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README.md
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# DJI Gimbal FOC # DJI Gimbal FOC
Control for the DJI gimbal The aim of this project is to be able to use the 3-axis DJI gimbal with a custom open source controller. This high quality gimbal is very tiny and easy to find as replacement part which makes it very suitable for DIY projects.
## Getting started
To make it easy for you to get started with GitLab, here's a list of recommended next steps.
Already a pro? Just edit this README.md and make it your own. Want to make it easy? [Use the template at the bottom](#editing-this-readme)!
## Add your files
- [ ] [Create](https://docs.gitlab.com/ee/user/project/repository/web_editor.html#create-a-file) or [upload](https://docs.gitlab.com/ee/user/project/repository/web_editor.html#upload-a-file) files
- [ ] [Add files using the command line](https://docs.gitlab.com/ee/gitlab-basics/add-file.html#add-a-file-using-the-command-line) or push an existing Git repository with the following command:
```
cd existing_repo
git remote add origin https://gitlab.inria.fr/imia/dji-gimbal-foc.git
git branch -M main
git push -uf origin main
```
## Integrate with your tools
- [ ] [Set up project integrations](https://gitlab.inria.fr/imia/dji-gimbal-foc/-/settings/integrations)
## Collaborate with your team
- [ ] [Invite team members and collaborators](https://docs.gitlab.com/ee/user/project/members/)
- [ ] [Create a new merge request](https://docs.gitlab.com/ee/user/project/merge_requests/creating_merge_requests.html)
- [ ] [Automatically close issues from merge requests](https://docs.gitlab.com/ee/user/project/issues/managing_issues.html#closing-issues-automatically)
- [ ] [Enable merge request approvals](https://docs.gitlab.com/ee/user/project/merge_requests/approvals/)
- [ ] [Automatically merge when pipeline succeeds](https://docs.gitlab.com/ee/user/project/merge_requests/merge_when_pipeline_succeeds.html)
## Test and Deploy
Use the built-in continuous integration in GitLab.
- [ ] [Get started with GitLab CI/CD](https://docs.gitlab.com/ee/ci/quick_start/index.html)
- [ ] [Analyze your code for known vulnerabilities with Static Application Security Testing(SAST)](https://docs.gitlab.com/ee/user/application_security/sast/)
- [ ] [Deploy to Kubernetes, Amazon EC2, or Amazon ECS using Auto Deploy](https://docs.gitlab.com/ee/topics/autodevops/requirements.html)
- [ ] [Use pull-based deployments for improved Kubernetes management](https://docs.gitlab.com/ee/user/clusters/agent/)
- [ ] [Set up protected environments](https://docs.gitlab.com/ee/ci/environments/protected_environments.html)
***
# Editing this README
When you're ready to make this README your own, just edit this file and use the handy template below (or feel free to structure it however you want - this is just a starting point!). Thank you to [makeareadme.com](https://www.makeareadme.com/) for this template.
## Suggestions for a good README
Every project is different, so consider which of these sections apply to yours. The sections used in the template are suggestions for most open source projects. Also keep in mind that while a README can be too long and detailed, too long is better than too short. If you think your README is too long, consider utilizing another form of documentation rather than cutting out information.
## Name
Choose a self-explaining name for your project.
## Description ## Description
Let people know what your project can do specifically. Provide context and add a link to any reference visitors might be unfamiliar with. A list of Features or a Background subsection can also be added here. If there are alternatives to your project, this is a good place to list differentiating factors.
## Badges todo
On some READMEs, you may see small images that convey metadata, such as whether or not all the tests are passing for the project. You can use Shields to add some to your README. Many services also have instructions for adding a badge.
## Visuals ## Pinout identification
Depending on what you are making, it can be a good idea to include screenshots or even a video (you'll frequently see GIFs rather than actual videos). Tools like ttygif can help, but check out Asciinema for a more sophisticated method. The Gimbal is composed of a flex PCB with a main connector and 3 smaller for each motor. The main end connector is a 40-pin mezzanine board to board connectors. In order to work easily I have designed a breakout board which open to a 2.54" header.
