Good day! A lot of us FPV pilots like to
use these small GPS module receivers to activate Betaflight GPS Rescue
on a switch if we lose our video feed or as a failsafe for a loss of control
signal. If you need a refresher on how to do that
make sure to check out this video linked in the description below. When
these GPS modules have a satellite fix they work great for those applications -
whether you're flying your Diamondback Rattler lightweight micro FPV quad
long range or even short range over areas where fail safe set to "drop"
won't do you any good. But if you're like me, one frustrating thing about using these tiny GPS module receivers
can be waiting around for them to get a satellite fix after you plug in your
lipo and before you can launch your quad. Today I'm going to show you how you can
reduce and minimize the amount of time it takes for your GPS module to get that satellite fix. I'll briefly explain
what's needed for a satellite fix, list several ways you can minimize time to first fix, and I'll demonstrate two "special things" you can do to speed up that process to get you in the air
sooner. Sound good? Then give this video a "thumbs up" below, share it on your favorite social media
platforms, and subscribe to your TMac FPV channel -
your home for your Journey to Better FPV fun, flights, and racing stuff! First let's look at our satellite lock
or fix requirements, where GNSS stands for global navigation
satellite system. I point this out because what's normally
referred to as your GPS module may actually receive signals from
satellites other than GPS, such as the Russian Glonass system,
Europe's Galileo, China's Beidou, Japan's Quasi-Zenith satellite system, or
India's NavIC satellites depending on your module type and where
you're located in the world. Your module needs the current, very
precise time which it obtains from the satellite
messages and is saved to a battery backup RAM for use with its internal real-time clock. It also needs to know its
position which it calculates from those same received satellite signals
and saves to any memory which your module may have. Finally your module
requires valid ephemeris data for at least four
satellites, and for Betaflight Rescue, the minimum
is five. This ephemeris on each satellite is very
precise orbital positioning data and it's good for only a maximum of four
hours. This is because the navigation satellites actually move in the sky,
as depicted over here. If you're this blue dot on the globe,
at the same time your module is moving the earth is rotating, and
the satellites are moving in space as well. They don't have a geostationary
orbit like the communication satellites you use for your DirecTV or Dish antenna
and throughout the day your module won't be receiving messages from the same
satellites. As a matter of fact, the satellites in
your module's field of view in the morning aren't going to be the
same satellites it sees later in the day. Your module needs all of this data to
lock on to at least four satellites and a minimum of five for Betaflight GPS
Rescue. So the first time you power on your module for the day,
it's basically waking up and saying "Where am I and what satellites can I see?"
If it's starting from scratch it has to scan the entire sky within its field of
view. But if it's stored what's called a valid
almanac, it won't need to scan the entire sky for
any satellite because it will already remember which satellites are in its
field of view for that time of day. So this general orbital positional data
(which is not very precise) on all the satellites gives it basically a
boost or a head start to lock onto satellites for its first
fix of the day. There are three modes which your module can start up in:
cold, warm, and hot. You'll usually see these three modes
in the product description of any module you're thinking about buying along with
their advertised acquisition times. What you need to know
about these is they're based on an open sky and with a
module operating by itself with no other interference or electrical
noise from other components. The first mode is
called a "cold start." This is when your GPS module doesn't
have any information anymore from its last fix. When your module starts up in this mode, when powered on with the rest of your
quad's components, it could take several minutes to get its
first fix. I'm going to show you in just a bit
how you can reduce this amount of time. The second mode your module can start up in is called a "warm start." This is when it does have some of the
information from its previous fix stored in its memory such as the almanac
which I mentioned earlier along with a precise time from its
internal battery-operated real-time clock. It will need to download current ephemeris data though because the
satellites will have moved significantly from where they were on its last fix.
When your module starts in this mode, with all the rest of your quad's
noisy electrical components, it could take a few minutes for it to get a fix.
The third mode is called the "hot start" and this is when your GPS module has all
the required information from its last fix and that information is still valid. That means the GPS module itself
is within 100 kilometers of where it was previously, and it had its previous fix usually within the past couple of hours.
