DIY Drone
Guide
The following document is a brief do it yourself guide
for building a multi-copter flying done.
It is based on a significant amount of experience and careful
consideration. Many of the suggestions
are also useful for other types of drones including boats. In this guide I've tried to provide detailed
information and specific advice to help with design and ordering of components. This will help the builder get started
quickly.
A great source for drone information (hardware,
software, reviews, etc.) is rcgroups:
http://www.rcgroups.com/forums/index.php
YouTube also has a lot of drone related information
(reviews, tutorials, etc.)
https://www.youtube.com/watch?v=XOH9kGXyWsg
http://www.rcgroups.com/forums/showthread.php?t=1710948
https://www.youtube.com/results?search_query=DIY+drone
Other sources:
http://www.instructables.com/id/DIY-Drones/
https://www.facebook.com/DIYDrones/
Safety guidelines
This section is not intended to be a definitive list
of safety precautions for drones. It’s
only meant to point out some of the main issues with drone safety.
Multi-copters can be dangerous depending on its size
and power. A Syma X5C could hurt your
fingers or eyes. A larger drone is like
an upside-down flying lawnmower and should be treated with care. It can also cause a lot of damage if it lands
on somebodies head from a significant height.
You should be careful of your fingers and wear eye protection when using
your multi-copter. It’s also possible
that your drone could get out of control and fly directly at someone (including
yourself) which could injure head, body, or fingers (if they try to fight off
the incoming drone). A shield, net, or
perhaps cut resistant gloves is recommended to protect against that scenario.
You should always
unplug the multi-copter battery before touching other parts of the
drone. This is especially important
after a crash when emotions run high and you might forget. Don’t just use the on-off switch since cheap
on-off switches have been known to malfunction.
Always turn on the transmitter before plugging in the multi-copter
battery. A drone without a transmitter
can easily get out of control. You
should also remove the propellers when first testing a drone after new
modifications (e.g. new electronics, software, etc.). Li-poly batteries can also be dangerous. See the battery section for details.
Ready to Fly
Drones
Before building your own drone you should consider
buying a ready to fly drone and modifying (i.e. hacking) it. This option can save money (especially when
considering the likelihood of crashes) and also achieve good performance. The following drones are currently the best
for modification in my opinion. They can be purchased from various online vendors
(see the section on vendors).
Note that the transmitter and receivers for
inexpensive ready to fly drones are not very good. It’s easy to go out of range or lose control
of the drone. It’s also not possible to
combine them with a separate microcontroller for additional functionality. Therefore, the transmitter, receiver, and
other electronics in a ready to fly drone should normally be discarded and
replaced with more general higher quality components. Recommendations and suggestions are made in
the following sections.
Syma X5C
- very stable, easy to fly,
and easy to modify
- weighs about 100g
- has 155g total lift (i.e. it has 55g excess/net lift
after overcoming gravity)
Note that a drone should ideally have total lift of at
least twice the weight. Racing and
acrobatic drones can have lift of four times the weight or more.
Note that the total lift reduces as the battery
voltage decreases during operation. A
lipoly batter typically starts around 4 V and reduces to 3.5 V.
https://learn.sparkfun.com/tutorials/battery-technologies/lithium-polymer
Syma X5C-1 Drone, Your Mother Could Fly This!
Quadcopter 101
https://www.youtube.com/watch?v=y93vzA-KRlM
Note that the Syma X5C can be bought without the
transmitter and camera for about half the price.
It’s also possible to buy a Syma X5C in parts. For example,
http://www.banggood.com/Syma-X5-X5C-Motor-Base-Spare-Part-4PCS-p-978463.html
http://www.banggood.com/Syma-X5-X5C-Clockwise-Motor-Spare-Part-X508-p-928804.html
http://www.banggood.com/Syma-X5-X5C-Anticlockwise-Motor-Spare-Part-X507-p-928806.html
http://www.banggood.com/Syma-X5-X5C-Main-Blades-Propellers-Spare-Part-X502-p-926874.html
In this case you could design your own frame and use
the Syma X5C motors and motor holder / gears to make your own drone design (hexacopter, etc.).
JJRC H8C
http://www.banggood.com/JJRC-H8C-2_4G-4CH-6-Axis-RC-Quadcopter-Without-Camera-RTF-p-957758.html
This drone was designed to be the “Syma X5C
killer”. JJRC is my favourite drone
maker because they try so many different designs and a lot of them work
well. The H8C is a like a X5C on nitro. It has larger motors (8.5 mm diameter vs 7 mm
diameter), a battery with twice the voltage (7.4V), and a stronger frame and
gears. It weighs about 145g and it has a
total lift of 275g, so it has much more net lift and power than the X5C. The drawback is that the 7.4V is too much for
the motors (their nominal voltage is 4.5V) to handle long term if you fly the
H8C too aggressively. This can result in early motor burn out (hence all the
complaints on rcgroups). However, the
H8C seems to work fine as long as you don’t fly it too hard and the replacement
motors only cost $2.5. The H8C is
currently my favourite low cost drone due to the extra power and extra room in
the fuselage (useful for putting in new electronics).
