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Open-source firmware for Blue's motor controller
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Latest commit 7c28619 Oct 15, 2019

README.md

Getting Started

cd ~
git clone https://github.com/berkeleyopenarms/bldc-controller.git
cd bldc-controller
git submodule update --recursive --remote --init
sudo apt-get install gcc-arm-none-eabi

Compiling

cd ~/bldc_controller/<firmware or bootloader>
make

Debugging via ST-LINK

To debug during execution, you can attach the debugger at any time using the following code. Keep in mind this is done with a direct connection to the hardware via an ST-Link.

cd ~/bldc_controller/<firmware or bootloader>
openocd
----
cd ~/bldc_controller/<firmware or bootloader>/build
arm-none-eabi-gdb or gdb-multiarch <compiled file>.elf
(gdb) target extended-remote :3333

This functionality is also built into the make files as make debug.

Uploading via ST-LINK

cd ~/bldc_controller/<firmware or bootloader>
make upload

Upload firmware via RS485

cd ~/bldc_controller/tools
python upload_firmware.py <serial_port> <board_ids> ~/bldc_controller/firmware/build/motor_controller.bin

Upload bootloader via RS485

Use this with caution. If this fails and a power cycle or reboot occurs, the board will have to be programmed directly. In the case of a failed upload, disable the enumeration procedure and try again with the same board ID. To be safe, first upload and test on an easy-to-remove link such as the gripper or base which are not as difficult to access in case of a failure.

upload_bootloader.py <serial_port> <board_id> <path_to_file>

Serial Transmission Speed Limits

USB Serial device drivers only permit at most one transmission per millisecond. By default, this is set to 16 milliseconds on our usb to RS485 converters. To change this execute the following terminal commands:

cat /sys/bus/usb-serial/devices/ttyUSB<id_num>/latency_timer
setserial /dev/ttyUSB<id_num> low_latency
cat /sys/bus/usb-serial/devices/ttyUSB<id_num>/latency_timer

(when running the arm, this is done automatically by the ROS control stack)

Python Scripts

These scripts are made to remotely interface with the boards. They can debug, program, and run the boards. They interface using our custom communications protocol. Most scripts have been fitted with argparse which will give a description of the arguments when given the '-h' option. (i.e. read_sensor.py -h)

Motor Calibration

To calibrate the motor board, a motor must first be attached without a load for optimal calibration. The results of calibration are based on the properties of the given motor.

  • calibrate_encoder.py <serial_port> <board_id> <duty_cycle>
  • upload_calibration.py <serial_port> <board_id>
  1. Run calibrate_encoder.py: for 24V Power Supplies the duty cycle used in testing is 0.3 and for 48V or 50V supplies use half (0.15). This will generate a file called calibrations.json
  2. Run upload_calibration.py with the updated calibrations.json and the generated file will be loaded onto the board.

After completing these steps, the motor should be controllable.

Update Motor Calibration Constants (PID and Limits)

Run this script after there's a calibration on the board. Modify the contents of the script to adjust tunings!

update_calibration.py <serial_port> <board_id>

Motor Control

Use this script to spin a motor with a given current command. A substantial starting point is 0.5 and increase above this with proper supervision! A negative command will reverse the direction. Description of what arguments each mode takes can be found with the '-h' option.

control_motor.py <serial_port> <board_id> <mode> <command>

To control multiple motors,

control_motor.py <serial_port> 1,2,3 torque 0.5,0.25,0
control_motor.py <serial_port> 1,2,3 current [0,0.5],[0,0.25],[0,0]

Read Sensor

This script lets a user read from any of the sensors on-board the device.

read_sensor.py <serial_port> <board_ids> <sensor>

View Control Loop

Plots the control target and the resulting quadrature/direct current commands. This is low frequency so use the recorder to get a better sense of the internal state of the motor driver.

Recording

These scripts start and read off an on-board buffer of the commutation at each control cycle. There are included plotting scripts. This interfaces directly with the Recorder class in the firmware.

System Design

The BLDC is built on ChibiOS. The operating system allows for quick development and thread management which have been useful for this fast-paced project. To supplement missing features, the STM32 library has been included. Memory is allocated primarily for firmware though two blocks are used to store the calibration and board id (refer to section 3.3 of reference manual for memory).

Common

In both firmware and bootloader, the primary system is the communication code. This is designed to allow users to read/write variables as well as reprogram the board remotely. When a board receives a packet, a small green LED will blink to indicate it has identified the message.

Bootloader [Flash Sector 0]

This small system is primarily meant as a method to allow updates of the firmware without a programmer. On command, it will move the program counter to the start of the firmware code.

LED Indicator

During normal operation, the bootloader will pulse the RGB LED blue.

Board ID [Flash Sector 1]

To keep track of the board ID when switching between firmware and bootloader, and in case of a system fault, the board id is stored in flash.

Calibrations [Flash Sector 2]

To keep calibrations between restarts, a section of flash is reserved and loaded to/from by firmware. Once a calibration is stored, it will load on boot without host intervention. To modify the calibration, either re-calibrate the motor or use the update_calibration.py tool.

Firmware [Flash Sectors 4 - 11]

The firmware code starts by initializing hardware devices and then splits into a number of threads.

LED Indicator [low priority]

During normal operation, the firmware will pulse the RGB LED green. If a red or blue pulse is seen while in firmware, the driver chip Fault and/or OTW pins have activated. Refer to the DRV8312 datasheet for the type of fault.

Sensor Thread [low priority]

Pulls updates from the accelerometer and temperature sensor.

Communication Thread [normal priority]

Used to update motor targets and read current position, velocity, accelerometer data, temperature, etc.

Control Thread [high priority]

Pulls updates from ADC for current/voltage measurements as well as queues reads to the absolute encoder. With this data, FOC is computed with output duty cycles to STM32 timing hardware.

Independent Watchdog Thread [high priority]

Used to keep the system live while protecting from the chance of a hard fault or any other unforseen errors. When a lock-up occurs, the system will reset into bootloader which will then check the watchdog reset flag. If it is active, the bootloader will return the system to firmware mode.

Modifying Pins

All of the code can be directly modified except for the pins (althought you can technically modify it directly too). To allow for the pin definitions and defaults to be auto-generated and easily maintained, please make any modifications in ChibiStudio and generate new pin files from the studio interface.

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