LiPo battery charger, a Spektrum
DX6i, six-channel R/C unit, and a
handful of tie wraps from my
existing inventory.
It's a significant investment if
you're starting from ground zero,
but don't give in to the urge to
skimp on the R/C unit. Saving a
few dollars up front won't make
you feel any better when you see
your quadcopter dash over the
horizon out of control because the
R/C system failed.
The entire frame build time
was about an hour, with half of
that time devoted to mounting the
ArduPilot to the lower platform of
the Q450 (see Figure 5). Frame
vibration is always a concern when
using an autopilot because it adds
noise to the sensors. My
workaround is to first mount the
board onto a soft plastic platform
using nylon bolts and silicon
vibration-damping washers. Then, I
put that combination on a 1/4 inch
layer of foam which I tie wrap to
the frame. The combination
provides a soft cushioned ride at
minimum weight expense.
After connecting the motors to
the ESCs, I wired in the ArduPilot, as
shown in Figure 6. Note the black
square of gaffer's tape on the right
side of the board in the figure.
There is a small square of cloth
between it and the surface of the
barometric pressure sensor. This
'bandaid' of sorts allows the
barometric pressure sensor to
operate free from the effects of the
air rushing by. This is a non-issue on
quadcopters in which the autopilot
board is shielded by a windproof
canopy.
Figure 6 shows the ESCs
connected directly to the ArduPilot.
That is, the board is being supplied
by four 5 VDC supplies in parallel.
To minimize the possibility of a
ground loop, you can cut the power wire (red) on three of
the four ESCs, or non-destructively remove the center
power pin from three of the four ESC connectors.
An alternative approach is to use a pin extractor to
remove the power wire from three short servo extension
FIGURE 6. Wiring the output to the ESCs (left) and the input
from the radio receiver (right).
FIGURE 7. Use a pin extractor on three
short servo extension cables to limit the
possibility of a ground loop from
multiple 5 VDC supplies in parallel.
cables (see Figure 7), leaving one ESC to provide the
ArduPilot with 5 VDC. There's a bit of a weight penalty
associated with using the extension cables but when you
rip an ESC to shreds in a crash, it's much easier to replace
the ESC with one on hand if you don't have to worry
SERVO 11.2012 59
