Thanks for the excellent writeup. Where I work, we have Piksi, Piksi Multi, Here+ and TinyRTK.
Piksi mostly works, most of the time but I personally wouldn’t trust it on an aircraft. It occasionally seems to almost get distracted by a shiney object and it stops sending position updates to the flight controller which causes the pixhawk to act as if the Piksi just fell off the aircraft for a few moments until it restarts sending position updates.
Piksi Multi seems to have a lot of difficulty pulling in signal. A M8N will easily outperform the Piksi Multi unless you’re in an open field and then the Multi will probably get RTK Fix. The Multi is HUGE and heavy and thus far we’ve only been able to get it to work with the correction radios included with the dev kit which are also large and akward to install. We briefly tried to get injection working over MAVLink but with no success at all. I actually have a few helical Harxon antennas coming and we may try to put the Multi on an aircraft. Thus far, we’ve only been testing it on a UGV since the pile of boards and cables is just so ridiculously big akward and heavy. It honestly looks more like a prototype than a finished product.
Of the M8p based systems, the TinyRTK is my current favorite but it seems to have some strange characteristics. When operating in GPS + GLONAS mode, it seems to be only able to send RTCM correction messages on a regular interval for one of the two constellations. It also seems to regularly drop GPS and/or GLONAS lock at a regular interval despite very good satellite signal strengths. The M8p goes into RTK Float very quickly but after messing with it for months, I’ve only seen RTK Fix 2 or 3 times for a very short period of time. In my experience, it seems to do better if you set it for a single constellation (GPS or GLONAS) and use SIK (or similar) radios to directly send the correction data. My gut tells me that either the firmware on the M8P needs to be optimized and debugged or the onboard processor is just too slow to do the math. I hope to do some more testing later this week and hopefully, finally figure out just what exactly is going wrong with it.
I don’t care for the Here+ at all as the rover can’t use an external antenna and the inbuilt antenna performs very poorly. A TinyRTK with the small Tallysman antenna will easily pull in 15db-hz more signal with far less noise. Also the lack of easily accessible USB/Serial out on the rover and base makes troubleshooting the system close to impossible. For my testing, I ended up loading the rover firmware on a second base Here+ and soldering in the serial connections myself. I’ll probably end up installing the Here+ rovers I have on aircraft to use them as expensive standard GPS units.
For what it’s worth, I’ve also seen an Applanix APX-15 UAV (Trimble) system work and it is phenomenal however I was able to find out that it is $9k-$18k per system depending on quantity, etc. It produced ~1-2cm results in an area that I seriously doubt the Multi would have been able to get a fix or even GPS lock in.
Been flying with a Septentrio AsteRX for several months. Started out with an antcom G5-1.9 antenna, which requires a 5 inch ground plane. The antenna was a bit heavy and the ground plane was bulky, so we swapped it out with maxtena helical antenna. Much lighter and no ground plane required. Simple to integrate with the pixhawk, virtually plug and play Performance seems to match the ant G5 with ground plane.
I have access to a state wide VRS network, which we use for the correction. Send the correction with Mission Planner through the telemetry radios. Goes to a fixed solution within seconds of getting the RTCM message. Rarely do I lose a fixed soluion once aquired.
This a great product if you need consistent cm level accuracy. I recognize it’s several times more expensive than the L1 solutions mentioned here, but for me it’s a necessary and worthwhile investment.
Today, I finally saw the M8p going in and out of RTK Fix. I suspect there was very little interference today and probably just a little bit of dumb luck.
All the same, I’m looking into the ComNavTech k501g.
I too used the piksi and it showed the same symptoms you mentioned. I currently use the emlid reach and it’s serving me quite well without any issues at all. I have used it on an XUAV talon and the RTK status is very consistent.
For what it’s worth, a guy in our lab found a few bugs in the Pixhawk’s Piksi drivers and I think he may have also found a bug somewhere else. Either way, after we can test this some, the Piksi may be slightly closer to working correctly.
While this is true and I did use a Here+ Base as a rover, it requires soldering in wires to break out the serial output which is not an easy task given the amount of ground plane on the pcb. This one of the reasons why I say the TinyRTK is my current favorite M8P board as it has all the right connectors and doesn’t require any soldering.
Hi Robo_Roby something that you may be interested in, the M8P can output all the raw data you need for RTKLib, It would be very interesting to compare the results of running RTKLib on the M8P and compare the results…
Also for mission planner users of all the m8P based systems, a pull request has gon in to fix a bug in 3.5 that could possibly be affecting the ability to maintain an RTK Fix
@Prototype3a You only need the boards. Board output is serial and antenna can be purchased cheap on ebay/Aliexpress. If ComNav won’t play nice, I’d be tempted to contact Unicore (UB352) for L1/L2 GPS/GLONASS (600 USD last price I heard). Alternatively the M8P is getting quite good – at this point you’ve got options.
Hi, has anyone been able to load m8pv1.4 firmware I tried and failed and now can’t load messages,I think fis file is missing and I can’t find it anywhere, any help would be great…thanks in advance
Sorry that I just saw this… maybe you’ve already sorted it.
The FIS file is in the Ucenter program folder (at least on my windows machine). That one threw me for a loop as well.
For what it’s worth, our lab has been playing with the Swiftnav Multi lately and my conclusion is that the Multi is very optimistic on claiming that it has RTK Fix where the Ublox seems to be extremely conservative and won’t claim Fix unless it has had consistent and stable fix solutions for many MANY seconds. I believe Ublox datasheets say something like 30 seconds where the Swiftnav seems to claim Fix after maybe just 2 seconds.
Either way, I’ve seen both systems work and totally not work depending on location, if you’re standing just right or the alignment of the planets. Neither has been reliable or a state that I would consider “deployable”. The only major upside to the Ublox that I’ve seen is that it doesn’t do anything stupid when things aren’t working properly. It very smoothly and seemlessly falls back to either single point position solution or RTK Float.
I still really want to play with a ComNavTech but I doubt I’ll be able to get funding for that adventure.
We got our hands on a Harxon HX-CH4601A helical to use with the Swiftnav Multi and it seems to perform very similar to the Maxtenna helicals but at around half the cost. The shipping from … Taiwan?.. was very expensive so I would order a few at a time if you need them or try to negotiate a cheaper shipping method.
