Apm Rover in tractor setup.

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#.VVOUCJNyP5U) 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#.VVTFmZNyP5U  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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  • Hey everyone,  I found a more generic kit p/n and the instructions for mounting.  Once again, this is the AgLeader solution.  The generic kit p/n is 200-0625-01.  Here's a link to the installation instructions from AgLeader's dealer site.  Hope everyone can see it...


    As Matthew indicated, I suspect the Case Magnum MX305 (and others) that are auto steer ready will already have a sensor that can be hacked into.  This should be useful for users who wish to do a tractor that is not auto steer ready.


    • Jim, The generic ag leader kit you have referenced ( 200-0625-01 )has been replaced with PN: 4100175-01 which includes the following pieces:


      If you wanted to save some money, you can get just PN 200-0468-01 by itself which includes the sensor, threaded rods, and joints.

      This wheel angle sensor that Ag Leader uses has been used in many different vehicle applications and is very common. The only difference between different vehicle kits are mounting plate brackets for various machines. The sensor itself is the same. The generic threaded rods are the same between kits. The rods come in a large lengths and the user is asked to cut the rods to their specific machine requirements. 

      Ag Leader (and also AutoFarm) has used this particular sensor in many many vehicle applications for many years. If you are ok with used sensors, I would suggest visiting with one of your local dealers and asking if they have any used wheel angle sensors available. As people trade tractors and switch guidance systems, often these kits are pulled off and thrown in a box as spare parts.

      Ag Leader is also very good about posting vehicle install manuals for their steering kits for free on their website If you need ideas for your specific vehicle ( installing aftermarket hydraulic valve, installing wheel angle sensor, location of factory steering valve, etc). Go to the bottom of this page for a list of vehicle install manuals (blue links under 'Kit Install'): 


    • For those interested I just received my Wheel Angle Sensor Kit part no. 200-0625-01.  No time yet to install, but wanted to share photos of what came in the package.  Cost including shipping (in Texas) was $531.

      Be aware there is no wiring harness included.  If you can open the MS One Drive link attached you will see the photos and notes  and some research I did as I am thinking I will have to craft my own mating connection.

      One Drive link to notes

      Wheel Angle Sensor Kit.docx
      Microsoft Word Document
    • Photo of the installation.  Brackets were made a fabrication shop nearby.  Cost $300.  I made the wiring harness with the parts from Mouser mentioned above, but I did not have it on when I took this photo.  The arc of travel is about 2500 ticks vs. the full 4095, but should be plenty for me.


    • Thanks for sharing Al. Looks great!
    • Developer
      Really nice!
  • Ok so I got rid of the actuators in the cab.  The controls now run through arduinos which normally pass the signals through so you can jump in the tractor and use it like normal. Or at the flick of a switch the arduinos will do whatever the pixhawk is asking for.  Here's a video that goes over some of the details.  The code for the arduinos is on github for whoever is interested.

    • Does this mean you trusted the redundant Arduino Mini with the DACs over your brake pedal actuator? So it's gone? It seems like it would still be worth having that failsafe in place.
    • The brake is still in place at the moment but I'm hoping to not need it. Now when the safety system is tripped the arduino for the speed control slows the tractor down as much as possible and a different arduino puts the transmission into "power neutral" which is like Park but not so abrupt that it tears the tractor apart. I've also confirmed that a failure of one or both of the arduinos throws error codes that stop the tractor. I need spend some more time testing before I remove the brake though, but I'm hoping to get there as it is in the way a bit when we drive the tractor manually.
    • I think the definition of bravery comes to mind when I think about you "hacking" a $100K tractor.  Good for you.

      In a previous post you mentioned, "...You can get the valve and all the hoses and fittings from outback guidance for $1000....".  Can you add some details about your steering solution?  I'm looking at the Outback website and the Outback eDriveTC is coming in at $3K plus, but I'm guessing that is the whole autosteer solution.  What are the minimal Outback components that you had to add to your JD tractor to get a signal you feed into the Pixhawk?

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