All right, let's take a look at a few ways we can minimize our time to first
fix of the day for our GPS module. Two of these I'm about to list I'm going
to demonstrate for you here shortly so stay with me. The first way to reduce your GPS module's time to first fix
is by powering up with an unobstructed view of the sky. Do this in as much of an open area as possible. This will give your GPS module
more potential satellites to receive strong signals from. The second way to reduce your GPS module's time to a fix is by eliminating
or reducing the amount of electrical noise it's
experiencing from your other quad's components. It's been known for a while that your quad's components generate noise
that interferes with your GPS module. The Betaflight dev's have discussed this many
times before and at least Pawel Spychalski has made a
video showing how your quad's HD camera can interfere with your GPS
module. There are three ways I can think of to reduce this electrical noise
on your GPS module. First, separate it as much as possible distance-wise from the rest of your quad's components. Of course, this is sort
of hard to do with most quads especially micros. 3d printed GPS mounts
help a little. Another way would be to shield your
noisy components by using copper foil tape and/or aluminum foil. It sounds like a good way, but it's sort of tedious
and impractical for FPV quads. The third way to reduce noise in a GPS module is
to power it on in isolation. This is nothing new, in fact,
catch22mania has a video showing how he does it which iIll link to in the video description below. I'm going to
demonstrate for you a special method which allows you to not only power up
your GPS module in isolation, but keep it powered on without
unplugging it after it's acquired a fix. So, it won't lose that fix while powering
up the rest of your quad. For your GPS module to start up with as
much valid required information as possible, it's going to need some memory.
I'd recommend getting one with flash memory and those usually come
with 4 to 16 megabytes. If not, at least get one with battery backup RAM.
That'll give you on the order of about 32 kilobytes. Your best bet for a fast
lock with your GPS module is to power it up in "hot mode" within two hours of its last fix. If you do this, most likely the
information it has on the satellites which are in its view
during that last fix will still be valid and it can use that information
to get its subsequent lock. Another really good way to minimize time to
first fix is through what's called assisted GNSS.
This is where your GPS module gets its information not only from the satellites,
but also from other sources as well. Your smartphone uses this type of feature.
This is the second special method of reducing your GPS module's time to first
fix that I'm going to demonstrate for you.
First though, I'm going to demonstrate how you can do this isolated power up method and keep it powered on so your GPS module retains its satellite lock. All right, to make our isolated
power supply cable for our GPS receiver, all we're going to
need is a couple wires, a male balance lead connector for your
size lipo that you use for your quad (I use 4s
lipos so I'm using a 4s male balance lead connector). You also
need a 5 volt step down voltage regulator and I
happen to be using the iFlight Micro BEC 5 volt. This is adjustable for a 5 volt or 12 volt output depending upon whether or not these two tiny little pads
are connected. It comes without these pads connected so the default output
voltage is 5 volts which is exactly what we need for our GPS receiver. Links to this 5 volt step down voltage regulator as well as other step down voltage regulators
are available in the video description below. This is the smallest and lightest
one I could find. So these three things right
here that we need to power our GPS receiver come in at a
weight of . . . one gram! Let's go ahead and solder this
stuff up. The wires going to the balance lead
connector are going to be soldered here for our 5 to 36 volt input,
and here. So we're going to stick it on this and we're going to tin
these input pads (5 to 36 volts and ground) and these output pads (ground and 5 volt output) here. Next, we'll tin the wires and the other ends. Then we need to tin this wire
and this wire. That should work. Put the input power lead here and then we're going to put the ground
for it here. We want to make sure that we put these
wires on the correct pins of this connector. So I'm not sure
exactly which pin is supposed to be ground and which pin is
supposed to be positive. So what I'll do is grab this 4s lipo with its balance connector (and you see these two ridges here it
only goes on one way - it goes in those gaps there). So, it goes
on like that which means that this pin over here
is ground. We want to connect the red wire positive lead up top. Ground is going to go down here, positive up there. What I want to do first is put a piece of shrink tube on here so that I can slide it up on that pin after we connect it.
Here we go. I'm going to slide this on here,
move it down. That's on there pretty good. Then we slide the shrink tube up
like that. We do the same thing for the
positive lead. Doesn't matter really what color shrink tube you use.
Tug on a little bit to make sure it's secure. All right, this is the end that's
going to go into our balance lead of our lipo battery. Now before I even
think about connecting my GPS receiver up to this regulator, I
want to make sure that this regulator is working properly and outputting 5 volts. So, what I'm going to do is I'm going to connect the
battery to our brand new connector the proper way
then I'm going to put a black lead (negative) here, positive here and we're getting 5 volts!
