Hi, most of the Forum readers might know the importance of GPS lock to prevent fly-aways and expensive irregular crash flying. Newbies be aware!! Don't only rely on the nbr of sats you see on the ST16 and H. You have to have GPS lock and depending on your last flight and recent position you maybe have to wait almost 13minutes before take off. Pls read this http://www.measys.com/docs/TTFFstartup.pdf and save $$$
GPS lock importance
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A good post, it adds to our understanding of GPS units.
Note however, that this link refers to a specific product, the IKE GPS module, so certain of their guidelines may not apply to the TH GPS system.
Note however, that this link refers to a specific product, the IKE GPS module, so certain of their guidelines may not apply to the TH GPS system.
Hi Rayray, in what way doesn't this apply to a H? The GPS almanac and lock "rules" are important for all kind of GPS recievers. Or??
This statement is a built in logic so the typhoon H may not try to acquire SVs for 15 mins before doing a cold start. It may only try for 1 min or 2.
"However these SVs will not be overhead. It will try to acquire these SVs for up to 15 minutes
before reverting to cold start mode, and therefore in these circumstances may take 20
minutes to establish a fix."
"However these SVs will not be overhead. It will try to acquire these SVs for up to 15 minutes
before reverting to cold start mode, and therefore in these circumstances may take 20
minutes to establish a fix."
People also often confuse the GPS in their vehicle and speed with which their position appears on a map. This is not the same. In most map GPS you have a 2D location. In a drone you have 3 spacial coordinates plus time for a 3D coordinate which is much more complex and requires time to download from multiple satellites for increased accuracy.
Gwhuntoon, what's your view/recommendation to wait before take-off IF you haven't flown for a week or so and maybe will do it 100miles away from last point?
Case in point.
When I went out to fly the other day, it had been 2 weeks since I last flew my H from my house.
The AMA field is probably less then 15 miles as the crow flies from my house. When I powered up the H on the first battery, I had 14 Sats in less then a minute. It took close to 5 minutes and 20 Sats before I had the GPS ready light up. It can take time to acquire a GPS FIX. On the second battery, had the GPS ready in about 30 seconds.
Remember the # of satellites in the display is only the number the H is receiving a good signal from (LOCK), it is not until it has acquired enough good data that you get a GPS FIX ( the H now knows where it is).
Your ST-16 must also acquire a GPS fix before the H will give you the WHITE flash in the tail light. You can fly with out both having a FIX. Just RTH and other SMART mode function will not work.
Good point to remember.
Your car usually always starts back up from where is was last powered off. Your H may be different.
When I went out to fly the other day, it had been 2 weeks since I last flew my H from my house.
The AMA field is probably less then 15 miles as the crow flies from my house. When I powered up the H on the first battery, I had 14 Sats in less then a minute. It took close to 5 minutes and 20 Sats before I had the GPS ready light up. It can take time to acquire a GPS FIX. On the second battery, had the GPS ready in about 30 seconds.
Remember the # of satellites in the display is only the number the H is receiving a good signal from (LOCK), it is not until it has acquired enough good data that you get a GPS FIX ( the H now knows where it is).
Your ST-16 must also acquire a GPS fix before the H will give you the WHITE flash in the tail light. You can fly with out both having a FIX. Just RTH and other SMART mode function will not work.
Good point to remember.
Your car usually always starts back up from where is was last powered off. Your H may be different.
In-car navigation systems sometimes also merely use GPS information to place the vehicle icon on the nearest road. If you pull into a parking lot the map may still show you on the nearby road. Accuracy for vehicle navigation is far less critical than it is for a drone.
The 100 miles has more to do with compass calibration but yes, 12.5 minutes with a single GPS is typical from a cold start or 35 days or more. Only a week is relatively high accuracy. While the GPS retains the almanac it's out of date. To be safe I just wait the 12.5 minutes. There is usually prep work and prestartup checks you should do which will easily make that 12.5 minutes fly, also the drone sitting idle for 12.5 minutes barely uses any battery.
The Typhoon H uses a u‑blox 8th gen chipset which provides correction data valid from 1 to 35 days. Positioning accuracy decreases with the age of the correction data, with 1–3 day‑old data providing relatively high accuracy and 10–35 day‑old data progressively less accuracy. Regular updates help to ensure a high level of position accuracy. The u-blox is rated at
Time-To-First-Fix for GPS & GLONASS (Cold Start) : 26s (Open Sky)
Acquisition
Cold starts: 26 s
Aided starts: 2 s
Reacquisition: 1.5 s
Theoretically you could startup faster that 12.5 minutes, however a lost drone will make that theory academic.
Don't confuse GPS accuracy with GPS Ready. Only time to update the almanac will improve accuracy. While the GPS may be ready when you hover you may see the drone drifting slightly. Some of the drift is relative to less accuracy. When I wait I find my H hovers much more steady. Well, for me it's steady, at least the video is rock steady. Still amazing to me given the price of this drone. Uwe Loewer has a good video demoing the difference between GPS on and off, accuracy falls somewhere in between.
Presumably it continues to update whilst flying, even if you take off before it's fully updated?
Possibly, and logically you could assume that but I've learned to assume nothing. The true is, I just don't know and don't want to risk my drone to find out. I prefer facts to alternative facts.
I am not sure you are right about this. My GPS map unit gives altitude as well as lat and long so it must use 3D fixing!
Wow! That's really useful information. Some of this has been tossed about on the forum without much technical documentation for backup. My experience, which has been confirmed by Yuneec CS, is to simply wait for the GPS READY indicator on the ST16. Sometimes it takes a long time, other times it happens before the camera is linked.
Check out this flight, which was after my H had been sitting unused for a week or two. The GPS accuracy is shown in the chart on the right below the video:
UAV Toolbox - Yuneec ST-16
You can see that the accuracy drops rapidly in the first thirty seconds after start up, and then stays pretty much constant. I'd need to check, but I think the sat count was around 15 by then, and increased to 20 by the end of the flight - but accuracy didn't improve very much past the initial start up.
UAV Toolbox - Yuneec ST-16
You can see that the accuracy drops rapidly in the first thirty seconds after start up, and then stays pretty much constant. I'd need to check, but I think the sat count was around 15 by then, and increased to 20 by the end of the flight - but accuracy didn't improve very much past the initial start up.
Interesting. Did you recall if you got the GPS Ready indication on the ST16 at 30-seconds from startup? I guess, I could do a test myself, duh...
The GPS error (not accuracy) dropped rapidly to the 1-2 ft range.
It's worth pointing out that those documents are for a different machine with a different GPS module, so cold start and almanac refresh may (and some people believe do) behave differently on the H. The suggestion is that the H's GPS module is a newer generation that has better start up characteristics.
No, I didn't time it - something for the next test flight
One interesting point is the little 'blip' in GPS accuracy comes where I had landed the H and was standing over it. Of course it's confusing to call it GPS accuracy (it's the amount of error estimated in the GPS position), but as Yuneec refers to it as that in the telemetry data I try to stick with their terms.As a complete aside I had a fun little problem with one telemetry file from a user that kept crashing my app. It turned out that he'd just had the GPS module replaced, and the engineers had given it a test flight. The reason for the app error? From new, the GPS module in the H defaults to a date of 2014 until it picks up enough satellite information to set its clock accurately. So in the telemetry, the flight appears to start in 2014.. then suddenly jump to 2017. The app was trying to estimate a flight three years long, and running out of memory in the process!
