issue. This only took about 15 minutes
and I was back in business.
First, connect the ground side
radio to the computer. After any
necessary drivers install (I tested this
on both my Mac and a SurfacePro
running Windows 10), the OP-Link
icon becomes active. Click this icon
and read over the options to configure
the radio. The main thing we need
here is the device ID to tell the flight
controller. Write this number down.
We also have to tell the ground
side radio that it will coordinate
communications by clicking the
“Coordinator” checkbox. Set the
maximum output power of the radio
to 100 and set the min/max channel
settings to match your country’s band
plan. In the US, we can leave these
settings as 0 and 250, respectively
(Figure 8). Save the settings to the
setup and disconnect the ground side
radio.
Next, connect the air side radio
(the flight controller) to the computer.
Again, when the OP-Link icon
becomes active, click it to enter the
radio settings. This time, we make sure that Coordinator is
not checked. Enter the ground side radio’s device ID into the
coordinator text box. Again, set the max power to 100 and
the min/max channel settings to meet with your country’s
regulatory standards.
Now comes the fun part: testing it out! Disconnect the
flight controller and reconnect the ground side radio. I
placed my quad back out on the patio and powered it from
the flight battery. This time, the long USB cable is not
necessary. In a few moments, the radios will bind and you
should see the RX indicator on the LibrePilot GCS go very
high, as well as see the binding in the OP-Link panel.
Returning to the control panel, you should see the
indicators update if you change the orientation of the quad.
We now have wireless telemetry!
I zip tied the antenna to the GPS mast to keep it out of
the way (Figure 9). Another excellent solution would be to
design a part to be 3D printed. We may do that in the
future, but for now I don’t know exactly where the antenna
is best placed and I want to be able to easily swap out the
entire flight control system to be able to test other products.
I did a few flights to test the telemetry link. I found
that the range was not very good. It seemed that if the
aircraft was more than about 30 feet away, it would not
maintain a reliable telemetry stream. Some ground testing
confirmed this. It looks like I have one of two issues: 1) a
second damaged radio; or 2) a flight controller or receiver
with non-genuine and poor
performing parts. It is hard to know
which is which now, but many OP-Link users have videos of telemetry
working at ranges of many hundreds
of meters. I’m going to be on the
LibrePilot forums and try to figure out
exactly why my system seems to have
a limited range, and try a different
set of transmitting hardware.
GPS Stabilized
Modes
With a GPS onboard, we have
nine new flight modes to explore
( https://librepilot.atlassian.
net/wiki/ display/LPDOC/GPS+
Flight+modes). The most interesting
of these to me are position hold
mode, return to base, and path
planner modes. Position hold mode
keeps the quad in place regardless of
the winds and environment (within
reason). Return to base mode will
cause the quad to fly back to its
home location and hover. The path
planner mode allows the quad to
autonomously fly a predefined flight path.
To use the GPS modes, we need to change the way the
quad calculates its attitude (orientation and position in
space) and set up the flight mode switch on our transmitter
and flight controller. First, connect your flight controller or
ground side radio to the computer. In the configuration tab
of the GCS, click on the Attitude settings on the left side of
the screen. In the settings tab, there is a drop-down menu
labeled “Attitude Estimation Algorithm.” We have been
using the “Basic (Complimentary)” estimation algorithm,
but need to change this to “GPS Navigation (INS13).” Once
that is done, save the settings.
Next, we need to set up the flight mode switch on our
handheld transmitter to control how the quad will fly. We
did not set this up when we first went through the
transmitter configuration wizard. To do this, we need to set
a “Pitch Curve.” This is a non-intuitive process, so you can
follow along with the text and a helpful You Tube video I
found as well ( https://youtu.be/6n_5wNA2j TI).
Press the menu button on the handheld transmitter
and go into the settings page. Go down to the “PIT/CV”
item and select it. By default, the pitch curve has a linear
relation to the throttle control for all three positions of the
flight mode switch. With the flight mode switch in the top
(normal) position, set all five numbers on the curve to 0%.
Next, move the flight controller switch to the middle
position (ID1) and set all of the values to ~50%. Finally,
SERVO 09.2016 35
Figure 9. After making
sure the GPS cable
would reach the flight
controller, I mounted
the GPS mast and zip
tied the telemetry
antenna to it.