Continuing on from Droning on and on and on…, my interest in octocopters was piqued by the article, Police drone can be hacked with $40 kit, says researcher, as they were using 900 MHz XBees. I tried to find the actual octocopter that the researcher had used, which are being employed by the Dutch Police, but a quick google only came up with a few options, that used XBees. These are listed in the Octocopters using XBee section below.
For a look at a commercial octocopter, see ASCTEC FALCON 8.
Comparing 3, 4, 6, 8 and 12 blades
An interesting comparison of Tricopters, Quadcopters, Hexacopters, Octocopters and Decacopters can be read at Quadcopter vs Hexacopter vs Octocopter: The Pros and Cons, or Hexacopters, Quadcopters and Octocopters – What is the Difference? Simply put, as the number of blades increases, so the cost, weight, payload capacity, speed, stability and safety (rotor redundancy) increases, however – battery life decreases (down to 10 minutes for some octocopters).
- Quad: These models are inexpensive and less durable. Perfect for beginners and non-professionals. No engine out capability – if a motor fails, the drone drops.
- Hexa: The ideal choice for semi-professionals or hobbyists that want a very durable, steady-flying copter that can carry heavier weights. Up to two motor out capability.
- Octo: The top of the line. These are copters that have a high price tag, but they are powerful, stable and fast. Advanced functionality and stabilization features make an octocopter a must-have for professionals. Up to 3 or 4 motor out capability.
Comparing structural designs
Amongst the many possible designs, Lineal, Radial and Coaxial are the most popular (see Quad vs Hexa vs Octo -copter. (Radial and coaxial) Advantages-Disadvantages?):
- Lineal designs have two rows of motors, one on each side of the center, so a linear hexacopter would have three rotors on each side. Likewise a linear octopod would have four rotors on each side, and a dodecacopter would have six on each side. Also, known as H-type.
- Radial designs have the motors positional radially, that is their positions describe a circle.
- Coaxial designs will have two rotors on each arm, so a coaxial octocopter will have four arms, with two blades on each. However, they can be noisier, have a greater inertia (so that they are hard to disturb, but if disturbed then the flight controller has a harder job at re-establishing stability). NOTE: They can be considered inefficient (15% – 20% (this is debatable – see note below)), when compared to flat radial design, due to a reduced amount of “clean air” available, as the rotors are stacked on top of each other. The inefficiency of the coaxial designs is not necessarily true:
This loss is because the 2 propellers are not correctly matched.
The ease of assembling 2 motors upside down without being able to trim the propellers planes distance and without “tuning” the diameters/pitches is the reason of this loss.
A well-conceived contra-rotative setup transforms efficiently the tangential force in axial force (da gud thrust). And yield a gain, not a loss.
This is indeed true with propeller for hovering (low air speed), where more of the mechanical energy is transformed in tangential force.
Gains in the 6% to 18% has been measured (not in RC, real aircraft, larger Reynolds number, though).
This is a noisier setup, generating more sound in the treble.
Before the jet engine era, widespreading, this is where shrouding came in, to reduce this noise while adding some more thrust “by design”.
Additional data on radial (flat) versus coaxial (stacked) rotors:
A coaxial tricopter is called a Y6 for convenience, (a coaxial quadcopter is called an X8) and has motor failure redundancy where as a flat six does not.
There are some redundancy with a flat six but not enough to really be safe to land the machine with one motor out. Especially with a heavy payload on board.
With a coaxial double stack motor you will not even notice a motor out sometimes. All you see is a slight twitch and the controller will take over and keep the machine flying.
Y6 have lots of advantages: it allows a bigger field of view (use of fish eye), take less space to transport, better recognition of the front during flight.
The stability comes with length of the arms and surface covered by propellers. On an Y6 you divide by 2 the surface covered. You can use bigger props to compensate a little (and gain in efficiency and less vibrations)
First: a flat config is more stable: right for 2 reasons: The stability is mainly given by two parameters:
- size of the arm
- surface covered by props.
