02/14/2019 at 15:04 •
After moving to another city, the development of the system PCBs had to be halted for some time. Due to a lack of space, I had to focus most of the work on this project on the computer. My new job created an opportunity to revive a n-body simulation program I have written during the physics course, around the 90s. This program allowed me to simulate configurations of particles and springs interacting through well known laws and visualize them through virtual 3D cameras. I upgraded it to run on multiprocessor machines and moved all the code to C++, using SDL as a plotting tool and CERN ROOT to plot graphs.
Testing the real tricopter became a dangerous task. The control system PIDs need to read sensor data and control engine power. I had to tie the tricopter to a string connecting the room ceiling to a 20kg water bottle that was hanging on it. When the control system was turned on, the engines could go to maximum speed and destroy something around, even with the tricopter tied. Testing the control system in a real system proved to be tricky.
I decided to unite both efforts and build a simple tricopter model on the simulation program. I used a four particle model with particles connected by hi-K springs. Three particles behaved as the three engines, the fourth behaving as a payload. Their relative positions can be controlled by parameters.
The forces that are applied on the three engine particles are the near same forces that would apply to the engines. And they would be defined by the PIDs that control the real tricopter. A servo was simulated to deflect the tail engine air flow and counteract residual torque. By monitoring the tricopter gravity center and particle configuration I could calculate the sensor data thus simulating a magnetometer, an accelerometer and a gyroscope. A virtual planet was also simulated to give me geographical coordinates for the simulated GPS and a magnetic field for the magnetometer.
Tuning the PID parameters on the simulated system proved to be as difficult as doing it in a real system. The good part is that I would not hurt my fingers on real propellers. After many, many tries and different PID connection configurations, I reached a more or less stable system and decided to code some genetic algorithm programing on the simulation. Now I had populations of tricopters that tried to stay near a waypoint as long as possible. The best of them was used as a seed for the next generation. PID gains were perturbed along the population to generate more or less adaptable individuals.
It turned out that a perturbing many parameters at a time, even slightly, did not produce optimal results. The selection process was taking many generations to produce a better individual, and its performance was far from the one I expected, so I decided to restart tuning the PIDs of a single individual manually. I also changed the PIDs arrangement, to use the maximum amount of sensor information I could.
Today I believe to have reached a milestone. The video below shows the latest result. The red cross is the tricopter waypoint, which is moving because the small planet below it is rotating slowly. The forces produced by the engines are plotted in white, while the control system desired heading is shown in red or blue, depending on the distance to the waypoint.
Now I believe this control code can be used on the real tricopter system.
09/10/2017 at 17:00 •
Today I'm posting a picture of the CoolTerm terminal connected to the communications module via a serial connection.
What can be seen are many telemetry sequences starting with ### and using # as a separator between the four bytes that represent each relevant system variable value. I made a small C++ program to parse the telemetry and show the data on the screen.
A tall matrix can be seen on the serial terminal too. Each line of the matrix represents a capacity that an installed module can have. Modules can have accelerometers or other sensors installed, for example. Or they can be able to pilot the vehicle, or they can control servos. All the current capacities are listed in the following link: https://pastebin.com/KBw1i5Ui
The matrix shows that the module installed on slot 4 have an accelerometer, a gyroscope, a barometer and a magnetometer.
By using a matrix like this the data from similar sensors can be fused together using this equation:
And this operation can be done in a simple loop, taking care of the possibility of sensor redundancy in a very simple way.
Your comments are important and welcome.
You can find me online on the #avr and #sparkfun channels of the Freenode IRC servers. People from those channels are very nice and have contributed with solutions to programming problems and hardware related ones.
07/23/2017 at 19:44 •
Hi. I tried to laser cut a prototype of the possible new PCBs on paper. The results are shown below:
As I'm using a very low power (500mW) 808nm laser diode, the cutting speed must be very small (25mm/min), so patience is a must.
Parts were drawn on Sketchup, exported as STL and converted to G-Code using MeshCAM. They were fed to the CNC controller (tiny-g) using a software I made and called YetAnotherGCodeSender. Source code is publicly available. The CNC is a modified ShapeOko2.
Here is the pre-assembling:
And this is the final result:
As always, your comments are welcome!
07/20/2017 at 02:04 •
Hello. After many suggestions and critics, this is the second candidate for the next generation PCB set. Please let me know what you think. This version is mechanically interlocked to increase strength and reduce the stress on the joining solders.
07/19/2017 at 16:02 •
I'd like to ask your opinion about the following drawings. I'm thinking of designing the new generation of project PCBs in the way displayed below.
Making them like that would enable me to use the PCBs as PCBs and as a structural support for the modules, with the benefit of eliminating the annoying module connectors and module vibration.
All the displayed parts are PCBs. They would be mechanically attached to each other using the slots and fixed in position using solder pads. Modules would be electrically connected to the box using solder points on the bottom and on the sides, which could also carry more connections such as a redundant power rail, or a redundant SPI bus. Modules would also gain more space, being able to grow a bit to the sides if needed.
