9

LENS

have the mounting points ready-drilled for the range
of motors you are likely to use with it, and will
have an acceptable physical size range as part of
its specification.
Motor speed is expressed as a KV value, which
denotes the rpm speed increase they deliver per
volt. The KV should be matched to the propeller
size, for example, our craft with its relatively large 8”
propellers has 1000KV motors, while a racing frame
with much smaller propellers might have a KV value
of well over 2000.

WITH GREAT POWER COMES MOTION
Finally, the voltage and current figures of the motor
define what motor controller and battery choices you
should make. The voltage is often expressed in terms
of battery pack size, as well as voltage, for example
our motors are expressed as 2S-4S, meaning a lithium
polymer battery with between 2 and 4 cells in series.
There should also be a peak current figure that will be
necessary when picking a speed controller.
The motor controller will be a small PCB with three
sets of connections. There will be the three motor
terminals, either large solder pads or wires, two
battery input wires, and a
control cable terminated
in a plug designed for the
PWM output of a flight
controller, or radio control
receiver. It contains a
small microcontroller and
the power transistors to
control the motor. There
are motor controllers that
will run a motor in both
directions, but those you are likely to encounter will
be unidirectional. Since half your motors must rotate
in the opposite direction to the others, you will need
to wire them for reverse operation by reversing two
of the three motor wires. The firmware used on the
vast majority of motor controllers you will encounter
is called BLHeli, and you will find controllers with
either 8-bit or 32-bit processors. The important figures
on a motor controller are the battery voltage, again
expressed in terms of the number of cells, and the
peak current it can handle. Both these figures should
match their equivalents on your choice of motor.
All of your motors should be the same model, and
all should be driven by the same model of controller.
For this reason, both motors and controllers are often
sold in packs of four. You will also see 4-in-1 controller
boards that incorporate all four controllers, these are

designed for builds in which space and weight are at

a premium, but have the disadvantage that, should

you damage one of the controllers, you will have

destroyed all four in a stroke. We bought a pack of

four BLHeli 32-bit controllers, each with a rating of

2S-4S, and a peak current of 30A.

Below

One of the motor

controllers from

our build

MOTOR SPEED IS EXPRESSED AS

A KV VALUE, WHICH DENOTES

THE RPM SPEED INCREASE THEY

DELIVER PER VOLT

Here are the parts we used, but this is just a

guide. You’ll need equivalents to the parts here,

but there’s no need to restrict yourself to these

parts. There’s a phenomenal range of choice in

the parts you use and the best bit about making

your own drone is that you can pick the add-ons

that are best for you. Well, that and the fact that

you’ll know exactly how to fix it if (when?) you

crash it and break something.

• 1 × 450 mm PCB quadcopter frame kit


• 4 × Racerstar BR2212 1000KV 2-4S
  brushless motors


• 2 × 8045 carbon nylon propeller kits


• 4 × Racerstar Tattoo 30A 2-4S brushless
  motor controllers


• 1 × BF3.2 Omnibus F4 V2.1 ST 32 F4
  flight controller


• 1 × XT60 male plug 12AWG 10 cm with wire


• 1 × 1800 mAH 75C 4S LiPo battery, with
  XT60 plug


• 1 × FlySky i6 FS-i6 RC transmitter


• 1 × FlySky FS-A8S RC receiver

PARTS LIST

• 2 × 220 mm battery tie-down strap for
  RC drone


• 1 × 1 m 12 AWG silicone wire SR Wire1


• 3 × screws


• 3 × stand-offs
  We strongly recommend getting several
  sets of rotors as they’re easy to break. Getting
  more than one battery will mean that you can
  keep flying while one is charging.
  This is just for the basic drone. Once you’ve
  got experience flying it, you might decide that
  you want to augment it with more bits and
  bobs. A camera is probably the most popular
  extra feature, and they range from cheap, tiny
  sensors with low resolution, to professional-
  quality cameras. You will need to make sure
  that you’ve got a way of transmitting and
  receiving the camera feed. A gimbal will allow
  you to control the direction of the camera
  while the drone is flying, but it’s hard to control
  both drone and camera at the same time.
  Make sure you get a second person to help
  control the craft.