Choosing the the right sensors for the quadcopter orientation in space.

A quick search on Google show me that there are several sensors that can be used to orientate the quadcopter in space. The list of sensors that can be used, consists of accelerometers, gyroscopes and compasses.
A device that includes accelerometers and gyroscopes is named IMU (Inertial Measurement Unit). This device use one or more accelerometers to detect the acceleration rate and one or more gyroscopes to detect changes in the rotational attributes like pitch, roll and yaw. A compass is a device that determines the direction of movement in relation to the Earth's magnetic poles. This allows a vehicle to move in a certain direction. It is also possible to use proximity sensors such as infrared or ultrasound to guide the quadcopter or even a GPS device.
The new quadcopter must have at least a 3-axis accelerometer (3 spatial coordinates xyz) and a gyroscope to detect the rotation. The alternative to these two sensors is an IMU device.
Now, I'll need do a work research. In the end, I will compare the prices to make the best choice. But I appreciate suggestions.

I already have the brushless motors.

I just get the box with the brushless motors (ROXXY 2827-34), propellers (EPP1045 - 10 x 4,5") and some screws, spacers, nuts, vibration dampeners, a LED strip and a transparent heat shrink tube. Now, is just missing the speed controllers for brushless motors.

Selecting a electronic speed control for the brushless motors.

In this version of the quadcopter, I will use the brushless motor Roxxy Outrunner 2827-34. The recommended speed controller by the manufacturer of the motor is the BL-Control 808 or 818. I choose the BL-Control 818. The only differences are in load current (8A/18A), peak (12A/22A) and weight (12g/13g).
Now I need find a way to connect the electronic speed control (ESC) to the arduino board using the PWM connections, and with the right code would I be able properly manipulate the ESC through the arduino. I hope. But, what is the PWM and PPM and where is it used? I found this site that explains in a simple manner, the means and the techniques associated with each word.
After some research I found a forum with some information on how to control the a brushless motor from the arduino board. Also check this post from the Farshid's Weblog and the page about the software Servo library from the Arduino Playground.

The new frame - version 3.0.

Figure 1

The new frame (third version) is almost complete. Several changes were made in comparison with the previous frame. The polyethylene foam tubes of the landing gear were replaced by strips of PVC plastic with a rubber band in the middle. New motor mounts have been added. The structure was enhanced (increased the weight). The 4mm carbon tubes and the connectors from the kites continue to be used to form the structure of the quadcopter.

Figure 2

In figure 2 we can see a detailed view from above. The central box is similar to the previous, but this box is riveted.

Figure 3

 In figure 3 we can see a detailed view from the side.

Figure 4

In figure 4 we can see a detail of the landing gear. This landing gear offers less resistance to air.

A box from Spain just arrived.

The screws, the plastic connectors and the motor mounts have just arrived. The new frame of the quadcopter based on the Arduino board is already taking shape.