Note it’s also possible to upgrade the Syma X5C motors
(7mm diameter) to motors (8.5mm diameter) to get a lot more power. However,
the 7.4V battery from the H8C is required to get the full benefit. Note that you also need electronics capable
of handling the extra voltage – you can’t just attach a 7.4V battery to a X5C
board. The X5C motor holders also have
to be enlarged using a circular file to accommodate the larger diameter
motors. However, enlarged versions can
be purchased separately here (note these versions don’t come with the gears):
http://www.banggood.com/JJRC-H5C-New-version-Motor-Mount-Motor-Base-p-977610.html
MJX X101
The MJX X101 is very stable and easy to fly. It’s a good large size inexpensive drone
weighing about 400g and it can easily lift 600g-800g. It’s suitable for sport flying or carrying
large cameras such as a GoPro. I prefer this model to alternatives such as
the Tarantula X6 (sportier with less load capability and less reliable motors)
and the Syma X8C (heavier and less sporty).
However, the stock transmitter and receiver should immediately be
replaced (along with the flight controller) since it is known to have fly away
problems due to loss of communication even at close range.
MJX R/C - X101 - Review and Flight Flyin' Ryan RC
https://www.youtube.com/watch?v=zkA0S-u5pIE
The Syma X8C is also a pretty good option in this size
category. I have an orange (great
colour) X8C and I’m very impressed with its quality and simple layout. It has a lot more room in the fuselage than
the X101 for putting in custom electronics.
Spare parts are also very easy and inexpensive to obtain. The drawback is it’s noticeably heavier than
the X101 so it’s less sporty, but it has more load carrying capacity and a
longer flight time. The X8C is a great
low cost camera drone because it’s a very stable flyer. You can attach a GoPro or similar components
to it.
Components of
a Flying Drone
The main components of a flying drone are:
Frame
Motors
Gears
Propeller blades
Landing gear
Motor amplifiers
Battery, charger, and regulator
Transmitter and receiver
Flight controller
Optional components:
Blade protectors
Microcontroller
Sensors
Actuators
Wireless communication
Data logging
First person view (FPV)
A brief description of each item with advice and
specific suggestions is given below.
Frame
A good frame is light, strong (to survive crashes),
and rigid (to reduce vibrations). The
arms need to be long enough to separate the propellers and thin enough not to
interfere with the air flow. The
distribution of weight and number of motors / arms can also affect a drones
handling, stability, and carrying capacity so it needs to be carefully
considered / optimized. Often vibration
isolating materials such as rubber are incorporated into the connection points
for the flight controller board and camera to reduce the effects of vibrations.
A frame is typically constructed from wood (Poplar,
Birch, etc.), foam, plastic (3D printing), carbon fiber composite (very popular
with racing drones), or metal (for large drones). A mix of materials (e.g. plastic for the
fuselage and metal for the arms) is also possible. Some of these materials can also be used to
reinforce an existing ready to fly drone frame.
The weak point is typically the thinnest part of the arm near the
thrusters.
http://aeroquad.com/showwiki.php?title=Frame-Materials
Note that carbon fiber is a conductor of electricity,
so precautions should be taken with exposed electronics so they don't short
circuit when touching carbon fiber frames.
Carbon fiber can also interfere with wireless communication.
Foam or wood / sticks might be good options for
prototyping. Note that the landing gear can be integrated into the bottom of
the frame with the motor mounts / protectors.
Frames kits can also be purchased (make sure to order spare arms), for
example
http://www.readymaderc.com/store/index.php?main_page=product_info&cPath=76_606&products_id=5004
-- this is one of the best most indestructible carbon fiber frames.
Note the uni-body construction. Uni-body construction is stronger but more
difficult to repair.
http://www.hobbyking.com/hobbyking/store/__85257__Diatone_ET_200_Class_Micro_Multirotor.html
-- lightest carbon fiber frame available for micro quads
http://dragonplate.com/
-- vendor of carbon fiber composite stock
http://www.bphobbies.com/view.asp?id=V870830
– vendor of carbon fiber composite stock
http://www.hobbyking.com/hobbyking/store/__1770__1756__Multi_Rotors_Drones_Parts-Carbon_Fiber_Tube.html
-- inexpensive carbon fiber tubes which provide a very good option for making
custom light weight frames
Motors
Brushed DC motors are the most inexpensive option for
drones and they can provide very good performance. They are the best option for a first done in
my opinion. However, brushed motors
normally wear out after about 6-10 hours of operation. They can also wear out if they get overheated
due to insufficient resting time between battery changes or when a propeller
gets stuck (which spikes the current and temperature). Here are some good sources / selections for
brushed DC motors for small / medium sized drones:
https://micro-motor-warehouse.com/collections/all-motors
- dark edition motors have the most thrust for an 8.5
mm diameter motor.
