Build a robot – Part 5: Finding the right motor driver

After mounting and attaching the Arduino and ultrasonic sensor it is time to spend some thinking time about the driving concept. At first we have to look at some technical specifications of the two dc motors:

  • no load current: 200mA (max)
  • rated current: 1200mA (max)
  • stall current: 4500mA (max)
  • working voltage: 9V

The dc motor needs 9 Volts to operate. The three other specifications are describing the following,

  • no load current
    • the minimum amount of Ampere the motor will consume
  • rated current
    • the amount of Ampere the motor consuming on full speed
  • stall current
    • the amount of Ampere the motor consuming when blocked e.g. by too much load or driving against an non movable obstacle

Only by the fact that the motor requires 9 Volts the Arduino itself cannot be used to power the motor. The GPIO pins are only serving a maximum of 5 Volts. Additionally the maximum output of 20 mA is also not usable. Therefor a suitable motor driver has to be used. Major features are:

  • 6.5V to 45V motor power voltage
  • Up to 5.5V logic level on IN pins
  • 565mΩ Typical RDS(on) (high + low)
  • 3.6A peak current
  • PWM control
  • Current limiting/regulation without an inline sense resistor
  • Undervoltage lockout
  • Overcurrent protection
  • Thermal shutdown

You see, the Ardafruit DRV8871 has some specs which are suitable to control one dc motor. In total we have to use two of them. A complete and easy documentation of installation and usage can be downloaded here.



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