In a second way you also have the air flow disturbance.
The longer your arms are the better. However, be careful: the longer they are the lower the yaw is effective, you must find a good compromise between size, prop weight and yaw)
The more the surface covered by prop is, the better you will be stabilised. be careful too: increasing the pitch of the prop reduces efficiency but it increases stability in wind.
- Y-type are generally tricopters, but can be used for quadcopters, or hexacopters.
- U-type for hexacopters or octocopters.
- V-type, similar to H, but the sides are not parallel, but with less separation at the rear than the front.
- Cross for octocopters, with two rotors (in a line) on each of the four arms.
- Diamond (hexa and octo).
- Diamond (quad) – a radial design, with rotors front and rear, left and right (i.e. N, E, S, W).
- Square (quad), as diamond (quad), still a radial design, but with the rotors at 45°, rather than 90° to the center forward (i.e. NW, NE, SE, SW).
See Mixer Tabellen, for a comprehensive list of designs.
Octocopters using XBee
So, moving up to Octocopters, here are a few tasty specimens:
- Oktokopter 2 Fully Loaded Octocopter UAV – The details are confusing, and it seems like a scam. There seems to be a Mikrokopter and an Oktokopter 2. Note that there are three photos showing, structurally, considerably different octocopter models, two with eight rotors, this one with four “Y” shaped mounting arms:
this one with eight straight arms:
and one with four coaxial rotors, an X8, (presumably the Mikrokopter):
However, here are two, rather confused, specifications:
OktoKopter 2 Fully Loaded Octocopter UAV Models include:
Ready to fly UAV platform
Spectrum DX 7 RC radio
Xbee 900Mhz setup for easy communication
Spectrum satellite receiver and cable extension
Comes fully assembled, configured and with all parameters adjusted
Very comparable to quadrotor (four rotor) helicopters
Camera not included
Payload: up to 1kg
The OktoKopter 2 “Fully Loaded” Octocopter UAV includes the latest multi-rotor technology and comes with everything to start flying right out of the box:
Preassembled FlightCtrl ME v2.1
Brushless controller BL-Ctrl V2.0
Power distribution PCB
MKUSB for PC connection, USB cable included
Frame set with anodized (colored) tubing
Cover to protect electronics
LiPo Battery 4s 5000mAh
EPP1045 propeller and one spair set
Robbe ROXXY 2827-35 brushless motors
All cables and Zip ties
Vibration dampers for FlightCtrl mount
Buy OktoKopter Octocopter MikroKopter
OktoKopter 2 Fully Loaded Octocopter UAV Description:
Preassembled FlightCtrl ME v2.1
Brushless Controller BL-Ctrl V2.0
Power Distribution PCB
MKUSB for PC connection, USB Cable included.
Frame Set with anodized (colored) tubing
Cover to protect electronics
LiPo Battery 4s 6000mAh
EPP1045 propeller and one spair set
Robbe ROXXY 2827-35 Brushless Motors
All Cables and Zip Ties
Vibration Dampers for FlightCtrl mount
Camera not included
Payload: up to 3kg
The OktoKopter 2 Fully Loaded Octocopter UAV includes the latest multi-rotor technology. Therefore, it is delivered to you fully assembled, configured and flown-in and comes with all parameters adjusted. It includes the Mikrokopter tool software and full Xbee 900Mhz setup for easy communication with your computer. The Xbee setup will enable you to receive live flight data on your computer like elevation, position, ESC temperature, battery charge, voltage and much more. Everything you need to start flying right out of the box is included.