- they also sell inexpensive pinions
Hubsan X4 FPV & Camera Plus Motor Set (4pk) (model
H107D+-03)
http://www.robotshop.com/ca/en/hubsan-x4-fpv--camera-plus-motor-set-4pk.html
- 8.5mm diameter motors suitable for upgrading the
Syma X5C (without pinions)
- the pinion can be taken from an X5C though
Hubsan X4 Plus Motor Set (4pk) (model H107P-07)
http://www.robotshop.com/ca/en/hubsan-x4-plus-motor-set-4pk.html
- 7mm diameter replacement motors for Syma X5C
(without pinions)
Holy Stone Original Motors for F181 RC Quadcopter
Spare Parts
- 8.5mm diameter motor suitable for upgrading a Syma
X5C -- check the pinion size compatibility though
https://www.amazon.ca/gp/product/B00Y84PH3Y/ref=ox_sc_act_title_7?smid=A3QTILSGJZUURE&psc=1
http://www.gearbest.com/rc-quadcopter-parts/pp_294256.html
- larger brushed replacement motors for the MJX X101
Note that the stock 7mm diameter motor of the Syma X5C
produces about 40g of thrust when combined with the stock gears and
propellers. The regular 8.5mm diameter
motors above produce 55 g of thrust (with the Syma X5C propellers / gears) with
3.7V batteries and a whopping 97g with 7.4V batteries. However, the 7.4V level should only be
applied for short durations (like nitro) or you will owe somebody a 10 second
drone. Note that the motor holders of
the Syma X5C need to be enlarged in order to fit the 8.5 mm diameter motors
(see the Ready to Fly Drone section for details).
The JJRC H8C thrusters produce 70 g of thrust with
their 8.5 mm diameter motors. This is
somewhat lower than the 97 g produced with the upgraded X5C. The reason is not clear, but it’s likely due
to a different gear ratio, propeller, or motor.
I suspect that JJRC detuned their motors to make them more reliable.
Brushless motors use electrical commutation instead of
mechanical (brushed) commutation. Their
performance is higher because brush wear is not a factor thus allowing them to
run faster and cooler. This leads to
higher efficiency and reliability. The
bearings tend to wear out before the motor windings and they should be
regularly lubricated. However, brushless
motors are significantly more expensive than brushed motors, especially when
considering the extra cost of the electronic speed controllers required (see
the Amplifier section for details).
Therefore, brushless motors are typically used for more expensive and
larger drones. Due to the high power,
propeller speeds, and cost involved I don’t recommend brushless motors for a
first drone.
The DYS BE1806-2300kv and EMAX MT1806 2280kv are two of
the best options for larger sized drones in the 250 size class (250 mm diagonal
length). They typically provide 300-500g of thrust per motor (depending on
battery voltage and propeller size). The
best vendors for brushless motors are Hobbyking and Banggood. Note that brushless motors are also sold in
economical combo packs with matching speed controllers and propellers. For example,
http://www.hobbyking.com/hobbyking/store/uh_viewitem.asp?idproduct=86550
The EMAX Quad MT2204 2300kv is also a very good motor
with similar capabilities to the motors above.
I like EMAX motors because they come in CW and CCW
versions and don’t require special propeller adapters.
Note that it's normally a good idea to quickly get
your hands on some motors from a scrap pile or from a North American vendor
(see the links above) while you wait for motors from international online
vendors to arrive. Note that motors and
blades are sometimes combined to make ducted fans (see the Blade Protector
section below).
Gears
Gears are often preferred to no gears (direct drive)
in order to reduce the speed of the propellers and provide more torque (and
less motor wear). This allows more
efficient operation with more lift capability (larger propellers). It can also make the drone easier to control
and less noisy. Nylon gears are most
common for small/medium size drones and metal for larger drones. Sometimes the gear materials are mixed such
as metal for the pinion and nylon for the large gear which provides a good
trade-off between strength (metal) and noise (nylon). 3D printed gears are an interesting and
flexible option for making gears if they can be made strong enough. Many of my favorite ready to fly drones use
gears, so I suspect they result in more optimal designs at least for brushed DC
motors.
Gears, motor holders, and propellers can be bought in
part kits for various ready to fly drones.
For example:
http://www.banggood.com/Syma-X5-X5C-Motor-Base-Spare-Part-4PCS-p-978463.html?cur_warehouse=CN
- Syma X5C motor holders (includes gears)
Add a 7mm / 8.5 mm diameter motor with a propeller and
you have a great inexpensive drone thruster.
These mounts are sized for 7mm motors so they have to be enlarged for
8.5 mm motors with a circular file.
Motor mounts for 8.5 mm diameter motors can also be purchased in the
following link. This option is less
painful than enlarging a motor mount in my opinion.
http://www.banggood.com/JJRC-H5C-New-version-Motor-Mount-Motor-Base-p-977610.html
-- this motor mount comes without gears (need to take them from the 7 mm motor
mounts above)
It should also be noted that the propeller/gear
bearings of some drones can be upgraded to provide better performance and
longer motor life. The JJRC H8C for
example has these nice upgrades. They
work very well in my drone.
Propeller blades
Propellers come in many different shapes and
sizes. Selecting the optimal shape and
size is an interesting design problem, especially when considering the motor /
gears capability and the optimal efficiency range of the motor. The selection of optimal components is often
determined using a thrust testing stand such as:
http://www.hobbyking.com/hobbyking/store/uh_viewitem.asp?idproduct=84687
Note that half the blades must rotate CW and the other
half CCW in a quad rotor (same direction along the diagonals with the CW
diagonal leaning to the right) in order to balance out the torque in the yaw
direction. The motor / fastener
(adaptor) for the propeller should also be specifically selected for either CW
or CCW rotation so propeller doesn't become loose during operation. Propellors also are
constructed from different materials such as plastic and carbon fiber
composite. I prefer soft plastic propellors for beginners since they are much safer for
fingers. Carbon fiber is similar to aluminum
from the fingers perspective.
