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+# 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 
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