SOLID Learning Robot – DC Motors

ANALYSIS: DC motors provide a relatively-inexpensive option at the cost of increased complexity (more things needed) for elementary robotics but lacks precision or fine control for higher robot studies without additional components and circuits.”

Simple DC Motor with two-wire connector

The simplest type of actuator for our SOLID Learning robots is the standard DC Motor, which can be found within many common motorized toys and is available from electronics suppliers. Very small DC motors can be found in pagers and smartphones to provide the non-audible Buzz alert, while much larger versions are called Starters in automobiles. When coupled with a gearbox, reduced speed can be traded for increased torque (power) at the cost of a slightly larger motor assembly. This adds weight and overall motor size in our robots.

DC Motor with Gearbox attached for increased torque

The DC motor is very simple in operation – if a current is passed through a DC motor it turns one direction and reversing current flow will also reverse motor direction. Motor speed is controlled by varying the voltage used to energize the motor. When DC motors are started and stopped, they can generate high current spikes due to magnetic field formation and collapse. This requires additional components to protect sensitive TTL circuitry in our control electronics. A resistor and capacitor can be put in parallel to the motor in order to reduce potential spikes, while a transistor is necessary to drive one-directional high current or voltages greater than the 5V DC provided by our control circuits.

Four transistors forming an H-Bridge for bidirectional control of DC loads

Because our robots will need bidirectional motor control (moving both directions), we need a more complex circuit for two-directional control of the power flow – typically an “H-Bridge” created from two PNP and two NPN transistors. Using only two of our control circuit’s outputs, we can control a bidirectional power flow to the DC Motor.

An Arduino-comparible Motor Control Shield for 1 or 2 DC motors

One way to avoid consuming all of our available output channels in complex robotic designs is to use a Motor Controller board to handle all of the internal operations. The motor control shown here provides bidirectional control through dual H-Bridges for up to two DC motors.

Summary for DC Motors:

  • Price: Inexpensive ($2 and up)
  • Availability: Sourced from surplus pagers, toys, electronic suppliers
  • Control: Requires a motor controller for bidirectional control from TTL logic outputs
  • Operation: Continuous
  • Outputs: Two (2) for each motor, Two (2) for each motor controller
  • Caveats: Additional parts needed to vary speed of rotation and determine the distance of travel

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