## Installation
Within a particular ecosystem, there may be a common way of installing things, such as using Yarn, NuGet, or Homebrew. However, consider the possibility that whoever is reading your README is a novice and would like more guidance. Listing specific steps helps remove ambiguity and gets people to using your project as quickly as possible. If it only runs in a specific context like a particular programming language version or operating system or has dependencies that have to be installed manually, also add a Requirements subsection.
## Usage
Use examples liberally, and show the expected output if you can. It's helpful to have inline the smallest example of usage that you can demonstrate, while providing links to more sophisticated examples if they are too long to reasonably include in the README.
## Support Here is the strategy I followed to find the pinout:
Tell people where they can go to for help. It can be any combination of an issue tracker, a chat room, an email address, etc. 1. Find all equipotential pins with a multimeter set to continuity tests, and test all the combinations
## Roadmap 2. Group remaining pins by motor With the multimeter find all the pins connected to the motor connector. (Reapeat 3 times for the other connectors)
If you have ideas for releases in the future, it is a good idea to list them in the README.
## Contributing ### Open-loop control
State if you are open to contributions and what your requirements are for accepting them.
For people who want to make changes to your project, it's helpful to have some documentation on how to get started. Perhaps there is a script that they should run or some environment variables that they need to set. Make these steps explicit. These instructions could also be useful to your future self. Each motor has its own drivers a MP6536. Which makes it easy as no additional hardware is necessary to drive the motors.
There are 4 pins from the MP6536:
1. PWM1
2. PWM2
3. PWM3
4. Fault : Output. When low, indicates overtemperature, over-current, or under-voltage.
You can also document commands to lint the code or run tests. These steps help to ensure high code quality and reduce the likelihood that the changes inadvertently break something. Having instructions for running tests is especially helpful if it requires external setup, such as starting a Selenium server for testing in a browser. Connected directly to a MCU and with the Simple FOC Library, open-loop control works quite well. However due to open-loop control, it cannot know when a "step" is missed so misalignment can occur. Also, the motor tends to become quite hot due to the continuous current sent to the coils.
## Authors and acknowledgment ## Position estimation with the integrated linear hall sensors
Show your appreciation to those who have contributed to the project.
## License ### 1. Setup
For open source projects, say how it is licensed. Each motor is composed of two ratiometric linear hall sensors. (Texas Instrument DRV5053 Analog-Bipolar Hall Effect Sensor) They are placed at around 120º from each other (eyes measured) and measure the magnetic field of the rotor.
![Photo of the stator](docs/Hallmotor.jpg)
Ratiometric means that the output signal is proportional to the voltage supply to the sensor. In this setup, with 5V supply, the output measured is between 520mV and 1.5V, so a 1V amplitude.
### 2. Measures
These oscilloscope traces are the sensor output when rotating the rotor forth and back. (a bit less than 180º on the 3rd motor)
The channel 0 (Yellow) is the Hall 1 and the Channel 1 (Green) is the Hall 2
![hall sensors traces](docs/courbes.png)
We can see that in the first movement (positive rotation), the green is out of phase of π/2.`
![Sinwave figure](docs/cosSinEncoderDiagram.png)
### 3. Encoding the position
1. Get the absolute angle within a period
Since the 2 signals correspond to a cos and sin signals, it is possible to compute the angle inside the period using arctan2 function. However, we have more than one period, it is so necessary to increment a position.
$$\theta= atan2(a,b)$$
2. Incremental position
To increment the position, it is necessary to start from 0 at a known postion. For that the motor is moved in open loop to one end and the position is set to 0.
Then we need to sum all the delta of movement at each measure sample.
$$\phi_t=\phi_{t-1} + (\theta_t - \theta_{t-1})mod(-\pi;\pi)$$
## Coding the solution
1. Get the angle in the perdiod
In order to compute the angle from the cos and sin with atan, it is necessary to remap the values of the analog readings from -1 to 1.
Beforehand, the maximum and minimum peak of the signals need to be found. It can be done by swiping the motor on startup in open-loop mode.
