SOLID Learning Robot – Stepper Motors

ANALYSIS: Stepper motors provide a more expensive option that is very precise at the cost of increased complexity (more things needed and more control outputs consumed) and much higher power demands, best suited to fixed robotic designs that need incremental repeatable control over a large span and that allow for additional components and circuits.

Standard Stepper Motor

The most precise type of actuator for our SOLID Learning robots is the Stepper Motor, which can be found in printers, floppy drives and some instrument gauges and is available through online electronics suppliers.

A variety of Stepper Motors from Pololu

Available in a variety of sizes and formats, stepper motors have the highest electrical current requirements of all our actuator options so are best used for robotic designs attached to a continuous power supply rather than for battery-driven independent robots.

An example of circuit power activation for a single step in a Stepper Motor

Stepper motors have no continuous ability to operate, but rely on a series of individual steps conducted through sequential electronic switching to move forward or backward a discrete unit (individual step deflection varies by motor design).

Stepper Motor connected to a lead screw for linear movement control

This sequential control allows very precise movements across a large range using pulley/belt combinations or lead screw designs.

A simple RepRap 3D Printer

Stepper motors are best suited to fixed robotics such as CNC systems and 3D Printers like the MakerBot or RepRap that some SOLID Learning educators may create, all of which remain in place and can easily be served by electrical grid power sources.

A Basic Stepper Motor driver curcuit for 4 TTL outputs

Due to the current requirements, additional components are necessary to drive stepper motors using 5V DC TTL control circuits. Control requires coordination of all four coils and so consumes four output channels for each stepper 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 a stepper motor. The general purpose motor control shield shown here provides control for two DC motors or a single stepper motor.

Pololu's spealized <strong>Stepper Motor</strong> driver

Most stepper motors will rely on a specialized stepper motor driver like the one shown here from Pololu, five of which can be seen on the RAMPS board for a RepRap printer below. These stepper motor drivers transform two channels of control output into the appropriate four-channel sequenced output needed to move a stepper motor forward or backwards.

Fully populated RAMPS board showing five Pololu stepper motor drivers

Summary for Stepper Motors:

  • Price: Expensive ($15 and up) plus motor drivers ($13 and up)
  • Availability: Sourced from surplus printers, floppy drives, electronic suppliers
  • Control: Requires a motor controller or stepper driver for control by TTL logic outputs
  • Operation: Incremental steps
  • Outputs: Four (4) for each motor, Two (2) for each motor controller or stepper driver
  • Caveats: Cannot operate without logical control and consume power even when immobile

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