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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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.
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.
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?
Yes if you go to here http://www.outbackguidance.com/Store/tabid/388/ProductID/301/Defaul....
Then select the "kit only" you will get the hydraulic valve and all the hoses and brackets needed to hook it up as well as the wires that connect to the valve. Don't worry about which gps you say you are connecting it to b/c you will be cutting the wires anyway. I just went through this for my tractor model and it came out to $1290USD I am sure I got it cheaper from my dealer but that is the cost on the website.
Then you will need this https://www.pololu.com/product/1393 to put inbetween the pixhawk and the hydraulic valve. You might get away with the 21v3 but I got the big one to be safe. This is a really nice board because it allows you to hook up a wheel angle sensor so the wheels behave just like they would if they were turned by a giant servo. If you don't have a wheel angle sensor on your tractor you can add one, any potentiometer will do or you might be able to get a kit from agleader http://www.agleader.com/.
Can you describe what is involved in installing the Outback kit a bit? The quote I received from a Texas dealer was $7500. (e.g. Am I replacing any existing power steering components or only adding components?) Am I basically adding a hydraulic control valve between the current steering and the steering pistons and then connecting an electronic control unit to the hydraulic control? The pdf online is pretty vague.
First the dealer said, "The 5055 is a very small tractor it might can be done, but I would have to do some research since the tractor is not on the model matrix. This tractor may lend itself better to the EDrive Esi electric steering wheel versus the hydraulic steering option....".
After answering a few questions (e.g. that a JD5055 has open center hydraulics) he came back and said it would be $7500.
You don't replace anything. Basically just adding some hoses and a metal block that has some electric solenoids inside. One opens and the tractor steers right other opens and tractor steers left. $7500 is a lot. He must have quoted you for an entire autosteer system including gps reciever, monitor in cab and edrive box. Everytime I've done it my tractor or sprayer has been on the list and has always come with really nice instructions (including pictures) that show you which hoses and fittings to replace. If your tractor is not on the list then you might need some custom fittings for some hose ends. Since it is smaller than most tractors the hoses should all be long enough if you order the kit for the closest model to yours. I would phone outback direct I have had great tech support from them in the past.
I have an EDrive VSI (electric steering wheel) in my swather and it works good. I have not tried to control it with the pixhawk but it should be possible. This would require a good amount of disassembly on your part.
Hi Matthew, Slowly digesting your work and wishing I had more time but I may soon get my wish as the weather is starting to sour in MN. Tillage is done for the year! Need to pull the MX305 in the shop some day and crack into the console. The controls are similar to your Deere although the MX is power shift while I suspect your Deere is IVT/CVT? Will look the model up to verify. For those interested I went down the rabbit hole on Agleader's site and found an interesting article on Wheel Angle Sensors. Also the p/n for said kit is #200-0015-01 but I think there's another number that may be more relevant for a users particular equipment. This looks like the basic encoder, mounting bracket, and a few other goodies. IDK what the cost is yet. Here's the link to the wheel angle sensor article.
http://www.agleader.com/blog/explanation-of-wheel-angle-sensors-and...
Matthew, what did you end up using for a wheel angle sensor? Perhaps you tapped into whatever was already on your Deere?
Jim
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