Propellers can be obtained locally from Robotshop,
Hobbyking, and other online vendors. For
example,
http://www.hobbyking.com/hobbyking/store/__1233__501__Multi_Rotors_Drones_Parts-Propellers.html
Electric ducted fans (EDF) are sometimes used instead
of exposed propellers in order to provide the better protection for blades (and
your fingers). For example:
Air Hogs Helix X4 Stunt
http://www.airhogs.com/site/product/helix-x4-stunt
EDFs are not quite as light/efficient though for small
thrusters but they are more compact. They are also easy to pivot with servos
for thrust vectoring purposes. EDFs can
also be used to propel boats and cars.
Hobbyking is one of the best sources for EDFs. For example,
http://www.hobbyking.com/hobbyking/store/__17145__EDF35_with_11000kv_Motor_Assembled.html
http://www.hobbyking.com/hobbyking/store/__682__681__Hardware_Accessories-EDF_Units_With_Motor.html
The best source for EDFs is probably
http://www.aeorc.cn/products/motor/edf-upgraded-plus-version.html
Blade protectors
One purpose of blade protectors is to protect the propellors during a crash. However, they are probably more
important for protecting the motors and the gears. During a crash the propeller typically locks
in place which results in a stall condition for the motor and a very high
current (the back EMF drops to zero when the motor stops turning). This high current will quickly overheat the
motor and the amplifier electronics normally resulting in permanent
damage. Therefore, a drone should be
powered down (or disarmed) immediately after a crash if possible, especially if
it doesn’t have blade protectors. The
disadvantage of blade protectors is added weight, but more importantly a
reduction of thruster efficiency due to the extra drag.
Landing gear
Sometimes landing gear are not needed if they can be
combined with the frame / motor mounts.
For example, the landing gear can be removed from the Syma X5C and the
motor mounts can then be used as the landing gear. It’s also sometimes beneficial to make the
gear deliberately weak so they absorb more of the impact during a crash. This can be accomplished by attaching the
landing gear with weak glue, using foam landing gear, etc.
Motor amplifiers
A flight controller / microcontroller needs an
amplifier in order to drive the motors.
It can’t be connected directly because the motor requires more voltage
and current than the microcontroller can provide (normally only 5V and 10 mA). This is analogous to a CD / MP3 player
requiring a stereo amplifier in order to drive speakers.
Motor amplifiers are normally called electronic speed
controllers (ESC) in the hobby community.
ESCs for brushless motors are more expensive than brushed ESCs because
they are more complicated (they normally employ a microcontroller). Note ESCs for flying drones / aircraft are
not reversible (i.e. they don't run backwards) although they may have some form
of braking capability. Car and boat ESCs
are reversible, but they are larger and heavier. For brushed DC motors simple
inexpensive N-channel MOSFET circuits can be used since only non-reversible
operation is required. For example:
http://bildr.org/2012/03/rfp30n06le-arduino/
http://www.digikey.ca/product-search/en?keywords=FQP30N06L
http://users.encs.concordia.ca/~bwgordon/DIY_brushed_ESC.pdf
- how to build an inexpensive DIY ESC for brushed DC motors
http://users.encs.concordia.ca/~bwgordon/DIY_brushed_ESC_new.pdf
- new version of the DIY ESC which is a bit easier to wire if you can get the
Freetronics MOSFET board
Both guides also discuss in detail how to select the
wire size and type for the ESCs / motors.
Brushless ESCs are normally purchased. Some of the better models include
http://www.hobbyking.com/hobbyking/store/__81793__DYS_16Amp_Micro_Opto_BLHeli_Multi_Rotor_Electronic_Speed_Controller_BLHeli_Firmware_SN16A.html
http://www.hobbyking.com/hobbyking/store/__81794__DYS_20Amp_Micro_Opto_BLHeli_Multi_Rotor_Electronic_Speed_Controller_BLHeli_Firmware_SN20A.html
http://www.hobbyking.com/hobbyking/store/__87851__ZTW_Spider_Series_18A_OPTO_Multi_Rotor_ESC_2_4S_BLHeli_SimonK_Firmware_.html
– one of the lightest for this capacity
DYS is one of the better brands especially for light
weight ESCs. EMAX, ZTW, and Hobbyking
are also good. I tend to prefer lighter
ESCs if possible. For reference, the DIY
brushed ESCs weigh about 2-3g with similar current capacity (4g with
wires). Note that the wires also have
significant weight depending on their size.
Note that ESCs often have a battery elimination circuit (BEC) which
provides a regulated 5V for sensitive electronic devices such as a flight
controller or receiver.
Note that you normally want to select an ESC that has
somewhat more current capability (e.g. 50% more) than your motors require for a
given battery voltage. Otherwise your
ESCs will overheat unless you restrict the motor commands in the flight
controller software.
On a side note, it’s also possible to reprogram
certain models of non-reversible brushless ESCs (such as the Hobbyking blue
series) to behave as reversible brushed ESCs.
