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Update readme: Add breakout board

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Lucien Renaud 2022-05-25 18:46:08 +02:00
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README.md
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@ -2,19 +2,21 @@
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
![](docs/overview.jpg)
<img src="docs/overview.jpg" height=250>
<img src="docs/working.gif" height=250>
## 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.
![Setup](docs/setup.jpg)
<img src="docs/setup.jpg" height=250>
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 for the other connectors)
<img src="Kicad/Breakout_DJI_Gimbal.png" height=500>
### 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.
@ -24,14 +26,14 @@ There are 4 pins from the MP6536:
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.
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
### 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](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.
@ -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)
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.`
![Sinwave figure](docs/cosSinEncoderDiagram.png)
<img src="docs/cosSinEncoderDiagram.png" height=250>
### 3. Encoding the position
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)
![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.
![Drilling](docs/drilling.jpg)
![Tunrning](docs/freeturn.gif)
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.
<img src="docs/drilling.jpg" height=250>
<img src="docs/freeturn.gif" height=250>
## Working
![Working](docs/working.gif)