-aeronautical engineer, so, i will probably make an assemble very similar to the one you have done jajaj.
i don´t have to much time and the field is far away from my home (100miles), an i just go there on week end so, i will improvise the potentiometer mount in the moment jaja.
i still have to define all the component needed to make the purchase and wait.
Thanks to reply, i will follow your progress. i hope get my things ASAP to start the test

Same challenges in Brazil, Carlos... Huge delays and import duties for any product. 

Probably you are already aware  but there was an effort of EMLID to create low-cost RTK GPS. THe name is Reach and they already have a autopilot based on RPI https://www.youtube.com/watch?v=cqmtBR--Ja0 .

Reach uses RTKlib and tallysman antennas - a great starting point to understanding how it all works. There is a whole world on how improve positioning systems with many not so costly solutions. 

Good luck and I hope to see Christina Kircher out as soon as possible

YESSSSS!!!!!! God listen you Gustavo pleaseeee!!!!

I'm thinking about surveys too (....but only trying to survive :( now) it's looks interesting form many task at the farm, I follow your advances for the moment and one day I hope to return experiences to you :) many thank's to share them. 


Great work, great job and huge accomplishments!!!  Read all 14 pages of posts!

Here in Northern California and lots of rice growers, still.  Need to find a progressive grower or two, and begin a project using Navio+ and the new RTK Reach product.



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