10 SERVO 08.2016
It is important that you place the vehicle on a sturdy, flat,
and level surface. I used a table, but made sure it was
actually level first with a carpenter’s level. It may be time to
pull out scraps of cardboard and paper to level things.
When you’re ready, click the “Calculate” button. After a
few seconds, the process will complete and the sensors are
calibrated.
Now, it’s time to set up the ESCs. You did remove the
propellers, right? It’s hard to tell which direction the motors
are turning without propellers, so I put a flag of masking
tape on each motor shaft to make it easy to see which
direction the motors are spinning. Carefully read the seven
step procedure that we will use to calibrate the controllers,
and then check the three confirmation check boxes when
you have complied (Figure 4).
The next screens will guide you through finding the
neutral rate for each controller. I recommend you do this
for each motor individually, as they could be slightly
different and it takes very little time. You will click the start
button and slowly advance the slider until the motor just
starts spinning. Click stop, and then move to the next
motor.
While doing this, it is vital that you confirm that the
motor is indeed spinning in the correct direction as shown
on the diagram (pay special attention to the vehicle-forward
direction so things are not backwards). If your motor is
spinning in the wrong direction, pick two of the three wires
going from the ESC to the motor and reverse them. (Any
two.) I did this on the ESC end since those connections
were the easiest to change. I was lucky and only had to
change one out of four. For what it’s worth, my neutral
rate time constant was around 1,117 µs (Figure 5).
The control loops that determine how the vehicle will
react to differences in where it is versus where we want it
to be must be tuned. The tuning for every quad is different
and can determine if you have a steady and slow
photography platform or a hot-rod racing machine that is
responsive to the slightest touch of the controls. For now,
select the “Current Tuning” option.
In a future article, we will discuss how to tune any
drone for better performance. This will use the default
values in the firmware that are perfectly adequate to get in
the air.
On the next screen, click “save” to write the
configuration we’ve just set up to the flight controller’s
Figure 5. Calibrating each motor just takes a few minutes.
Make sure the motors turn in the correct direction as
shown in the diagram. If they turn in the wrong direction,
just reverse any two of the three power wires to that
motor.
Figure 4. Carefully read the ESC calibration procedure and
then verify you have done each of the three essential steps
to begin. Don’t just check the boxes, double-check your
work! Then, check the box.
OpenPilot and LibrePilot
When researching different flight controllers and
flight controller software before doing this build, I
found a lot of references and even hardware stamped
with the OpenPilot name. The OpenPilot website was
down, though, and the forums inaccessible. I also saw
references to LibrePilot that had software which
looked very similar and supported the same
hardware.
Turns out that in June 2015, there was a rift in the
OpenPilot community. Many of the core developers
made a fork of the project called LibrePilot with the
idea to be open to all contributors and governed by a
board of members keeping a steady course for the
project.
The LibrePilot website and documentation are still
a work in progress, but should be considered as the
source for all official information and downloads of
the software.
