Rusty Robots

The robot: front view

The robot: side view

Clearly unstable ...

The system model

Inverted pendulum

Accelerometer

Measures proper acceleration

MPU9250

Tilt from gravity

gyroscope

Measures angular rate (degrees per second)

MPU9250

Sensor fusion

Combine data from independent sensors to reduce uncertainty.

Motors: H bridge

TB6612FNG

H bridge: direction

16 possible states but only 4 are used: open, brake and the two above

H bridge: speed

Pulse Width Modulation (PWM)

PID control

• y(t) = measured tilt angle
• u(t) = PWM duty cycle & direction
• r(t) = desired tilt angle (set point)
• e(t) = error

Stable

Unstable

Motion

Differential steering

Spin the wheels at different speeds

Configuration

Board connections

embedded-hal traits

Code reuse: Write once, use everywhere

• Implementers (platforms)
  • stm32f103xx-hal : STM32F103xx microcontrollers
  • linux-embedded-hal : Raspberry Pi and other SBC
• Drivers
  • mpu9250 : Acceloremeter + gyroscope + compass
  • mfrc522 : RFID tag reader / writter
  • And many more to come!

Communication

HC-06: UART <-> Bluetooth

Concurrency

Real Time For the Masses (RTFM) framework for multitasking

• Periodic task (512 Hz)
  • Read sensors
  • Update Kalman filter
  • Update PID controller
  • Log data
• Rx task
  • Parse received frame
  • Update PID gains

Miscellany

CPU usage

21% CPU @ 64 MHz, no FPU, control loop @ 512 Hz