FIGURE 8. ESC motor
FIGURE 9. Antenna orientation and transceiver mounting.
about whether it supplies power to
Next, I connected the ESCs to the
motors using 3. 5 mm bullet
connectors as in Figure 8. Note that
the wires aren't yet secured to the
frame because I haven't verified the
proper direction of rotation for each
motor. That comes later, when power
is applied to the system. I also labeled
each arm of the drone by channel
number on the ArduPilot and by
direction of prop rotation.
For example, the ESC driving the
motor in Figure 8 is connected to the
third channel on the autopilot board,
and the prop spins clockwise (CW).
The labeling helps when you're
reassembling a quadcopter after a
crash in the field. If you happen to
reverse a prop, then odds are the
quadcopter won't make it more than
a foot or two above the ground
before it takes a dive.
Because the Q450 frame has
limited ground clearance, mounting
the onboard 900 MHz antenna
vertically for omni-directional
coverage wasn't an option. Instead, I
mounted the unit under one of the
arms, nestled as close to the main
body as possible (refer to Figures 9
and 10). If you decide to follow this
example, then nudge the ESC on the
opposite arm a few cm away from
the body. This will help bring the
quadcopter back into balance.
Setup and Testing
FIGURE 10. Close-up of
With the mechanical build out of
the way, the next step is to connect
the ArduPilot to a PC running the
freely available Mission Planner
software, using the mini USB port.
The 5 VDC from the PC's USB port
won't power the ESCs or motors —
for that, you'll need a battery or
power supply. I prefer the latter,
because I can quickly disconnect the
power and monitor the current drain.
See Figure 11 for my setup.
Notice that the propellers are not
attached at this time. You're going to
be starting and stopping the board,
60 SERVO 11.2012