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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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.
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.
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,
Jaakko
This is on my Christmas wish list now. This project was so cool that I had to join the forum just to contribute my $.02.
As an alternative to your emergency stop button bar have you investigated proximity sensors? We had a remote trench packer here at the farm for a while and they had a proximity sensor on it that would lock out all movement if anyone was within range of the sensors. I am pretty sure that it would be ultrasonic but maybe there is some other device. My thoughts would be to have a long range sensor looking to the immediate front of the tractor it would have to be set so that if the tractor is going full speed and it picks up a signal there is enough time for the control system to hit the brakes. this might also be useful on the sides if someone wonders up to it without thinking about it, but you could have that set much less like 4 ft or so. the side proximity sensor might also help you avoid running the grain cart into the combine with you having to pay attention to it all the time. You also might consider having a secondary proximity sensor on the front that is set much closer and it would act as a failsafe and should be completely separate from your pixhawk controller, if it picks up anything it assumes that the pixhawk is not working and dynamites the system.
A possible test would be to setup a stack of 5 gallon oil pails as a human analog and drive the tractor towards it to see if it will pick up the pails and stop in time.
Sorry for the novel on my first post, but this is a really cool project!!
Hi Robin,
I had old information. Please lookthis (SF01) and this (SF03) link.
Hi Robin,
please, look at my PDF file attached previous message and page number 10. There are two options for range sensors and link to webpage too. They are cheapest what I could find in this sector. Unfortunately I can't use those in my application because of dust.
But, I think main problem with those is that you need controller to analyze and calculate signal. I asked them to do such a board, but they said that if I order more than 10 units then they will do it. I wanted board where I can connect and use like relay. It takes too much work to do it.
You can use a Rangefinder (sonar or laser) currently with a Pixhawk. You can configure how close you need to get in order to take action - parameters are:
RNGFND_TRIGGR_CM = 100
RNGFND_TURN_ANGL = 45
RNGFND_TURN_TIME = 1
At this stage the action is to navigate around the obstacle but we could enhance that code to be configured to do a number of things (HOLD, go left, go right, auto navigate around, reverse, go to way point) if there is enough interest and people would use it.
Thanks, Grant
you are one of developer I assume. I would like to have that part of settings like I could set example three steps how rover/tractor slow down. When Object or person is 30ft speed decrease 30%, person is 15ft speed decrease 60% and when person is 10ft from vehocle it will stop. Maybe also possibility add how long vehicle need to wait until it can continue.
Safety will need to make separate way from this. It is something else.
Best regards
Jaakko
You are right about needing the safety systems running separate from the pixhawk, it creates redundancy.
Thanks for the input. Keep posting as you have ideas.
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