This might be useful if you want a light weight reversible brushed ESC
for robotics applications or if you want to land your drone on the
ceiling. For example,
http://www.hobbyking.com/hobbyking/store/__2164__TURNIGY_Plush_30amp_Speed_Controller_w_BEC.html
http://www.hobbyking.com/hobbyking/store/__27195__Atmel_Atmega_Socket_Firmware_Flashing_Tool.html
– required to change the ESC software
http://www.hobbyking.com/hobbyking/store/__27990__USBasp_AVR_Programming_Device_for_ATMEL_Processors.html
– required to change the ESC software
https://www.youtube.com/watch?v=051ga6xaOhs
– how to reprogram
https://www.youtube.com/watch?v=uYHoc34phh4
– how to reprogram
http://robowars.org/forum/viewtopic.php?t=1581
Battery, charger, and regulator
Lithium polymer (lipoly)
batteries are normally used since they are lighter for a given energy storage
than most other batteries. However, they
can spontaneously catch on fire, so safety precautions should be used
especially with larger batteries (>750 mAh).
When charging they should never be left unattended and they should be
stored in a safe fireproof place (e.g. a strong closed metal toolbox). Furthermore, you should be careful not to
short (or even get close) the battery leads since a large current will be
produced which can result in a harmful flash and very high temperatures (like
an arc welder). When soldering / working
with the leads of a lipoly battery you should always
put electrical tape on one lead to prevent an accidental short circuit.
Note that the energy of a lipoly
battery is proportional to weight, so there is a trade-off between flying time
and battery weight. The flying time can
be used to estimate the average current for the motors using the conservation
of energy as follows.
E(battery) = E(motors)
Vb * mAh =
4 * Vm * I * t(discharge time in h) – assuming 4 motors
I = ( Vb / Vm ) * ( mAh / t )
/ 4
where Vb is the battery voltage and Vm
is the average motor voltage. Assuming Vb/Vm = 3 (a conservative estimate)
gives the average current I in mA
I = 3 / 4 * mAh / t
For example, the MJX X101 has a 7.4V 1200 mAh battery
and the flight time is 9 min. Therefore,
an estimate of the average current for each motor is given by
I = 3 / 4 * 1200 / (9/60) = 6000 mA
This information can be used to select wire and
amplifier sizes for the motors.
Note in some special cases (such as the JJRC H8C with
the double sized battery voltage) the Vb/Vm ration could be 6 or more, so the
above formula should be adjusted in those special cases. The Vb/Vm ratio of 3 is a reasonable approximation
for most stock setups. If you need more
accurate estimates of the current you can measure it in the lab with the
propeller attached, preferably in a thrust testing stand.
Note that the total lift reduces as the battery
voltage decreases during operation. A lipoly batter typically starts around 4 V and reduces to
3.5 V.
https://learn.sparkfun.com/tutorials/battery-technologies/lithium-polymer
This information should be taken account when
selecting battery and motor sizes and perhaps in the flight controller. At the least, a battery monitor should be
employed to indicate when the battery level is too low. A battery monitor can be constructed using an
Arduino ADC or bought as a separate component such as:
http://www.hobbyking.com/hobbyking/store/__14520__HobbyKing_8482_Lipoly_Battery_Monitor_1S.html
http://www.hobbyking.com/hobbyking/store/uh_viewitem.asp?idproduct=7224
Here is a good inexpensive source of batteries /
chargers for Syma X5C size drones (650mAh -- an upgrade over the stock 500mAh):
Holy Stone 5-In-1 Max 2.5A Current Input Fast Battery
Charger and two batteries for X5C Holy Stone M68
https://www.amazon.ca/gp/product/B00RSWH0K6/ref=ox_sc_act_title_1?smid=A3QTILSGJZUURE&psc=1
The largest and highest performing battery that can
fit inside a Syma X5C is:
Turnigy nano-tech 750mah 1S 35~70C Lipo Pack (Fits
Nine Eagles Solo-Pro 180)
http://www.hobbyking.com/hobbyking/store/uh_viewitem.asp?idproduct=20386
This can provide 10-12 min with the stock Syma X5C
configuration without the camera. Note that the connector of the Turnigy
nanotech 750 must be reversed (if it hasn't been done so already by someone
else) after it has been bought as the connector polarity is the opposite of
what the Syma X5C (and Syma X5C battery chargers expect).