Spectrum DX 7 RC Radio
Strap for your DX7
Spectrum Satellite Receiver
Spectrum Satellite Cable Extension
Navi-Ctrl V1.1 (SMD preassembled) for navigational flight
MK GPS (SMD preassembled), coming home and position hold
MK3Mag – Compass Module with ACC, increased flight stability, yaw fix
Recom 5V/1A Switching Voltage, additional power supply
MK HighSightII Nick + Roll Camera Mount with gyro compensation
2 Highspeed Carbon Servos for camera mount gyro compensation
Vibration dampers for camera mount
2 XBee Pro 900 and 2 XBee USB explorers for your wireless communication with your MikroKopter
Lipo Charger / Balancer by Skycharger, cable set included
Weight: 2kg (with 4S 6000mAh Lipo)
- S15: SJeight OctocopterS15: SJeight Octocopter – A rather professional sounding project. with source code available on github. It doesn’t sound as if it is finished though, but some good guidelines nevertheless.
- RB-Inf-02 Eye Droid 8 Rotor Octocopter UAV Camera Platform – A PDF detailing the specifications:
Cells 3-6 ( LiPo)
Maximum Load 25.0A
GPS Module Port
USB Programming Switch
USB Programming Port
16x Microprocessors (2 Propellers)
MicroSD Card Slot
XBee Indicator LEDs for Dout, Din, and RSSI (receive signal strength indicator) 3-axis Digital Magnetometer
6x additional receiver inputs for future expandability
External Bus (details in future release)
Indicator RGB LED
Enhanced noise rejection power circuit
External GPS Module (with 10” extension cable for ease of mounting on craft Micro SD card for high speed data logging
Dimensions 70mm x 70mm x 12.7mm
Powered from BEC Signal Output Fast Pulse Width Modulated (PWM) signal output to accurately control external ESCs
Digital 3-Axis MEMS Gyroscope
Digital 3-Axis Accelerometer
Digital Pressure Sensor
Flight Battery Voltage Level
USB port for software updates
Auto Pitch / Roll Camera
Compensation Display Output
On-Screen Display (OSD) Overlay
Electronic Speed Controllers:
8 ESC included in EYE Droid 8
Continuous Current: 40A
Burst Current: 55A
BEC Mode: Linear BEC 5v / 3A
Works with 2-6 Lipo Cells
Suitable for Canon 5Dmk2 or similar
Weight – 590g with servos and external potentiometers
Roll axes – 70 degrees total with 35 degrees each side with 10 turn potentiometer
Tilt axes – 180 degrees with external potentiometer
Gear ratio – two options 2.5:1 and 4:1 available Standard gimbal supplied with belt driven tilt axes
Camera tray – 191mm wide
Internal height – adjustable from 130mm min to 180mm
LiPo Flight Battery:
4-cell 14.8 volts
True 120C rating
5C fast charge capable
Built with genuine 12awg Deans Ultra wire
137mm x 45mm x 35mm,
LiPo Battery Charger:
Charges two packs at once
Charge 1-7 Lipo, 1-7 Up to 20 amp per battery charge rate
1000W max charge output (500W per port)
10.5-29V DC only
Includes built-in Dataport and USB cable
Includes two Integrated LBA Balancers
Includes two Hyperion and Align/JST-XH 2S-7S Multi-Adapters
Charge only mode (SOLO or SYNC)
Balance Charge mode (SOLO or SYNC)
Balance only mode (SOLO or SYNC)
Discharge mode( 40W per port w/ 5A max current)
DSM2/DSMX Modulation 2.4GHz
Model Memory: 30
Modes: Selectable 1,2,3 or 4
Telemetry Download module for battery level sends signals to the hand held transmitter.
Secondary remote antenna installed to improve signal reception
4 propellers Clockwise,
4 propellers Counter Clockwise, and
one spare pair
12” diameter x 3.8” pitch
Incorporates high-end optical engine with glass optics and polarized backlights to deliver unparalleled image quality
Quality tooling, radical rubber eye cups, comfortable ergonomics a hard carrying case
The goggles incorporate a 5.8Ghz receiver, matched to a 5.8Ghz 100mAh transmitter located on the EYE-Droid
The goggles are powered by a battery in the head strap and can be charged with the main flight battery charger