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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:o :o Impressive, next step tractor doing "follow me" to the combine.
Thank's to post your great experience.
Thanks Cala. Are you a farmer? We need as many farmers as possible to start fiddling around with this. We will make more progress together!
Yess! I'm a farmer too and I was thinking about what happens with Pix in a tractor, now I have the answer, it's AMAIZING!!! :o I'm flying copters and planes for agriculture purposes, I try not to read about Rovers to avoid be enthusiastic about Rovers for the moment but first I saw a lovely sixs wheels rover that crosses everything and now this impressive proyect, impossible to avoid, I think that this tool in combination with an RTK like Pisky are going to give us a very usefull cheap tool, today in my country (Argentine) is very expensive to have an automatic pilot with RTK.
I have the idea to begin with a small rover to learn about them; then I think that it's possible to scale a bigger one to spread bait and them try with a tractor, but this year looks impossible to start new proyects here, farmers are living one of the worse years, many of us are going to dissapear if there no exist a drastic change in goverment politics, the 82% of our income is going to the taxes and cereal prices are on the floor :( (We have presidential elections this year) .
As soon as I can do something in this way I'm going to share here for shure.
Thank's Matthew, I follow your progress and share if I find interesting information for this proyect.
Yess, I'm thinking that telemetry can be usefull too :D Eg with a high antenna we can follow machinery from the office ;) ....
Great Job Matthew,
Huge accomplishment, but with something the size and capability of that tractor, I think safety needs to be even more emphasized.
I'd consider beefing up some of those linkages a bit and you really need to add a non-interruptable dead man switch or at least a big red button you can push that stops the tractor dead and which is totally not part of or controlled by any of the other electronics.
(The tractor should also stop dead if that dead man signal is ever lost or uncertain.)
Aside from being able to turn your pickup truck into something appropriate for stacking on a flat bed for disposal, that tractor looks like it can drive straight through your house without slowing down.
It is a fantastic achievement, but mostly so far our stuff has been used on vehicles which are pretty much unlikely to kill you.
You have turned that paradigm upside down.
I appreciate that you have somebody in the cab whose job it is to take control should something unforeseen take place, but this is serious business and you really need a hard cutoff totally under your control.
Just my thought, but I would hate to see the headlines if something went wrong.
That said, this is a fantastic achievement and I am sure that eventually a lot of crop tasks can and will be handled by fully autonomously controlled tractors.
I know that some land planes currently use scanned stationary lasers for establishing precise blade height.
It seems to me that a few scanned laser beacons (or reversing it some stationary pentaprisms with a scanning laser on the tractor) could provide precise position control and be independent of (or a supplement to) the much less reliable GPS.
I think that reliance on GPS for precise row farming might be stretching it's capabilities a bit in any case.
That said this is a great leap forward and clearly just the beginning of a whole new way of farming.
Best Regards,
Gary
Your bang on Gary. Minus the lasers for guidance those are all issues I have on my list. We have been using gps on the farm to steer our tractors for years, its been reliable and if you spring for the rtk signal extremely accurate. Im sort of just going on gut feeling at this point but I have spent a lot of hours in a tractor and I do feel that the steering accuracy of this setup is actually superior to the autosteer that I normally use in the tractor. No measurments to back that up though.
The kill switch is something weve been talking about here for a while. It's going to cut the fuel to the engine. I would like enough remotes for every one in the field to have one. Ideally they would be small enough (think cell phone size) to carry on a persons belt or around their neck all day. I want them to have 2 switches one that disarms the pixhawk and one that kills the fuel supply. The fuel supply circuit needs to be totally separate from all the other electronics (just like you mentioned). For sure one remote needs to be set up as a dead mans switch as you suggested. I found a few industrial things that mostly do what I want but I haven't found one with two channels yet. Also they are ridiculously expensive. If it comes to that I'll buy one but I don't feel that paying a ton of money necessarily guarantees good results. Know of any options?
I'm actually surprised how well that linkage is doing given some of the bumps and vibration I've subjected it to but you are right that it needs to be better. (My favourite part is the welding wire and tiny spring keeping it all stable LOL).
But seriously safety is no laughing matter and the kill switch is next on the list. Once I get that working I can do more testing on my own without someone in the cab. I was also thinking about putting 4 swithces (one at each corner) on big arms so that they are away from the wheel so it could be stopped manually from the ground. I welcome any and all input on safety. This is the most important part of the whole thing to get right and many minds will be better than one.
Great job ! Very impressive. But work on the dead man switch. I have a 2000 lb diesel powered tracked bot and I am very glad I designed 3 independent kill systems from the begining. Everything will fail. Cables get loose, switches get stuck, linkages break off etc ..... So now that you have it working go back and put in the safety.
BTW; what GPS do you have on the tractor and what is the accuracy. You said that it was much better than the 3D pixhawk GPS ?
Mind giving me a run down of your safety features? I'm just switching it to a new tractor. I started with the red one bc it had an electric over hydraulic steering valve I wanted to use and now that it looks very promising I bought a valve for the tractor I actually plan to use on my grain cart this fall.
Excellent work Matthew. Just saw this project and I am impressed with your progress. I'm grinning thinking of the fun I would have with this.
When you say your tractor has electric over hydraulic steering, what do you mean? You have a wheel, so I'm guessing it's turning an HMU for piloting a steering valve. Is this right? How is it electrified? If the steering valve is electrohydraulic actuated, then you could probably find a way to actuate it directly with a controller that takes PWM as an input.
Regarding a kill feature, does the tractor have a hydraulic park brake? These are typically fail-safe - meaning you have to energize a solenoid valve to provide hydraulic pressure to disengage the brake. If you lose hydraulic pressure or electricity to the solenoid, the brake applies. This is usually tied into some lock out features in the cab, such as doors, seat belts, etc as part of a safety system. If you have this type of park brake, you could simply interrupt the 12V going to the solenoid with a normally open RC relay switch. That way the RC link failsafe would stop the tractor as well as a tx kill switch. Of course, I would combine this with some type of engine disable as well.
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