Hello everyone! So the other day when I was taking this DJI FPV drone out for my second time it was
a very windy day and I happened to notice that when I was flying with a really strong tailwind
that the display in my goggles that shows you your speed was maxing out at 99.3 miles per hour
99.3 mph is as fast as it will at least tell me it's going no matter how fast
you go. It seemed to just stop right there so I was really suspicious about that. I
wasn't sure, is the drone actually slowing down to exactly that speed or is it just your speedometer
pegging the needle and not showing you that you're going any faster than that
and I figured I would take a little deeper dive into that and try to figure out which was true.
So the first thing I did was I searched google for the DJI FPV drone going 99.3 miles per hour
and one thing that I came up with was this reddit thread where somebody else noticed
the same odd behavior that they were pretty sure they were going faster than 99.3 miles per hour
or they hit that limit and then could still visibly go a little bit faster than that
but there they believe that it looked like the speed indicator was maxing out at 99.3 and I have
to agree, that's sort of what I was seeing in the goggles as well. So let's see how else can we test
this. It turns out that the DJI drone will record a subtitle file. This .srt file here
along with the video file on the drone and in that file it saves the longitude and latitude
of where your drone actually is and we can use that to calculate the drone's speed.
So let me open up this file in a program like vlc where it will show you the subtitle track.
Here you can see I have it loaded right before I'm about to go flying as fast as i can across this
field with a really strong tailwind and down at the bottom you can see the longitude latitude
and the time. I need to record what time this was. This is at 9:02 in the morning and it was 0
9 seconds 0.202 and then I'm going to take this latitude and longitude and put it in this website
which helps you calculate the distance between two latitude and longitude points
and we've got forty four three thirty three
one nine five one ninety three nine eight 7
1 0 1 and then we have to find our second point that we want to measure the speed
between so I'll just play this video ahead a little bit when I'm going fast.
I'll pause it here and let me bring my web browser back up again.
All right, point number two is 4433 one whoops zero nine eight and the longitude is 93986375
all right and this website actually shows a handy little satellite map of approximately
where we were and this is an old aerial image but it does show me pretty much right where I
was flying and you can see that the distance I traveled was 0.1110 kilometers and now I know
it's pretty simple calculation to figure out speed but I'm lazy and I don't want to do it
wrong so I'm going to use this speed distance time calculator. Oh I actually also have to measure or
write down this other time. Make sure I get that right. Nine zero two eleven point six zero five
Okay so I'm going to copy the distance I got here which is 0.1110 kilometers
and I'm going to put that in here for my distance
and then I need the speed or the amount of time it took me to go that distance so I'm going to
bring up my calculator here and I'm going to subtract that second time which was 11.605
and take away 9 and that'll tell me it took me 2.403 seconds to go that distance
2.403 seconds and tell it to calculate the miles per hour and we have 103.329 miles per hour
for this particular flight. Let's play that back again.
So this is the DJI FPV drone apparently going 103 miles an hour, which for those of you who who
know your FAA rules is approximately three point something miles per hour over the limit so shh
don't tell the FAA that this drone was flying three miles an hour over the limit for a
few seconds. Anyway, so there you have it, that's the answer. The DJI drone will stop displaying
your speed and won't go any higher than 99.3 miles per hour no matter how fast you're going. I have
no idea why. I don't know if they're trying to not show you that you're breaking the FAA speed limit
or if there's something else going on with their calculations they can't go higher than that
I'd be really curious if anybody does know the answer to that because I'd really like to know
but just so you all know if you do see that maximum speed limit in your goggles that's
where it's coming from. I suppose I should really test and see if I switch it to kilometers per
hour if it also has a similar speed limit that corresponds to 99.3 miles per hour
anyway curious to what everybody out there thinks about this and thanks for watching!