So this regulator, this iFlight 5 volt bec step-down voltage regulator,
is working properly. Okay, now just to test this out to make sure it's working properly and before I attempt to connect a GPS receiver that's connected to one of my quadcopters
to this step down voltage regulator, I'm going to use a spare Matek SAM
M8Q GPS receiver. The reason I'm doing that is because
we can tell when it's powered on through one of these red LEDs. When one of these LEDs lights up red, we know that it's got power
and with power it can actually attempt to get a satellite lock. So, all I'm going
to do is take the connector that comes with the GPS
receiver, take the power and ground leads . . . the
yellow wire in this case for the Matek M8Q is going to the rx pad
of the SAM M8Q whereas the blue wire is going to the tx pad (It
goes like this) of the GPS receiver which goes to the rx pad of the flight
controller. Because tx here goes to rx on the flight
controller and rx here goes to the tx on the flight
controller. Anyway, all we're concerned about right now is the power and ground. So I'm going to take power . . . actually let's do ground
first it's easier for me, and power. All right, now the way this is going to
work then is the GPS receiver is going to get
its power from the balance lead of the lipo and these two wires from the rx pad of the gps receiver goes to your
uart tx pad on your flight controller and the tx wire going from the tx pad
of your gps receiver goes to the rx pad of your flight controller uart. So let's
power this up with a lipo balance lead and watch for
one of these LEDs to light up red showing that this is getting power. There you have it! Now, if we set this
next to the window, we should see it get satellite lock.
Let's go ahead and do that! I've got the SAM M8Q receiver along with its isolated
power supply cable sitting next to the window. So, when I
power this up, we should see the red LED come on saying
it's got power and within a short amount of time (since
it's being powered in isolation), we should see it get a satellite lock
fairly quickly. Let's go ahead and power it up. We've got the red light saying it's got
power. Oh! Look at that! Blue light - it's
already got a satellite lock! That's the magic of this isolated power
supply to power up the GPS receiver on its own. Then, since we're using the balance lead of the lipo to power this, we don't have to disconnect the GPS receiver at all.
We just plug in the xt30 connector into our quadcopter and power up the rest of
the components and this should maintain lock. After
we tested out the prototype we cleaned up the wires a little bit and added some shrink wrap. This is what the final product looks like for our
isolated power supply for our GPS receiver. Turned out pretty good! Nice and clean. Very small. Total weight comes in at . . .
2 grams! Nice! All right, that was one of the two special things we can do to
reduce our GPS module's time to first fix and it truly is a game
changer. The second special thing we can do is actually use the assisted GNSS feature to configure our GPS module and
get valuable information from other sources in
addition to the navigation satellites themselves. This method I'm going to show you is good for any GPS module using a
u-blox chipset such as the SAM M8Q or the NEO-M8 series. These chipsets are
available on some of the Beitian GPS modules, Matek modules, and other brands. The type of information available to you will
depend on if your module has flash memory or battery backup RAM.
With flash memory you get more valuable information. For specifics on whether or
not a GPS module has flash memory, look for it in the vendor's product
description and check out the u-blox product summary document for the series
module you're interested in under the u-blox unmanned vehicle page. If you're still uncertain, call or email
the vendor before purchasing it. The u-blox assisted GNSS feature is
called AssistNow and they have a free software
program which you can download called u-center. You just download and install the program to your computer like you would
any other. They even have a user's manual which
walks you through how to use the application. So you just download and install it from this link and this is what your u-blox u-center software application program looks like
initially when you open it up. Now to connect your GPS module receiver
to the u-blox u-center application program,
you'll need to grab one of these types of usb to serial adapters which
you can get on Amazon for like five to ten bucks. I think these came
two for 12 bucks. These are three different types. You don't need all three.
I happen to be using this one just because I ordered different versions and
this one arrived sooner. Then you just connect your GPS receiver
up to the usb to serial adapter using this cable which
I got in the same package as my GPS receiver. This end with the jst connector gets plugged into your GPS module
and these plugs right here get attached to the VCC, ground, tx, and rx.
Of course, tx here goes to rx here and rx on the usb to serial adapter
goes to the tx. The wiring pinout for different GPS modules is not the same, so make sure that you connect it up properly for your particular version of the GPS module. The other end obviously gets plugged into your computer and you're good to go. All right,
once you've got your GPS module connected to your computer,
and in this case I've got my SAM M8Q GPS module connected which only has battery backup RAM, you go to receiver connection and com4.
There are two types of data that you can obtain using u-blox AssistNow. One is called AssistNow Autonomous which is what I'll
be using for this SAM M8Q GPS module
since it only has battery backup RAM. The other one is called AssistNow Offline data (good for flash memory).
