47 lines
2.3 KiB
Markdown
47 lines
2.3 KiB
Markdown
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# DJI Gimbal Retro-Engineering
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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. This high quality gimbal is very tiny and easy to find as replacement part which makes it very suitable for DIY projects.
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## Description
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todo
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## Pinout identification
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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.
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Here is the strategy I followed to find the pinout:
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1. Find all equipotential pins:
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With a multimeter set to continuity tests, and test all the combinations
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2. Group remaining pins by motor
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With the multimeter find all the pins connected to the motor connector. (Reapeat 3 times)
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3.
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### Open-loop control
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Each motor has its own drivers a MP6536. Which makes it easy as no additional hardware is necessary to drive the motors.
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There are 4 pins from the MP6536:
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1. PWM1
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2. PWM2
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3. PWM3
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4. Fault : Output. When low, indicates overtemperature, over-current, or under-voltage.
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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.
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## Position estimation with the integrated linear hall sensors
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### 1. Setup
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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.
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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.
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### 2. Measures
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These oscilloscope traces are the sensor output when rotating the rotor forth and back. (a bit less than 180º on the 3rd motor)
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The channel 0 (Yellow) is the Hall 1 and the Channel 1 (Green) is the Hall 2
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### 3. Analysis
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We can see that in the first movement (positive rotation), the green is out of phase and opposite
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### 4. Encoder strategy
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