In this post I will present you everything you need to build an autonomous quadcopter, since the project's translation is taking a lot of time.
Firstly a cross-like frame is required. You can create your own wooden or metallic frame, or you can buy one , for example : http://store.diydrones.com/3DR_ArduCopter_Quad_C_Frame_Kit_p/kt-ac3dr-01.htm . The frame should be lightweight and strong.
Then you will need 4 motors and 2 pairs of propellers (each pair is consisted from a pusher and a puller propeller). We used 4 Brushless DC outrunner motors from scorpion (http://www.scorpionsystem.com/) which are not available anymore. Feel free to find your own, just make sure that all combined they can pull the estimated weight of the quadcopter. Also your propellers should fit in your motors. For example these propellers fit that motor .
After deciding which motors fit you, you should search for 4 ESCs (Electronic Speed Controllers). We decided to leave a fair electrical current margin between the ESC and the motor, just in case of a really large current spike. That means that if our motor had a max continuous current value of 20 Amps, we would buy an ESC of 35 Amps.
The electronic speed controllers produce PWM outputs for the 3 phases of each motor, when they receive an input signal from a source. This source will be our microprocessor. The microprocessor will receive signals (either analog or digital) from various sensors and after deciding what must be done after, it will produce signals for the ESCs. You can buy a microprocessor you are familiar with and program it, we chose to buy an Arduino Uno because it is supported with a really large number of sensors and shields and it is really easy to use it and learn it. For other autonomous vehicles (Hexacopters etc) you may use Uno's brother , Arduino Mega .
Then you will need sensors. We built our quadcopter using a single 3 axis gyroscope board, a GPS module, a compass module and a single 3 axis accelerometer board at the beginning ,but we faced a lot of problems with the interface and data collection, so we switched to ArduPilot to solve everything. Though if I would build a new quadcopter again I would give a try to this IMU combined with a GPS module and a compass module.
Finally,you will need a source to supply your motors and the electronics components. We bought a LiPo battery and it is really up to you which one you will buy. Of course, the higher the mAh the better! just make sure your battery has the cells that the motor requires. Also consider buying this battery to supply your arduino (that is, if you chose to built it with an arduino!) so that you will leave the LiPo to do the "heavy work" (supplying the motors). This way you can gain some more minutes of flying for your quadcopter.
