The Motor Controllers

by Web FishMar 16, 2013 @ 12:34pm

Controls the direction and power of the propulsion pods. Translates the central processor decision making and the battery power into mechanical movement.

  • Current selection: Pololu Simple Motor Controller 18v7
  • Status: Undecided (under testing)

  • Criteria: Max current handling, standard I/O, small physical footprint, thermal footprint, cost 
  • Finalists: Pololu RoboClaw 2x5A Motor Controller, Arduino Motor Shield R3, SeeedStudio Grove Motor Driver 
  • Main decision factors: High sustained / peak currents, cost, standard serial bus interface

 (click image for larger view) 

Spec highlights:

  • Simple bidirectional control of one DC brush motor.
  • 5.5 V to 30 V operating supply range.
  • 7 A maximum continuous current output without a heat sink
  • Four communication or control options:
    • USB interface for direct connection to a PC.
    • Logic-level (TTL) serial interface for direct connection to microcontrollers or other embedded controllers.
    • Hobby radio control (RC) pulse width interface for direct connection to an RC receiver or RC servo controller.
    • 0–3.3 V analog voltage interface for direct connection to potentiometers and analog joysticks.

 

Caveats:

  • Still unclear if we will use UART or PWM to control the boards. We are using 2 pins either way;
  • If using UART, both boards will be chained;
  • Unclear if hat signature will be an issue until we mount in the navionics bay with the rest of the electronics modules;

 

The Compass

by Web FishJan 6, 2013 @ 02:03pm

Provides information about about momentary vessel orientation with respect to the earth's magnetic field (compass), as well as earth's gravitational field (accelerometer). Basic navigation instrument.

  • Current selection: LSM303DLHC 3D Compass and Accelerometer
  • Status: Finalized

  • Criteria: Sensitivity, standard I/O, small physical footprint, cost 
  • Finalists: Sparkfun HMC6352, Sparkfun LSM303 Breakout Board, Pololu LSM303DLHC 3D Compass and Accelerometer
  • Main decision factors: Cost, standard I2C bus interface

 (click image for larger view) 

Spec highlights:

  • Dimensions: 0.5" × 0.8" × 0.1" (13 × 20 × 3 mm)
  • Weight without header pins: 0.6 g (0.02 oz)
  • Operating voltage: 2.5 to 5.5 V
  • Supply current: 10 mA
  • Sensitivity range (configurable):
    • Accelerometer: ±2, ±4, ±8, or ±16 g
    • Magnetometer: ±1.3, ±1.9, ±2.5, ±4.0, ±4.7, ±5.6, or ±8.1 gauss

 

Caveats:

  • Still unclear how well (if at all) the tilt compensation will work in a constant motion (sea waves) environment;
  • Unclear whether we'll be able to use built-in accelerometer to determine vessel orientation up/down (current flip status) - again, due to constant acceleration changes from riding surface waves;