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Update readme: Add breakout board

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README.md
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The aim of this project is to be able to use the 3-axis DJI gimbal with a custom open source controller like [SimpleFOC](https://docs.simplefoc.com/). This high quality gimbal is very tiny and easy to find as a replacement part which makes it very suitable for DIY projects. The aim of this project is to be able to use the 3-axis DJI gimbal with a custom open source controller like [SimpleFOC](https://docs.simplefoc.com/). This high quality gimbal is very tiny and easy to find as a replacement part which makes it very suitable for DIY projects.
## Description <img src="docs/overview.jpg" height=250>
<img src="docs/working.gif" height=250>
![](docs/overview.jpg)
## Pinout identification ## Pinout identification
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. 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.
![Setup](docs/setup.jpg)
<img src="docs/setup.jpg" height=250>
Here is the strategy I followed to find the pinout: Here is the strategy I followed to find the pinout:
1. Find all equipotential pins with a multimeter set to continuity tests, and test all the combinations 1. Find all equipotential pins with a multimeter set to continuity tests, and test all the combinations
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) 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)
<img src="Kicad/Breakout_DJI_Gimbal.png" height=500>
### Open-loop control ### Open-loop control
Each motor has its own drivers a MP6536. Which makes it easy as no additional hardware is necessary to drive the motors. Each motor has its own drivers a MP6536. Which makes it easy as no additional hardware is necessary to drive the motors.
@ -24,14 +26,14 @@ There are 4 pins from the MP6536:
3. PWM3 3. PWM3
4. Fault : Output. When low, indicates overtemperature, over-current, or under-voltage. 4. Fault : Output. When low, indicates overtemperature, over-current, or under-voltage.
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. Connected directly to a MCU (here a STM32 Nucleo F401RE) 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.
## Position estimation with the integrated linear hall sensors ## Position estimation with the integrated linear hall sensors
### 1. Setup ### 1. Setup
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. 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) <img src="docs/Hallmotor.jpg" height=300>
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. 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.
@ -39,11 +41,12 @@ Ratiometric means that the output signal is proportional to the voltage supply t
These oscilloscope traces are the sensor output when rotating the rotor forth and back. (a bit less than 180º on the 3rd motor) 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 The channel 0 (Yellow) is the Hall 1 and the Channel 1 (Green) is the Hall 2
![hall sensors traces](docs/courbes.png) <img src="docs/courbes.png" height=300>
We can see that in the first movement (positive rotation), the green is out of phase of π/2.` We can see that in the first movement (positive rotation), the green is out of phase of π/2.`
![Sinwave figure](docs/cosSinEncoderDiagram.png) <img src="docs/cosSinEncoderDiagram.png" height=250>
### 3. Encoding the position ### 3. Encoding the position
1. Get the absolute angle within a period 1. Get the absolute angle within a period
@ -100,10 +103,8 @@ float dist_angle(float newAngle, float prevAngle) // return the difference modul
To achive position control it is necessary to have first, a velocity controller well tuned, as they are in cascade. (SimpleFOC implementation and diagram) To achive position control it is necessary to have first, a velocity controller well tuned, as they are in cascade. (SimpleFOC implementation and diagram)
![Closed loop position diagram from SimpleFOC](docs/angle_loop_v.png) ![Closed loop position diagram from SimpleFOC](docs/angle_loop_v.png)
However, the motors of the gimbal have hard stop and can only rotate of around a half turn. It was so necessary to remove these mecanical stops. I drilled with a 1.6mm drill the two little holes to remove it. Then the motor was able to rotate freely. However, the motors of the gimbal have hard stop and can only rotate of around a half turn. It was so necessary to remove these mecanical stops. I drilled with a 1.6mm drill the two little holes to remove it. Then the motor was able to rotate freely and PID can be tuned.
![Drilling](docs/drilling.jpg) <img src="docs/drilling.jpg" height=250>
![Tunrning](docs/freeturn.gif) <img src="docs/freeturn.gif" height=250>
## Working
![Working](docs/working.gif)