ST Design Competition: McGill Team Wins 1st Place
The ST iNEMO Platform Design Contest was conducted by ST Microelectronics and Digikey, and was open to all engineering students from the Americas. The purpose of the competition was to devise an innovative and appealing application to showcase the capabilities of the ST iNEMO kit. It was also important to integrate this kit with extension boards, dedicated firmware, and a graphical user interface.
The iNEMO kit is basically a little computer consisting of an inertial measurement unit (IMU) and various other sensors. The IMU is comprised of three accelerometers, three gyroscopes, and three magnetometers,which continuously measure linear, angular,and magnetic motion about the “X”, “Y”,and “Z” axes. The other sensors are the onboard temperature and pressure sensors which measure environmental data.
The Idea
For the final year design project, the team decided to participate in the design contest,under the supervision of Professor Zeljko Zilic. First, a suitable design that fulfills all the requirements of the competition had to be found. That meant looking for an application for all the various sensors that makeup the iNEMO.
Research showed that the most common applications of IMUs are for moving vehicles.Cars were deemed to be too simple to build and program since they basically only move in two dimensions. Boats were also considered but rejected for the same reason. A greater challenge was sought. Hence, the quadcopter!
A quadcopter is like a helicopter, but with four rotors in the same plane and no tail rotor. It must be able to balance itself in the horizontal plane and control its spin, direction of motion, and height. Additionally, the quadcopter had to be able to receive commands(via a remote) and stream sensor data wirelessly to a terminal.
The balance requirements were satisfied through the fusion of the accelerometers’, magnetometers’, and gyroscopes’ data, input to a control system which in turn regulates the four motors. Altitude control was satisfied through an independent GPS module which outputs altitude readings, as well as through the use of the barometric formula, which determines height from pressure and temperature. In this manner, all the sensors were used for practical purposes.
The Implementation
In order to build the quadcopter, we needed to build a frame capable of holding all the components, while being light enough to fly. Regular aluminum beams were used,with a central platform for all the electronics and small platforms for the motors. Eventually, the design was modified, but this was the basic idea. The central platform had to be insulated against mechanical vibration,as well as fluctuating environmental conditions and mechanical stresses, in case of crashes. A regular piece of plastic Tupperware was hence chosen. The iNEMO board,an ST wireless module, and a third ST processor were used for all computation on the quadcopter side. A PCB was made (by Ben)in order to connect all the devices.
On the remote control side, an ST processor,a wireless module, and an analog game controller were combined in order to acquire controller data and send these data wirelessly to the quadcopter.
Finally, on the PC side, a command line application was written, which received wireless data through a third wireless module,in order to display the various sensor data from the iNEMO.
Many revisions were made to the physical layout, including adding cowlings for the propellers, adding more insulation, as well as changes in the components. The wireless module was actually changed midway through the project, in order to incorporate more ST parts.
In terms of software, much debugging was done on all ends, separately by component, as well as together in one point of control(quadcopter, remote, pc), as well as for the total system. All components’ communications had to be verified, with multiple checks in order to shut down the system safely in case of erroneous signals.
Sensor fusion was accomplished both using the ST provided libraries for roll, pitch, and yaw, in addition to our own Kalman filter implementation, in order to compensate for small errors in the library. The settings for the control loop were determined through manual testing in order to make sure the copter compensates for tilt correctly such that no unstable reaction occurs.
Finally, all the hardware and software components of the project were combined for the first flight.
The Challenges
The team learned many practical engineering skills outside their field of experience:mechanical construction, embedded programming,component integration, sensor fusion, data analysis, and control systems.
All members were from either Electrical or Computer Engineering, and as a result, most of the team had minimal experience working on the mechanical aspects of a project.
There was also a great deal of embedded programming, with which some members were not familiar. Extensivere search into what makes a good IMU had to be done;that meant combining and filtering data from the various sensors in order to obtain meaningful representations.
Effective control systems also had to be designed in order to maintain stability.There were also many moments of frustration when aspects of the design that were tested independently functioned within parameters, but failed when integrated into the system as a whole. It was while dealing with these issues that many of the difficulties in creating multi-component systems and the importance of external (visual) debugging capabilities became most apparent. In the end, a controllable quadcopter based on the original design was built and operated.There are still some kinks to be worked out, but overall, the project was a success.All schematics and code were sent to STand Digikey.
We received notice on June 16th that our entry to the contest received the prize for first place. Second place was Stanford, who also made a quadcopter for their entry.First prize was $5000 and an all-expenses paid trip for two to Europe, including a visit to the STMicroelectronics factory. Additional prizes included $2500 and $1000cash prizes