I need your expertise. You have a unique view about this possibility and can help a lot this project by sharing it here. Please let me know what you think.
06/25/2017 at 04:05 •
After a lot of testing and debugging of the servo module, I discovered I made a horrible mistake in the module project. I forgot the I2C pull-up resistors. Fixing it was not easy, but was done. I soldered two 10k resistors over the SDA and SCL lines of the servo module and connected them to the 3v3 line. Another big problem I faced was the PCA9685 I2C addressing which was calculated in the wrong way by me. The logic level analyzer I bought at DX.com for 9USD helped a lot to find and fix the error.
It the spare time of two weeks to find and fix all the errors, but now the module has 16 working PWMs ready to control the servos.The prototype can be seen working in the video below.
Next step is to plug the module in the YAUVC backbone and start controlling it via WIFI, or let the flight control module take care of it.
06/06/2017 at 01:10 •
Today I managed to put everything done until now together, building what is now called the YAT: Yet Another Tricopter!
The thing has three electric motors, three ESCs, one servo, a switching 3.3V power supply (the 3.3v module is flawed), and the YAUVC backbone with some modules. This platform will work as a testbed for the servo control module and for the control algorithms that will try to make the YAT fly. Instead of the battery, I connected the YAT to a power supply via a cable. Communication to the YAUVC is done via WiFi. Here are some pictures:
Next step is to develop the code for the servo control module.
Soon I hope to come back with more good news.
And, if you want to follow this project more closely, you can join the @labvant.com Telegram group, where I'll be posting more frequent updates and pictures.
Thanks again for all your help and support!
06/01/2017 at 01:22 •
After five months traveling at the back of a drunk snail, the components I ordered from China have finally arrived. Today I managed to assemble the servo control submodule and here is the first picture of it:
This submodule is controlled by the MCU module via a two wire interface (TWI). The MCU module talks to the rest of the system via a SPI interface available from the main bus. The submodule have 16 pins to connect to the servos. They are the ones in a 4x4 matrix. The four pins below them are connected to 5V and ground.
Having 16 servo plugs directly available on this PCB would make it too big to fit into the system. I decided to interface servo plugs with this board elsewhere. This will require some wires to be soldered to this board with male servo connections on the other end. The number of wires will depend on the required number of servos for each project.
Below is a picture of the submodule connected to a MCU module.
The headers still need to be trimmed, I know. They will be soon. I'm now going to work on this module's code. As soon as it is working, I'll make it available in the project repository.
Thank you for your help and support. I'd also like to thank Hackaday.io for the help they have given to this project, and to many others, through their great work. I have received a message from them last week saying that the project was one of many awarded with seed money. This was great news for me!
Soon this whole thing will be piloting a tricopter, or a glider, or just a small wheeled robot. Or a flying toilet. Who knows?
04/27/2017 at 18:41 •
Hi! I'm happy to inform that, due to a nice partnership between Hackaday and FindChips, I can now share the BOMs (bill of materials) of two of the project modules. More lists are coming in the next logs, but the first two ones are here:
MCU module BOM: https://www.findchips.com/u/list/28455-mcu-module
PS module BOM: https://www.findchips.com/u/list/28469-ps-module
Thanks, Hackaday and FindChips for this amazing new feature!
03/10/2017 at 06:08 •
Hi. I'm working on the flight control module code. I added a few new classes: Navigation, PID, FCM (Flight Control Module), SCM (servo control module), GPS (GPS module) and a very abstract GNC (guidance, navigation and control) class. My main objective is to make GNC the main class for vehicle stabilization. All other vehicle specific attitude control classes should derive from it. Some of the new classes have only the very basic structures needed to integrate them with the system, but FCM inherited code I have already tested against FlightGear in the past, and is able to take a simulated airplane from waypoint a to waypoint b without crashing it.
I regenerated the documentation and uploaded it to labvant.com website. The absence of comments is proportional to the absence of my free time, but doxygen does a great work crossing, formatting and displaying code. Generating documentation with Doxygen was a suggestion from an IRC collaborator: NoHitWonder.
About the new submodules, a brushless motor control module has already been drafted with the help of Erlend^SE, another project IRC channel collaborator. He is also inspiring and helping with the development of a new power supply module and a ESP8266 module to substitute the RN131G. You can join the project IRC channel by connecting your IRC client to a free node IRC server and joining #labvant.com.
If you like how this project is evolving, please consider supporting it by helping to develop the electronics, the code or the firmware. All the project info is publicly available on the project repo, including schematics, PCB drawings and firmware code in C++. You can also develop your own modules using the project board/connection standards, or propose new standards for future systems. Supporting this project financially by sending a $1 PayPal donation is also welcome. That will help covering the PCB and equipment costs. Thanks a lot for your help and support!