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?
That's something I'm interested in as well, not sure when I will find time to experiment so if you do any work in that area keep me informed or start a thread here.
Thanks tractor is still working great! There is just no way we are ever going back to a driver for this application.
Hope harvesting going well, we haven't got started yet here in UK (Scotland) but hope to in next 10 days if weather plays ball.
Was wondering if there is any object avoidance (utility poles & pylons, water wells, wet holes)?, was thinking like geo-fence around feature.
We have 10 objects in 1 20acre field and not fancying felling electricity power line!
A sonar on the front (or 2) will enable the vehicle to detect the object and it will make a decision regarding going left or right around it. However, it wasn't designed for large vehicles with slow turn rates and the effect range of the sonar (7m to 10m) probably isn't far enough for your purposes. We would need to test.
The other alternative is LiDAR which goes much farther but again you would need to test.
At the moment there is no way to specify an object in the driving area and tell the Rover to avoid it. Rover doesn't currently support geo-fence's but its on my list.
Do you not think sonar would struggle to see something like this?
Great work to date Grant and hope geo-fence can be added at some point.
Hey Grant being able to specify an object in the driving area and tell the Rover to avoid it would be great! It would also be nice if there was a way to update that list of objects from the GCS. If you keep adding the features I need before I get around to working on it I'll never get a chance to contribute to the code :)
I found an old issue that had been raised on this:
I won't be implementing this soon. I've got a few other features to put into place first so you have a good chunk of time if your keen.
Congratulations Matthew, great job.:D
Fantastic Matthew - glad it worked so well and you didn't have any failures! With that amount of testing it has proven very reliable.
Hey Jaakko I looked through your list. The connections on every tractor are going to be unique to the model. Essentially you have to hook up actuators to all the relavant controls in your tractor. How this happens exactly will depend a lot on the type of transmission your tractor has. Even the individual actuators have to be specd for speed, stroke length, and strength depending on how hard it is to move the controls. This really needs to be done on a case by case basis. I think I documented fairly well in these posts how to make the connections to different gps modules that were already on my tractor. The best way to begin on this type of project is just to get started. Buy a pixhawk and a cheap rc car and build up from there. Once you get the pixhawk to work in an rc car you will have a much better understanding of how to proceed to get it in your tractor. If you have more specific questions as you get going I will be happy to help.
Ok so I finally got my grain cart control software up on GitHub. https://github.com/mattdreimer/AutonomousGrainCart
There are some notable issues with it.
1. It is still version 1 of droneapi so must be launched from mavproxy
2. It is a gui but does not take into account different screen resolutions so it may look very bad if you don't have the same screen resolution I do.
3.There are likely many things I did wrong from a general programming standpoint b/c I am a beginner. It does work though. Feel free to make corrections