Watch it in 720p
You need some pre-requisite skills:
- How to use Arduino, enough to get started
- Soldering, wiring, basic electronic skills
- Basic hand tool operation
When one rotor spins faster than the rotor on the opposing side, the faster side will have more lift, and thus the helicopter will tilt. When the helicopter is tilted, the air is being blown slightly sideways instead of directly down, and the helicopter will move.
The propellers also need to be in counter-rotating pairs, two spin clockwise and two spin counter-clockwise. This way, the helicopter does not spin on the vertical axis since the rotational enertia is cancelled out. But when the pair that's spinning in one direction is faster than the other pair, the helicopter will spin on the vertical axis. This is how the helicopter controls its direction.
We will be building a flight controller circuit that contains an accelerometer and gyroscope sensor so that a microcontroller can detect undesired changes in the helicopter's angle, and adjust each rotor's speed accordingly to counter the variation. This microcontroller will do this hundreds of times per second, keeping the helicopter stable in the air.
The flight controller is a completely open source circuit. The circuit schematic and PCB files are provided. The flight controller is completely Arduino compatible. The source code is a modified version of AeroQuad (open source Arduino based quadrocopter control code). The flight characteristics can be adjusted using AeroQuad's configurator utility.
Attached is a diagram that shows you the direction of spin for each motor, remember this diagram! You won't be able to fly if your setup does not follow this diagram.
This microcontroller will also take input from a RC radio receiver, so you can control the helicopter from the ground using a RC radio transmitter.
This helicopter will use four brushless motors. Each motor will be controlled by an ESC (Electronic Speed Controller). The ESCs will be controlled by the microcontroller.
A lithium polymer battery will power the entire contraption.
Summary of Downloads:
- Over 100 pictures in all the steps
- Step 9 contains flight controller circuit and PCB files
- Step 10 contains bootloader and core for microcontroller
- Step 12, 13, 14 contains demo Arduino sketches
- Step 26 contains the flight control software
Step 1: Parts
You need 4 channels minimum but I am begging you to get one with 6 channels. Also get one that uses 2.4 GHz technology if you can. Turnigy has a 9 channel model that is actually very inexpensive, and it runs on an AVR microcontroller that you can put custom firmware on. Personally, I have a old $25 radio that uses 75 MHz FM but I've converted it into a 2.4 GHz radio using a conversion kit.
Four brushless outrunner motors are needed. I used hexTronics 20-22L (this number represents the diameter and coil winding configuration of the motor, there's also a kv value that relates speed and power, higher kv = more
Four brushless motor electronic speed controllers (ESC) are needed. One that is rated for 18 amps is enough. I have heard good things about the Turnigy Plush ESCs because they support high update frequencies (more frequent adjustments means more stable flight). I got the HobbyKing brand clones of the Turnigy Plush ESCs because they are cheaper.
Some ESCs are "card programmable", meaning you can change their configuration using a cheap ($6) programming card, which is really convenient. Buy the programming card that is compatible with the ESCs you've chosen. I got the Turnigy ESC programming card because they are compatible with my ESCs.
You'll obviously need a battery. You will use a 3S1P lithium polymer battery that is rated at least 20C (this is the discharge rating). 3S means 3 cells in series, 1P means one set in parallel. This will give you a combined 11.1 volts. I suggest a 2500 mAH capacity battery (or more). A general rule of thumb is doubling the capacity of the battery means 50% increase in flight time (due to the extra weight).
More info on batteries here: http://www.rcgroups.com/forums/showpost.php?p=1315199&postcount=1
Make sure you pay attention to the type of connector that comes attached to your battery. You're going to need to get the matching connector. I've personally built my entire helicopter using bullet connectors. 4.0mm bullet connectors for the battery and 3.5mm bullet connectors for everything else (the motors come with 3.5mm bullet connectors). (You can get other connectors such as XT-60 connectors, just watch your polarities, also note that all my pictures show bullet connectors)
You need a lot of heat-shrink tubing to act as insulation when using the 3.5mm bullet connectors. Get different colours so you can tell which wire is which.
You need 12 gauge stranded core wire. It must be 12 gauge or thicker to handle the current. It must be stranded core so that it is flexible. Get different colours so you know which wire is which polarity. The best wire is fine stranded copper wire with silicon insulation, but this is expensive.
Get a good battery charger, it must be able to balance and charge multi-cell lithium polymer batteries. I have one of these Turnigy chargers that have many settings, a LCD, and cooling fan, very nice. I also use a laptop power brick to power the charger since an ordinary wall adapter won't be able to handle the current required.
Get a battery monitor so you know when your battery is low. A lithium battery will become permanently damaged if you drain it below a certain threshold. Having a monitor will prevent you from damaging your battery. I have one of these that reports the status of each cell.
The quadcopter's frame I use is this one from HobbyKing. For $15, you get every part you need, plus every screw and nut you need. In comparison, a stick of aluminum would cost me $10 from Home Depot, which is not economical in comparison. I suggest you buy several frames so you have plenty of spare "arms" if you crash (plus plenty of spare screws and nuts).
The propellers must be in counter-rotating pairs (a "pusher" and a "puller"). I use 10x4.7 APC slow-fly propellers. 10 indicates diameter in inches and 4.7 indicates pitch. Larger diameter means more lift but requires more powerful motors. 10 inches is about right for the frame size I am using.
You'll need a entire flight controller circuit (meaning another entire bill of material), I will talk about this in detail later. Meanwhile, you'll need a USB-to-serial cable (FTDI cable) and an AVR programmer.
Plenty of servo cables are required to connect stuff. A minimum of 6 female-to-female cables is required for the 6 channels from the RC radio receiver to the flight controller.
Velcro tape and double sided velcro strapping will be useful as a lightweight way of mounting things and strapping in the battery.
Get a bubble/spirite level (like this one) to help with sensor calibration.
Make sure you get plenty of extras, stock pile on wire, cables, connectors, heat-shrink tubing, electrical tape, glue, screws, etc.