# DJI Gimbal Retro-Engineering

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. 

## Description

todo

## 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. 
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
2. Group remaining pins by motor
With the multimeter find all the pins connected to the motor connector. (Reapeat 3 times)
3. 

### 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. 
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.

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.

## Position estimation with the integrated linear hall sensors

### 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. 

![Photo of the stator](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](LinearHallTrace_3rd_motor_120deg.png)

### 3. Analysis

We can see that in the first movement (positive rotation), the green is out of phase and opposite 
### 4. Encoder strategy