Brushed DC Motors

Our brushed motors are controlled with a custom PCB that we call the "3BM". This motor controller can control up to three brushed motors. It can support up to two limit switches per motor and a total of one absolute encoder and one quadrature encoder. We communicate with the board using CAN. The board communicates with the absolute encoder using I2C.

Code Structure

The driver code is in controller.cpp and the main motor control logic is in motor.hpp. Motor CAN IDs and the number of motors is configured in common.hpp. controller.cpp constructs up to three motors, initalizes the CAN bus, and starts the global timers.

Architecture

Below is a diagram of the 3BM architecture.

3bm firmware architecture diagram

Timer Overview

The 3BM uses seven hardware timers:

  • htim1 (PWM_TIMER_[0,1,2]): PWM timer for the three motors (TIM_CHANNEL_[0,1,2] for motor [0,1,2], respectively)
  • htim2 (GENERIC_ELAPSED_TIMER): Repeating count up timer where each tick is 0.001 ms (1000 ns). It used used by:
    • The absolute and quadrature encoder to measure how much time has elapsed since the last reading in order to measure velocity
    • The PIDF controller in order to measure the time elapsed since the last reading to update the "D" term
  • htim4 (QUADRATURE_TICK_TIMER): Incremental encoder timer configured to read a two-phase quadrature encoder
  • htim6 (GLOBAL_UPDATE_TIMER): 20 Hz timer which triggers a CAN FD transmit (sends motor state)
  • htim15, htim16, htim17 (RECEIVE_WATCHDOG_TIMER_[0,1,2]): FDCAN watchdog timer that needs to be reset every time a message is received