Big rover robot platform – Part 2 – Better Control

Brushed DC motors are inherently hard to control accurately compared to modern BLDCs, especially at low speeds.

Outline of what we will do:

  • Linearize the output voltage of our H-Bridge
  • Create an open-loop speed controller
  • Add a closed loop speed controller on top

Linearize H-Bridge Output Voltage

A prerequisite to predictable motor behaviour is a predictable voltage source. Our H-Bridge module does not actually output a voltage that’s proportional to the duty cycle of the PWM-signal we use to control it. This is due to a protection feature that introduces some dead time when switching, to avoid shoot-through conditions. It’s great to have it, but we want this detail to be transparent to our control loop.

To achieve that, we simply map the full range (0…100%) to the ranges of approximately linear behaviour (9.2…89%), both for the negative and positive output ranges.

Create an open-loop speed controller

Let’s keep it brief: We want to control rotational speed n, which is proportional to back-emf e.

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