https://www.youtube.com/watch?v=avwobYJ_AeA
The double voltage (7.4V) battery that is the secret
sauce of the JJRC H8C increased power is given here
http://www.banggood.com/JJRC-H8C-RC-Quadcopter-Spare-Part-Battery-H8C-10-p-953564.html
http://www.gearbest.com/rc-quadcopters-parts/pp_182606.html?wid=21
Lipoly battery voltage levels decrease
significantly over time during operation (20-30%). Furthermore, when motors / amplifiers are
connected to batteries they cause significant electrical noise at the battery
leads. A regulator circuit (or a
separate battery) is thus required, in order to provide a constant and less
noisy voltage, for sensitive equipment such as flight controllers, micro
controllers, and receivers to insure stable operation. The stability of electronic components such
as Xbee transmitter / receivers also seems very sensitive to battery voltage
even though it is typically provided by a regulator on the microcontroller
board. Some electronic speed controllers (ESCs) have a battery elimination
circuit (BEC) which provides regulated power for sensitive equipment. Note that step-up and step-down regulators
are also available along with adjustable regulators that can do either
task. Here are some examples of good regulators
circuits:
http://www.robotshop.com/ca/en/5v-step-up-voltage-regulator-u3v12f5.html
http://www.robotshop.com/ca/en/33v-step-up-voltage-regulator-ncp1402.html
http://www.robotshop.com/ca/en/step-up-step-down-voltage-regulator-s7v7f5.html
- does both automatically (good if you want to use different battery types, eg 3.7V and 7.4V)
Alternatives:
https://www.sparkfun.com/products/317
http://www.digikey.ca/product-detail/en/on-semiconductor/MC34063AP1G/MC34063AP1GOS-ND/919067
http://www.digikey.ca/product-detail/en/texas-instruments/MC34063AP/296-17766-5-ND/717432
Transmitter and receiver
A transmitter / receiver combination is used to
manually guide your drone with a control stick input. These systems normally use the 2.4 GHz band
that many wireless devices use (WiFi, Xbee -- see below, etc.). The 2.4 GHz is free for companies to use and
thus very crowded. For this reason you
need to be careful about interference from all nearby 2.4 GHz devices including
transmitter / receivers for other drones.
Carbon fiber composite frames can also interfere with wireless
communication as well as poor placement / selection of antenna.
Most transmitters / receivers from different companies
are not compatible. I've heard Flysky
and Turnigy are compatible though. A new
standard called DSMX from Spektrum has been introduced which is more resistant
to interference. If you want to run
several drones in close proximity then it's best to use a DSMX transmitter /
receiver. Note mode 2 transmitters (or
adjustable mode) are best for quad rotors. Good inexpensive DSMX transmitters
include:
Spektrum DXe Transmitter System with AR610 Receiver
http://www.robotshop.com/ca/en/spektrum-dxe-transmitter-system-with-ar610-receiver.html
DX6i 6CH DSMX Radio System with AR610 Receiver
http://www.robotshop.com/ca/en/dx6i-6-channel-dsmx-radio-system-receiver.html
Good inexpensive DSMX receivers include:
Lemon Rx DSMX Compatible 6-Channel Receiver
http://www.lemon-rx.com/shop/index.php?route=product/product&path=72&product_id=122
OrangeRx R615X DSM2/DSMX Compatible 6Ch 2.4GHz
Receiver w/CPPM
Good inexpensive non-DSMX transmitter / receivers
include:
FS-I6 Flysky i6 2.4 GHz Receiver and Transmitter Kit
Turnigy 6X FHSS 2.4ghz Transmitter and Receiver (Mode
2)
Note that the receiver board produces a pulse for each
channel with a duration proportional to the stick position. This information could be used by a
microcontroller board in addition to the flight controller.
The control sticks also adjust potentiometers inside
the transmitter box. The voltage from
these pots can be read with an Arduino ADC pin.
Furthermore, a DAC signal (or filtered PWM signal) can be fed into the
transmitter (replacing the voltages from the potentiometers) in order to
externally control the drone from an Arduino / PC.
You should also be careful of the "fly away"
problem when flying outdoors that some drones have when they go out of
range. The phenomena is pretty
self-explanatory. It can be emotionally
scaring for drone owners. A good
controller will try to come home or land when it's outside of range. A drone builder should try to include this
feature.
Flight controller
A flight controller is a microcontroller board with
control software for drones (quad-copter, tri-copter, hexa-copter, etc.) and a
built in inertial measurement unit (IMU) to sense orientation and
acceleration. A set of PID controllers
use this sensor information to command the motor actuators in order to obtain
stable motion with respect to a reference position. Commands from the transmitter are read by the
controller and used as the desired / reference position for the drone. The PID parameters can be adjusted and tuned
using configuration software. Flight
controllers simplify drone development considerably since you don't have to
write control software or buy and connect an IMU. This gives more time to focus on the overall
mechatronic and design problems. Note
that the flight controller must be firmly connected (perhaps with vibration
isolation mounts) to the frame in order to accurately sense the drone position
and orientation.
There are a variety of flight controller boards and
software packages available from the hobby community (Naze32 / Cleanflight,
CD3D / Openpilot, Ardupilot / APM, etc.).
In my opinion, MultiWii is best for DIY projects for engineers because
it's Arduino compatible and inexpensive while also supporting a large variety
of controller boards. The main advantage
of the other boards / software is 32-bit processors (MultiWii uses 8-bit
Arduino processors) which provide more power and memory. However, the power and memory are not needed
for PID control so the extra capability is not very useful for control
purposes. An additional microcontroller
(8-bit or 32-bit) can be added for more computing power and additional
functionality without being bogged down by low level flight control operations.
