Drone / Copter Building
Reversing Motors
The motors used on Drones / Copters are 3 Phase Brushless Motors. And
because of this you cannot just reverse direction in you software.
That's not to say some Speed Controllers are not
reversible (they make them) but the majority of
Drone Speed Controllers are not. To reverse motor direction just
reverse any 2 wires going into the motor. It doesn't make a difference
which one.
Forward
Reverse
Position
123
213
1
231 132
2
312 321
3
Pulse Width Modulation (PWM)
Why are motors controlled via PWM? For two reason; low-end torque and
noise immunity. The way PWM works is to vary the duty cycle of a
pulse. For a slow motor response you send a short pulse, for a faster
response you send a longer pulse. Full-on would be an 100% duty cycle
(more or less depending on the ESC type). Keep in mind, for
bidirectional ESCs a 50% duty cycle would be motor stop, with 0% and 100%
being the polar extremes (but don't worry about directional right now).
In a nut shell, if you were to send a small voltage to a motor at stall it
probably wouldn't move (bearing stick, friction, etc.). However, if you were
to throw full power at a 5% duty cycle the motor would quickly respond and
then slow on the off part of the cycle. If you have a Function
Generator try hooking up an ESC to a motor. Set the frequency from
anywhere between 0.25 - 10KHz with a 0 to 5v pulse.
Battery Elimination Circuit (BEC, UBEC and/or SBEC)
A BEC is nothing more than a glorified 5volt regulator. The 'U' in
UBEC stands for Universal and the 'S' in SBEC stands for Switched.
They're all the same thing. Do you need them? No. Is it
better to use them? Yes. The electronics environment on a Drones
is very noisy (electrically). These circuits help eliminate the noise
and stabilize the voltages.
Electronic Speed Controllers (ESC)
ESCs are used to sequence the 3 phase control voltages to the motors.
They are controlled by the Pulse Width Modulated (PWM) signal sent from the
uController board. Warning: the manufacturers of most Drone types of
ESCs play a little trick on you. The 3-wire PWM control cable which
connects your uController to the ESC not only sends PWM signals to the ESC
but also sends back a 5v bias back from an on-board BEC. This means if
you have 4 motors & ESCs you'll have 4 supplies pushing 5v back into your
uController board. You should cut the Red lead from each PWM cable
coming from the ESC. However, if your uController board does not
supply 5V you should keep at least one PWM cable intact.
Drone Flight Time Calculator - A
simple program to calculate the flight time, battery capacity, and payload.
More Coming...
Blade Arrangements
Basic Quadcopter Wiring
Interesting/Helpful Links
Drones, UAVs
Scientific American - What is a Drone?
DJI Quadcopters - Copters, Parts
APM ArduPilot - Open source autopilot
Endurance R/C - Electronics,
Parts
HobbyKing - Forums,
Blogs
Fat Shark - Copters,
Parts, Electronics
Spektrum - Transmitters, Recievers
Blade - Copter, Parts
