Aggressive Maneuvers for Autonomous Quadrotor Flight.

The video above shows a spectacular quadcopter. An authentic acrobat of the air. Demonstrations of pirouettes, flips, flight through windows, and quadrotor perching are shown. This spectacular device was developed at at the GRASP Lab, University of Pennsylvania. More information can be found at this site.

The first part of the quadcopter in 3D.

After some research I found several people who have 3D printers. I also discovered that there are sites that print the parts if we uploading the file with the 3D model and then send them by regular mail after printed. In many sites, you can also choose the material we want that our parts be printed.

Figure 1

I tried three 3D modeling tools available for Linux, Blender, Wings 3D and OpenSCAD. I found that the Blender is a complex tool but at the same time powerful, but requires a lot of learning for a beginner. Wings 3D is very easy to use but it is very difficult when you have to make the so called Boolean operations, ie, unions, subtractions and intersections. Finally, the OpenSCAD, is not a tool so much known, but it is a tool that does just the job I wanted to do, that is to make a 3D model for printing. The OpenSCAD uses a very simple scripting language for creating 3D models of parts. An example can be seen in Figure 1.

Figure 2

In Figure 2 we can observe the same part shown in Figure 1 with some minor differences, but made using the Wings 3D. An interesting use of the various tools is to use OpenSCAD to create the initial 3D model and then refines it with more detail using the Wings 3D or the Blender.
Another problem we have keep in mind when modeling the parts to print is to make a support for the parts if, the parts does not have a base for maintaining the equilibrium, to ensure that the parts does not move while being printed.

Finally, I got the 9 DOF Razor IMU board.

Yes, the 9 DOF Razor IMU board finally arrived. It is really very small. The three sensors, aceleromentro, gyroscope and compass in a single small board. The data provided by this board will be responsible for 3D orientation and stabilization of the quadcopter in the air. I already have some ideas of how to connect this board to the Arduino board. The following post published in the Arduino forum indicates a path to follow to read the data from the Arduino board. But after a quick search, I found there is not much information on how to use this board.

3D printer for rapid prototyping.

While I wait for the new electronic parts to arrive, I found a printer that prints 3D plastic objects. The most amazing thing is that extremely cheap compared to the price of industrial printers for rapid prototyping. This type of printer is more like a desktop printer. Some 3D printers, are open source community projects like the RepRap project. The following video shows how the RepRap 3D printer works.

The parts for the quadcopter were made by hand and they look rough. But with a 3D printer I can quickly make the parts and reduce the weight by replacing metal parts with plastic. I can also do more aerodynamic parts. To make the parts, it is necessary first to model the parts in a 3D software like Blender, Wings 3D or OpenSCAD and then save in a format that can be read by the 3D printer, usually in a stereolithography file (stl). Now I have to find someone who has a 3D printer near where I live that can print the parts, but first I have to model each part of the quadcopter in 3D. But it would be interesting to make a kit that people could then print and assemble using a 3D printer.

The best combination of sensors to make a flight controller.

To stabilize and guide the quadcopter autonomously - independent of the algorithms they are used - it needs the combination of multiple sensors. Initially, it will use an accelerometer, a gyroscope and a compass. To guide him inside of the buildings will use ultrasonic sensors. A simple GPS, will guide the helicopero between two points in outdoor environment.

After doing some research, I came to the conclusion that the best combination would be to use the board "IMU 6DOF Razor - Ultra-Thin IMU" with the board "Triple Axis Magnetometer Breakout - HMC5843". The first board makes use of ST's LPR530AL (pitch and roll) and LY530ALH (yaw) gyros, as well as the ADXL335 triple-axis accelerometer, to give six degrees of measurement. The second board is a breakout board for Honeywell's HMC5843, a 3-axis digital compass. Communication with the HMC5843 is simple and all done through an I2C interface. The two boards together provide nine degrees of measurement.

But when I had already decided by the combination indicated above, I discovered the same combination, but which joins the three sensors (aceleromentro, gyroscope and compass) in a single board. The board “9 Degrees of Freedom - Razor IMU - AHRS compatible” incorporates the same four sensors of the boards described above - an LY530AL (single-axis gyro), LPR530AL (dual-axis gyro), ADXL345 (triple-axis accelerometer), and HMC5843 (triple-axis magnetometer) - to give nine degrees of inertial measurement. The outputs of all sensors is processed by on-board ATmega328 and sent out via a serial stream. I think this is will be the best solution for an autonomous quadcopter.

What I've done until now.

The diagram above shows what I have been doing since I have started the motor controller. Indeed, it is still only a little bit. The most important part of the work will start now with the design and implementation of the flight controller. The first challenge is to deeply understand the dynamics of a “quadcopter” flight and then select the most appropriate control algorithms.

Basically, the quadcopter is an aerial vehicle and consists of a rigid frame with four motors mounted in the arms of the cross. Two pairs of perpendicular propellers rotate in opposite directions, one pair in a clockwise direction and another in the counter clockwise. When one varies the speed of a motor can change the lift and create motion, as well as increasing or decreasing the speed of the four propellers together generate a vertical motion. Changing the speed of the pair of propellers that run in a counter clockwise direction reciprocally produces roll rotation, along with lateral motion. Likewise, changing the speed of the pair of propellers, that run in a clockwise direction reciprocally produces the pitch rotation and the longitudinal motion. The difference in the counter-torque between each pair of propellers have as a result the yaw rotation.