The alternatives to MultiWii are also supposedly
easier to use. However, MultiWii is much
easier to use if you want to change the flight control software because the
program structure is less complicated with less lines of code. It’s also Arduino based so it provides a very
familiar architecture and programming environment. Basically, MultiWii software designers kept it
simple because MultiWii boards have less memory. Therefore, MultiWii is actually easier to use
in many significant ways. More
information about MultiWii including how to configure the software is provided
here. Note this is a preliminary guide
and provided on an “as is” basis – don’t ask me any question yet.
http://users.encs.concordia.ca/~bwgordon/MultiWii.html
Some of the better MultiWii boards include:
http://www.robotshop.com/ca/en/mwc-multiwii-flight-controller-uav-w--pins-arduino-compatible.html
Robotshop also has a version with soldered pins but I
prefer to solder the pins separately since it provides more mounting
flexibility in tight spaces (i.e. the pins can be mounted in different
directions). Note that many of the pins
don’t have to be soldered – see the MultiWii guide above.
http://www.readytoflyquads.com/flip-mwc-flight-controller
- same as Robotshop model above but for less money
http://www.readytoflyquads.com/flip-2-5
- adds barometer (for altitude measurement) and a compass
This is my preferred board at the moment. The compass allows the control of the
yaw/heading and the barometer allows rough control of the altitude. The other boards above just stabilize the
drone position and orientation. However,
this is enough to do many things including aerobatic maneuvers.
CRIUS MWC MultiWii SE V2.6
- Crius seems to be one of the largest producers of
MultiWii boards
- pins are soldered in the board (can be removed if
necessary)
CRIUS All IN ONE PRO Flight Controller V2.0
- MultiWii board with the most memory and inputs /
outputs (based on Arduino Mega microcontroller)
Optional components:
Microcontroller
Adding an additional microcontroller to your drone (in
addition to the flight controller) can be used to add new functionality to your
drone without burdening (or potentially damaging) the flight controller or
modifying its software. Additional functionality
includes tasks such as path planning (using GPS or other sensors), reacting to
stimulus (fire, light, etc.), wireless communication with a PC, etc. I strongly recommend using a microcontroller
if you want to add additional programmable features to your drone -- don't use
the flight controller for anything except flight control. For flying drones, low weight microcontroller
boards with low power consumption are recommended such as:
1) Iteaduino Arduino Nano (Arduino compatible)
http://www.robotshop.com/ca/en/iteaduino-nano-arduino-compatible-microcontroller.html
https://www.itead.cc/iteaduino-nano.html
I recommend this one over other clones since Itead is
a good brand name and the USB interface / driver is good (it won't suddenly
stop functioning like other clones).
Note that this board is classified as an "Arduino Pro or Pro
Mini" in the Arduino IDE and not a "Nano" -- this is the case
for most Arduino Nano clones.
2) Teensy 3.2 (Arduino compatible)
This is a 32-bit microcontroller board with much
greater processing power and more memory than an Arduino (10-20x). It is 100% Arduino compatible after you
install the Arduino IDE add-on (Teensyduino).
It also has 16-bit ADC (Arduino has 10-bit) and 12-bit DAC (Arduino has
none). This is a great board for
mechatronics and audio projects in general.
The main drawback is it takes a bit more power (50 mA at 5V) than a
regular Arduino board (25 mA at 5V) but not that much.
http://www.robotshop.com/ca/en/teensy-32-usb-microcontroller-development-board-pins.html
3) Raspberry pi 3
The 64-bit Raspberry Pi 3 is a single board computer
that is significantly heavier than the microcontrollers above (45 g). It can, however, be used with large flying
drones and ground / water drones. It has
much more processing power than the options above -- 20x or more times the
processing power of a Teensy 3.2. This
makes it suitable for more demanding tasks such as computer vision and complex
path planning / decision making algorithms.
However, the Raspberry Pi 3 uses significantly more power (580 mA at 5V)
and it’s more expensive. The Raspberry
Pi 3 is comparable in processing power to an inexpensive laptop from a few
years ago. It can add a great deal of
intelligence / autonomy to a drone. It
runs a variation of the Linux operating system which is very good for embedded
/ real-time programming.
http://www.robotshop.com/ca/en/raspberry-pi-3-computer-board.html
https://www.raspberrypi.org/magpi/raspberry-pi-3-specs-benchmarks/
Sensors
Various sensors can be used to give your drone the
ability to sense and react to its environment.
This includes:
ultrasonic - good for inexpensively measuring
distances, obstacle avoidance, and the height above ground (for altitude
control near the ground). For example,
HC-SR04 Ultrasonic Range Finder (iTead Studio)
http://www.robotshop.com/ca/en/hc-sr04-ultrasonic-range-finder.html
Note that sensors such as ultrasonic and light sensors
(below) can be mounted on servos in order to point and measure distance in
different directions. You can
potentially create a map to guide the motion of a drone this way.
Infrared / light - good for measuring distances and
finding hot objects. For example,
http://www.robotshop.com/ca/en/infrared-light-sensors.html
http://www.robotshop.com/ca/en/electronic-brick-light-sensor.html
- measures incoming light, easy to hook up
http://www.robotshop.com/ca/en/mini-photocell-light-sensor.html
- same as above and lighter, but requires a bit more wiring (need to add resistors)
http://www.robotshop.com/ca/en/sharp-gp2y0a02yk0f-ir-range-sensor.html
– IR range finding sensor
http://www.robotshop.com/ca/en/sharp-gp2y0a710k0f-ir-range-sensor.html
-- range finding sensor for long distances
Inertial measurement unit (IMU)
Measures orientation, acceleration, and sometimes
pressure/altitude. Note that the flight controller board has a built in IMU to
control stability. However, a good
external IMU can potentially be more accurate and provide better
performance. For example,
BNO055 9 DOF Absolute Orientation IMU Fusion Breakout
Board
This board is good because it has built in filtering
software to compute Euler angles, etc.
