Long term user of FarmerGPS here looking to switch to AgOpenGPS to take advantage of the autosteer / section control functionality, and also just because I am a bit open source kind of guy!
My question is, I currently use a starfire 3000 receiver as my GPS antenna, using the serial output to connect it to the tablet in the cab. Obviously the starfire unit has a gyro for roll / tilt compensation, will this work with AgOpenGPS? Or will I still need a separate unit? I dont know how the deere system works but assume is normally just sends this data to the deere display, and then the display does the calculations based on vehicle / implement etc to correct the GPS streams data? I have no idea if it sends this data on serial also? And if it does, if AgOpenGPS is able to use it?
No, I don’t know, this is essentially what I am asking as I am unsure…
For it to be able to accurately modify the NMEA strings, it would need to know the vehicle information its on right? (IE height from ground) Obviously when its hooked up conventionally in greenstar (which is what I use on the combine hence using it here also) you set this all up on the display per “vehicle” but I dont know if that information is passed to the GPS unit and then it fixes the nmea streams, or if its processed separately in the display, I am thinking the latter…
The actual tilt / roll numbers themselves arnt, but your current location would have to be based on the tilt offset of your current GPS position, which is directly related to the height from the ground, as obviously the further in the air the receiver is at x deg of tilt, the more to one side it will be reporting it is compared to where it actually is.
As you say Brian, I don’t think the receiver does these calcs, so guessing ill have to have a separate sensor, which is a shame as the SF3000 is super super smooth has really good terrain compensation I have noticed in the combine!
Has anyone else on here got any experience with the SF units and serial output?
I use a SF3000 serial output on the my sprayer with an agleader ontrac. The nmea data is corrected for roll by default. I turn the TCM off in settings on the Greenstar display otherwise I would be correcting for roll twice. If you wanted to use the TCM you could set the correct height in the greenstar before you took it off.
As it happens I’ve been looking at my StarFire receiver lately and from what I can tell, the Starfire receivers do no roll compensation at all. They do have a TCM module that measures roll and keeps track of fore/aft position and height, but as near as I can tell that data is passed over the can bus to the navigation computer (is that in the monitor or separate like Case?), which does the integration in there. I came to this conclusion by observing the position data on RS232, on the Starfire info page on my GS monitor, and by observing the can bus messages coming from it. Disabling or enabling the TCM did nothing to the latitude, longitude, and altitude numbers. Now it could be that SF1 accuracy doesn’t have enough precision to show me a change in altitude of 2 meters and the other offsets aren’t that big. I’ll have to double check things, but so far this is what my tests reveal…
Certainly the RS232 NMEA output is not corrected for roll. I proved that a long time ago with AOG’s calculated heading (it was ver wavy due to the tractor rolling back and forth).
Again I’ll test it again. If I park on a tippy spot, I should see several differences between the position with TCM on and off.
Interesting, as KJM above seems to think that it is?
I must admit, I didnt know that it was, and assumed it was all done in the temrinal in the cab, as would always depend on the particular vehicle / height etc to make the correct correction, and didnt think it would pass this info to the receiver…
Only thing that makes me wonder if it is, is that I have been running FamerGPS for many years, using the serial output on my SF3000, and I have to admit, it works extremely smoothly / accuratly, and 99% of my farm is on a hill, in places very steep…and it you can go from level to slant very fast, and it stays straight ahead…which in my head, if it wasnt correcting it, it would shoot off to the side as the tractor lurches over on the hill…So I really dont know at this point!
Just having a thought, I wonder if it makes any difference if you are using the receiver on its own…or if its in a tractor with a Greenstar display connected with vehicle etc selected, wonder if the display as any way of sending the data back so the serial output is then corrected based on what is selected on the display?
As it happens I do have a 2600 display which I mount in the tractor (out of the combine) but i never really use it for anything much as I use farmer GPS, and now want to use the autosteer of AgOpenGPS, to save buying $$$ deere steering valves etc to make my standard display work. I only have that because my combine already has all the Autotrac parts on it, so just made sense.
