Our sprayer has these Wilger boom end valves. They work okay, but they are get very stiff and are hard to turn. They look like this:
Wilger makes a longer handle part, but our local dealer doesn't have any of them. So I wondered if I could 3D print one. I took one off an measured it and modeled it up in FreeCAD. Here's what it looks like:
Surprisingly, it fit on the first try. Here's the printed version:
Installed on the sprayer:
Version 2 with longer handle out both sides
After installing and using my longer handle, I found it worked well, but it seemed like it would work even better if the other end of the handle was also longer. Since FreeCAD is parametric CAD, I simply edited the original shape and changed the dimension:
Installed on the sprayer:
Files
The CAD files, including the printable STL file, can be downloaded from my Google Drive.
Materials
I printed my handles out of PLA plastic. This is not ideal, however, as PLA will degrade when exposed to sun and water. A much better choice for this would be ABS. I only have a PLA-capable printer at the moment, so that's what I'm using for now.
Printing and Cost
The handle was printed on my Creality Ender 3 printer with PLA plastic. It printed with the outside down, 0.15mm layer height, 20% infill, with no supports, in about 30 minutes. According to the slicer, the handle uses 5g of plastic (7g with the version 2 design with the longer handle). If we're conservative and say that 1 kg of plastic cost around $35 CAD, that's $0.035/g, which makes the cost of the part approximately 17.5 cents, plus the cost of electricity. So in this case, it's pretty economical to print up a bunch of these instead of buying the Wilger handles at a couple of dollars (guessing) a piece.
RTK GPS positioning has always been something we were interested in for our tractors and machines, but we could never justify the cost. Over the years it's become more affordable for farmers. RTK requires a fixed base station that monitors GPS signals and transmits observations to roving GPS units. The roving units use these base station observations to correct position error down to just a few centimetres. In the past the big ag companies required you to buy and set up your own base station, which was quite expensive, to say nothing of the cost of licensing the software unlock for the roving GPS units. With John Deere it's still very expensive and proprietary. But for other brands, things are looking up. Also we just bought a used machine that happened to have RTK capability unlocked on the Trimble 372 receiver, so this post is about setting up my own GPS base station for it using the uBlox ZED-F9P RTK-enabled, GPS receiver.
RTCMv3, the Standard for Base Stations except John Deere
John Deere refuses to cooperate with other brands, so all John Deere receivers require a special John Deere base station. Not so for Trimble and others. These receivers in recent years allow the processing of observations using the industry standard RTCMv3 format. So any base station that can generate these messages, and transmit them somehow to the roving units, can create a working RTK GPS system. John Deere receivers can process RTCMv3 messages just fine, and the very expensive, commercial construction units do. But for ag machines, Deere has locked this feature out entirely. I've heard rumors there is a way to unlock RTCMv3 support by getting something called "Mobile RTK" but I haven't found much information about that, such as the cost.
Trimble 372 and RTCMv3
As mentioned, modern Trimble receivers, such as the 372, can establish RTK fixes using the RTCMv3 observation messages, provided your receiver has the RTK unlock in it, which costs $3000. This money is simply for a code that unlocks the functionality already present in the receiver. I've heard rumors that buying a Centerpoint RTX subscription also enables this functionality, but I doubt them. By complete luck, the used farm machine we recently purchased came with a 372 receiver unlocked to RTK.
How To Get RTCMv3 into the Receiver
The 372 has two ports on the receiver itself. The main one is called Port A and it is the main communications channel to the machine. This port includes both a CanBus link, providing j1939 messages to everything on the isobus, and an RS232 link, which provides data via the TSIP protocol to the navigation computer (the autosteer controller) and also to the AFS700 monitor.
The second port on the 372 contains two serial ports, Port B and Port C. Port C can be configured to input or output a variety of serial protocols including NMEA sentences, TSIP, CMR (a proprietary RTK obvservation protocl) and RTCMv3. We are primarily interested in RTCMv3 on the input (RX) of this serial port. Digifarm produced a YouTube video describing how to configure Port C for RTCMv3:
RTCMv3 data can come from a variety of devices including a radio modem, a cellular link (a computer with a cell data link), or even via a bluetooh to serial adapter.
RTCMv3 Through The Internet Via NTRIP
Any RTCMv3 messages that are transmitted via in internet connection usually use a protocol called NTRIP. This is based on HTTP. Although it's not secret or impossible to implement, I've been unable to find any open source implementations of an NTRIP caster). There are several services in North America and the world that offer RTCMv3 messages via NTRIP, sometimes for free, or for a subscription. For example, Digi Farm's RTK network, various US government CORS stations, or RTK2Go which is a free service that farmers can send their base station data to, and pull down using NTRIP on a rover.
If a bluetooth to serial adapter is connected to the Trimble 372 Port C serial port, observations can be retrieved via NTRIP on a smartphone using the LeFebure NTRIP Client Android app, and then then sending them to the 372 via a bluetooth link with the serial port adapter.
RTCMv3 direct via serial link (radio)
RTCMv3 messages can also be passed directly to the 372 from a radio modem talking to the base station. Any radio modem will work, provided you have the proper cable set up, and provided the RTCMv3 message types the base station is transmitting are the required types. More on this below.
The wiring for Port C is pretty straightforward. The connector that plugs into the Trimble needs to be a Deutsch DTM-06-12SA. The pinout can be found in the 372 manual, on page 23. A cable would look something like this:
Different serial devices might be male or female, and some devices are meant to be plugged into a computer, and some are meant to act in place of a computer. So you may need to swap pins 2 and 3 on the serial end. This can also be accomplished with a simple null model adapter.
Radio is the primary route I decided to go. Here are some pictures of my radio receiver to RS232 adapter:
All that it consists of is a Digi SX radio, flashed with hopping firmware (it just listens; it doesn't need to transmit anything), a 3.3v serial to RS232 adapter, and a little 12v to 3.3v power adapter. The radio connects to a 900 MHz antenna on the roof, and the RS232 connects via the cable described above to Port C on the Trimble 372.
What's required for Trimble 372 to RTK fix with RTCMv3
After a lot of trial and error, and many failed attempts, I was finally able to determine the minimum RTCMv3 message types Trimble requires to fix RTK. They are:
1005 or 1006 - Stationary RTK Reference Station ARP
1008 - antenna descriptor
1077 - GPS Multi Signal Message
Optionally:
1087 - GLONASS multi signal message
1230 - GLONASS L1 and L2 Code-Phase Biases
DIY Base Station
All that's needed at this point is our own RTK GPS Base station that can offer the required RTCMv3 message types. In my next blog post I will show how I did this with a low-cost uBlox ZED-F9P integrated RTK GPS receiver, an Arduino, and a Digi SX Pro radio transceiver.