Then the arctan function can be applied. It is preferable to use arctan2 as it will give an angle within the 4 quadrants (-π,π). Whereas arctan give an angle between (-π/2,π/2). [Wikipedia](https://en.wikipedia.org/wiki/Atan2)
```C++
float LinearHallSensor::Callback() // Return the estimated position of the sensor
{
A = norm(analogRead(CH1),minCh1, maxCh1); //read analog values and normalise between [-1;1]
B = norm(analogRead(CH2),minCh2, maxCh2);
theta = atan2(A,B); // Compute the absolute angle in the period
phi = phi + dist_angle(theta, theta_prev); // increment the difference
theta_prev = theta; // save fot nex time
return phi;
}
float norm(float x, float in_min, float in_max) //return the input value normalised between [-1;1]
{
return (float)(x + 1.0) * (2.0) / (float)(in_max - in_min) -1.0;
}
float dist_angle(float newAngle, float prevAngle) // return the difference modulo [-pi;pi]
{
float diff = newAngle - prevAngle;
while (diff < (-M_PI))
diff += 2 * M_PI;
while (diff > M_PI)
diff -= 2 * M_PI;
return diff;
}
```
## Project status
If you have run out of energy or time for your project, put a note at the top of the README saying that development has slowed down or stopped completely. Someone may choose to fork your project or volunteer to step in as a maintainer or owner, allowing your project to keep going. You can also make an explicit request for maintainers.

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docs/LinearHallEncoder.md
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@ -45,13 +45,16 @@ We can see that in the first movement (positive rotation), the green is out of p
![Sinwave figure](cosSinEncoderDiagram.png) ![Sinwave figure](cosSinEncoderDiagram.png)
### 3. Encoding the position ### 3. Encoding the position
1. Get the angle of one periodic signal 1. Get the absolute angle within a period
Since the 2 signals correspond to a cos and sin signals, it is possible to compute the angle inside the period using arctan2 function. Since the 2 signals correspond to a cos and sin signals, it is possible to compute the angle inside the period using arctan2 function. However, we have more than one period, it is so necessary to increment a position.
$$\theta= atan2(a,b)$$
2. Incremental position 2. Incremental position
- increment periods
- start from known position (one end) To increment the position, it is necessary to start from 0 at a known postion. For that the motor is moved in open loop to one end and the position is set to 0.
Then we need to sum all the delta of movement at each measure sample.
$$\phi_t=\phi_{t-1} + (\theta_t - \theta_{t-1})mod(-\pi;\pi)$$
## Coding the solution ## Coding the solution
1. Get the angle in the perdiod 1. Get the angle in the perdiod
@ -61,14 +64,35 @@ Beforehand, the maximum and minimum peak of the signals need to be found. It can
Then the arctan function can be applied. It is preferable to use arctan2 as it will give an angle within the 4 quadrants (-π,π). Whereas arctan give an angle between (-π/2,π/2). [Wikipedia](https://en.wikipedia.org/wiki/Atan2) Then the arctan function can be applied. It is preferable to use arctan2 as it will give an angle within the 4 quadrants (-π,π). Whereas arctan give an angle between (-π/2,π/2). [Wikipedia](https://en.wikipedia.org/wiki/Atan2)
```C++ ```C++
float norm(float x, float in_min, float in_max)
float LinearHallSensor::Callback() // Return the estimated position of the sensor
{
A = norm(analogRead(CH1),minCh1, maxCh1); //read analog values and normalise between [-1;1]
B = norm(analogRead(CH2),minCh2, maxCh2);
theta = atan2(A,B); // Compute the absolute angle in the period
phi = phi + dist_angle(theta, theta_prev); // increment the difference
theta_prev = theta; // save fot nex time
return phi;
}
float norm(float x, float in_min, float in_max) //return the input value normalised between [-1;1]
{ {
return (float)(x + 1.0) * (2.0) / (float)(in_max - in_min) -1.0; return (float)(x + 1.0) * (2.0) / (float)(in_max - in_min) -1.0;
} }
A = norm(analogRead(CH1),minCh1, maxCh1); float dist_angle(float newAngle, float prevAngle) // return the difference modulo [-pi;pi]
B = norm(analogRead(CH2),minCh2, maxCh2); {
float diff = newAngle - prevAngle;
while (diff < (-M_PI))
diff += 2 * M_PI;
while (diff > M_PI)
diff -= 2 * M_PI;
return diff;
}
angle = atan2(A,B);
``` ```