I'm not going to get into the specifics
of the differences between AssistNow Autonomous and AssistNow
Offline data. For that I'll refer you to the AssistNow Services Quick Start
Guide and also the u-blox M8 Receiver Description Manual. You can read up on that yourself. Since the SAM M8Q receivers have battery backup RAM, I'm going to enable the AssistNow
Autonomous feature. To do that we go to "View,"
"Message View," "u-blox," "Configuration," "NavX5." We just toggle on this "use AssistNow Autonomous" feature
and click "Send." Then we can go to "Acknowledge" and we see that our message that we just sent has been successful. There's various other things that you
can do with regards to configuring your GPS
module within u-blox's u-center. To accomplish
what we just did with the NavX5 where we enabled
AssistNow Autonomous, I don't believe you need to register
with u-blox for the AssistNow Autonomous feature. You can see over
here my GPS module receiver is now
gathering data from the satellites . . . it's populating the data it's pulling from
the satellites. What the AssistNow Autonomous feature
does is it provides your GPS module with that "boost" or "head start" for its
first fix by extending the valid time frame of
the ephemeris data which it would normally
use up to around three days as opposed to a few hours. Now the other option, AssistNow Offline, wel'l need to register with u-blox to obtain that data. To register for that AssistNow
Offline data, you go to this url and fill out this form. Once you hit "Submit" they'll send you an email and you'll be provided with a
token which is just an alphanumeric designation
which you'll need to input into a field to obtain the AssistNow Offline data
that you want to get. Now, after you've registered and you've connected a GPS module that has flash memory to your computer, you connect as we did before. Then, you go to "Tools" and to get the offline data you go to "AssistNow Offline" and you select the u-blox module
series for your particular GPS module. In my case, it's u-blox 8/u-blox M8. Here's where you would put in your
alphanumeric designation for your token. Then you
select the satellite constellations that you
want the AssistNow Offline (that's what this ANO stands for AssistNow Offline) that you want the AssistNow Offline data for.
In my case, I'm going to select both GPS and Glonass. You can select up to five weeks however, the older the data gets
the less accurate and valid it is. So I would recommend only selecting one week
at a time which is what I'll do here. You can also
select how often you want the data to appear
from one day up to three days. So you can get it for every day, every other day, or every third day. If you select every day you're going to get a lot of data and the file size is going to be bigger. If you select every third day, you're
going to get less data however your file size is going to be
smaller. Because I'm only going to select one week here, I'm going to select every
day. At this point, I'm just going to
click on "Download from server." Here's my 7 days worth of data.
I'm going to select flash based to flash it to my GPS module
and click on "transfer to flash." Here's the progress of it. "Retry zero"
is a good thing. When it's done, it'll show "finished."
"Finished transfer." We press "close," click "ok"
and that's how simple it is. Now my Beitian BN220 GPS module has the AssistNow Offline data stored in its flash memory and it can use that for that extra boost or head start to acquire the satellite
fix in minimal time. Now I'm going to show
you the results of both of those special methods - powering up the GPS module with and without the isolated power supply and also with and without the AssistNow data. This chart is representative of the results I obtained
for both the SAM M8Q GPS module on the left and the Beitian BN220 module on the right. Note that the vertical scales are
different. Your results may vary from mine depending on a whole lot of factors
such as the time of day, operating environment, and your specific
location among other things we've previously gone over.
These are only the type of results I obtained given my situation.
The bars in bright blue depict the amount of time it took for the GPS
modules to obtain their first fixes with the tall bars on the left side of
each of these charts having the GPS module powered on at the
same time as the rest of the quadcopter's
components (and therefore without the isolated power supply). The two bars on the right of each of these charts are with the GPS module
powered on first (using the isolated power supply) before
connecting the lipo xt 30 to the quad. The difference between the two bars on
the left and the ones on the right just go to show you how much of an
effect the interference from the rest of the quad's components can have on your GPS module obtaining a fix. You'll also see I've captured the results for both with and without AssistNow Autonomous data or "ANA" over here for the SAM M8Q on the left, and AssistNow Offline data or "ANO"
data for the BN220 over here on the right. The light blue bars represent a self-imposed two-minute time frame
after the GPS module got its fix before I powered up the rest of the quad by
connecting the xt-30. This means I just waited another two
minutes after the fix before I powered up the quad. The reason I did this was because I found out, in my situation,
if I powered up the quad without waiting an additional two minutes,
when I did power up the quad the GPS module would lose its fix
and not recover it. In fact, over here on the left these two little gray bars
you'll see with a SAM M8Q, it actually lost its fix even after I waited those two minutes before powering up the quad
but it did recover it in 19 seconds over here (which is
0.32 minutes) and in about 8 seconds (or 0.13 minutes) over here. My takeaway from these results is this - the biggest improvement in
time-to-first fix occurs when you use the isolated power
supply for the GPS module and you'll save a little bit more time
by using the AssistNow data. By using both,
you could be flying in about two and a half minutes as depicted over here on
the right, or if you didn't use either, you could
still be waiting around for the GPS module to get its first fix. So those are some of the ways to get a
faster fix with your GPS module. My favorite is with the isolated power
supply. What's yours? Let me know in the comment section below and I'll see you next video. 'Till then, thanks for your time and clear skies friend!