You and the microcontroller don't have to waste time with matrices,
transformations, and filters to use it.
http://www.robotshop.com/ca/en/bno055-9-dof-absolute-orientation-imu-fusion-breakout-board.html
GPS sensors
Can be used outdoors to measure the position to within
2.5m. This allows the drone to hover in
the same location or follow a path which is useful for camera applications.
Example GPS boards include:
http://www.robotshop.com/ca/en/adafruit-ultimate-gps-breakout-66-channel-mtk3339.html
http://www.robotshop.com/ca/en/sfe-venus-gps-w-sma-connector.html
http://www.readytoflyquads.com/rtf-econo-line-gps-w-mounting-backplane-and-compass
http://www.readytoflyquads.com/mini-ublox-m8n-gps-w-35x35mm-mounting-backplane-and-compass
Actuators
Additional actuators (apart from the thruster motors)
can be added for additional functionality.
This includes servos for picking up and pointing at things, for example:
http://www.robotshop.com/ca/en/hitec-hs55-servo-motor.html
-- a good lightweight servo
Interfacing an Arduino to servo motor is covered in
the following lab:
http://users.encs.concordia.ca/~bwgordon/arduino_lab2.html
Servos can also be potentially used for changing the
direction of your thrusters for thrust vectoring capability.
and lasers for shooting at things, for example (there
are cheaper and lighter lasers available elsewhere though):
http://www.robotshop.com/ca/en/laser-module-red-point.html
Wireless communication
Wireless communication between a microcontroller and a
PC can be used for remote control of the drone from a PC and telemetry (sending
data back to the PC for analysis). The
most simple (and one of the best) ways to communicate wirelessly is using a
pair of Xbee communication modules. One
module connects to the serial port of the microcontroller and another module
connects to a USB adapter that connected to the PC. The PC can then perform two way communication
(at 250 kbps max) with the microcontroller using standard serial communication
protocol software (examples are provided in the microcontroller section). Note it's normally better to use the series 1
Xbee (not the series 2 or pro) since it's much easier to configure and it has
less communication delay (about 1/30s).
Here are the components needed for an Xbee link:
http://www.robotshop.com/ca/en/1mw-xbee-transceiver-module-trace-antenna.html
-- need two of these, one for each side
http://www.robotshop.com/ca/en/sfe-xbee-explorer-usb.html
The Xbee pro can be used for longer distances. When using Xbee communication (which is also
2.4 GHz based) you should check for delays, dropped / lost messages, and
interference (with transmitter / receivers, WiFi, etc. ).
Note that the raspberry pi 3 has built in WiFi which
allows communication with a PC at a much faster rate than the Xbee (an antenna
might be required for long distances though).
Data logging
Recording flight data is good for analyzing the cause
of crashes as well as providing data for analysis and plotting. However, most microcontrollers such as
Arduino have very small amounts of memory for recording data. Therefore, the data needs to be sent back to
a PC with wireless communication such as Xbee or
recorded on a micro SD card. The micro
SD option is less complicated with better performance so that’s what I normally
recommend. The following micro SD
adapters can be used with an Arduino or other microcontroller board. The SD Datalogger
example in the Arduino IDE shows how this is done.
http://www.robotshop.com/ca/en/microsd-adapter-arduino.html
http://www.robotshop.com/ca/en/adafruit-microsd-card-breakout-board.html
First person view (FPV)
First person view equipment sends a live image back to
a screen or goggles which can be used to fly a drone from a first person
perspective. This cool feature adds a
new level of realism and interest to drone flying and racing. FPV requires a camera mounted on the front of
the drone which can also be pointed using servos. The camera is then connected to a transmitter
which sends a live video feed back to a receiver which then connects to a
monitor or goggles. Since the 2.4 GHz
wireless band is pretty crowded most FPV equipment uses the 5.8 GHz band. The quality of the video is a bit low (600
horizontal lines) so an additional high definition recording camera (which
records to a micro SD card) is often added to larger drones. The following links provide recommendations
for entry level FPV gear based on my experience. I have a set of Cyclops goggles and they are
very good.
FPV gear
Quanum Cyclops FPV Goggle and receiver
Quanum ELITE QE58-2 5.8GHz Selectable
25mW - 200mW Wireless AV Transmitter
Aomway 5.8GHz 4-Leaf Clover Antenna Set
for TX/RX
RunCam SKYPLUS-L28-P FPV Camera PAL
http://www.hobbyking.com/hobbyking/store/__88662__RunCam_SKYPLUS_L28_P_FPV_Camera_PAL.html
Recording cameras
RunCam FULL HD 1080P 120 degree FPV
CAMERA (DC 5V)
RunCam2 FULL HD 1440P 4MP 120 Degree FPV Camera w/
WiFi (Orange)
The RunCam2 can also be used as a FPV camera in
addition to recording.