I don’t know either! I will do more investigations, though, as this stuff that I’m already looking into for another project unrelated to AOG. All I know is the GPS information going to the navigation system (I altered the longitude data to move the tractor over a couple of feet and it works so the nav system is using that data) is the same as the position data in the NMEA output stream. And I also know that the TCM data is being transmitted on the bus, because when I hook up a 3000 unit I have with a bad TCM, I can see the bad data on the bus (it’s all 0xff’s) and the tractor won’t steer, no matter if you tell the receiver to turn off the TCM or not.
I guess you could park on a hill, turn TCM on and off and see how the NMEA data stream is affected.
But I did initially suspect that the GPS data was compensated in the receiver, at least to the NAV computer. However the fact that I’ve always gotten really wavy data out of the serial NMEA stream on my 4wd tractor, and that I’ve verified the same positions are going on the bus as the NMEA cast doubt on that. And that I haven’t been able to observe any changes to the GPS position data when I disable the TCM (which I plan to test again soon).
Unrelated, but down the road I’m convinced it’s entirely possible to drive the John Deere steering valve over the bus. John Deere’s messages aren’t encrypted, but they do try to verify that the modules are all Deere approved. But if I left the deere stuff in place and just modified the data, I believe AOG could drive the tractor. Later on I may try to see if I can find the messages for the steering angle sensor.
Wish I could edit my other post and cross it all out… I’m definitely wrong. Tonight I verified that, in fact, the starfire receiver does integrate the roll (and almost certainly the offsets) into coordinates it sends over the can bus, and also the coordinates displayed on the info screen. I parked on a snow drift and toggled the TCM on and off and the coordinates definitely moved consistently and the distance from my line shifted consistently. But even more definitively, when I overrode the coordinates going on the can bus with a special can filter I’m playing with, when switching on and off the TCM, the line didn’t move at all. I didn’t have my serial adapter with me, so I couldn’t double check the serial NMEA output, but I will do that. In the meantime, @darrenjlobb, it looks like you should be fine with taking the data straight from the Starfire into your AOG setup.
@BrianTee_Admin when you said your timble outputs coordinates that are already compensated for roll, are you getting this from the back of your AFS monitor or from the receiver on the roof via port C? As I understand it, the Nav computer itself (usually a box mounted under the seat) as the accelerometer in it and I presume does the integration there, which led me to erroneously deduce the Deere system did the same thing.
My understanding on the Case/Trimble stuff is that the signal is only corrected for tilt etc if it comes out of the Nav controller from under seat not port C. Have never tested it but most stuff I have read Case wants you to get nmea data from the Nav not Port C. Now I am wondering if the Nav nmea data would have a steering angle in it as well because that is hooked into same system. Any thoughts
On my sprayer, the Aim Command Pro system is fed NMEA data for mapping and turn compensation from the Pro 700 somehow, and that is pre-corrected data, at least according to the Aim Command Pro manual. I haven’t taken a good look to see exactly where the cable comes from, nor have I dug into the Pro 700 to see if there are configuration options to set up the serial feed.
EDIT. So according to this PDF, the feed actually comes off the NAV II controller box. The sentence frequency and types are set up in the Toolbox->NAV tab. http://talk.newagtalk.com/forums/get-attachment.asp?attachmentid=240804. I believe this will be position data only (no steering angle). And the position will be compensated for roll and offsets so that it’s nearly ground level, on the rear axle, or thereabouts.
The IMU on my Case 500HD is on the articulating joint, top hinge. I’m taking the rs232 from the can connector of the nav computer using an adapter cable
Is it a little black box about 2"x2"? They use that on my sprayer too, but it’s mounted to the front right wheel where it doubles as a steering angle sensor as well as an IMU. I believe it’s an expensive little unit if it ever failed. I bet it’s got a 6dof IMU sensor inside it. I’m not sure whether this is doing roll measuring for the NAV II computer or just steering. I was under the impression that there is an inclinometer inside the NAV II unit. I’ve never looked at it closely before, so I’m probably wrong.
Hmm, I’ll have to add that to the list of things to explore with my little can bus interceptor which is an arduino Due with a dual CAN tranceivers attached to it and code that bridges messages across the two interfaces, allowing for filtering and dumping of data.