TWiT Throwback (Video)

Know How... 209: Servo Motor vs. Stepper Motor

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We show how to build a pan and tilt for your camera using stepper motors and an Arduino.

Servomotor vs. Stepper Motor in a Servo Mechanism

Servomotor:

  • A servo is a device that uses a motor with few poles (4-12+) along with some kind of feedback to move a shaft to a particular position.
  • In the case of the servos we're accustomed to using, a simple potentiometer connected to the gearing allows us to put a servo in a particular position.

    • Stepper Motor:

    • A stepper motor is built on a multi-phase motor, with a large number of poles, (50-100+) that moves in "steps"
    • These steps are made by pulsing the various phases of the motor to achieve rotation
    • Stepper motors are usually NOT used with feedback, instead counting on their inherent angular position (created by the way the coils and magnets are laid out in the can) to "step" to particular positions.

      • Pro/Cons:

      • Stepper motors offer more torque at low speeds AND offer "holding torque" because of its inherent angular position.
      • Stepper motors tend to be cheaper
      • Stepper motors can be used without a position encoder
      • Stepper motors lose as much as 80% of their initial torque at 90% speed
      • Stepper motors are slow and not good at accelerating an opject
      • Because they have no positional feedback, it's possible to miss a step
      • Stepper motors suffer from vibration and resonance problems (annoying whine)

        • Servos can move much more quickly (up to ~2,000rpm)
        • Servos have more torque at high speed
        • Servos are more efficient
        • Servos don't vibrate as much as stepper motors
        • Servos require complicated feedback and drive circuitry
        • Complicated gearboxes (prone to destruction)
        • More expensive

          • Now... let's take a look at OUR Stepper Motor!

          28BYJ-48 Motor + ULN2003 Driver

          Important Specs:

          • 5 Volts
          • 4 Phase
          • Stride Angle: 5.625
          • Speed Variation Ratio: 1/64

            • What does this tell us?

            1. This will work on the same 5V power source we're using for the Arduino
            2. A "stride angle" of 5.625 gives us 64 steps for a full rotation of the shaft. (360 / 5.625 = 64)
            3. It is down-geared 64 times: That means the motor shaft has to spin 64 times for every time the stepper shaft rotates once.
            4. This means we have 4096 steps for full rotation of the stepper shaft: (360 degrees / (5.625 / 64) = 4096)

              5. OK... let's build!

              Parts List:

              Arduino of your Choice

              Stepper Motor and Driver

              5V Power Supply

              Breadboard

              What's What?

              • Show the power input and switch
              • Show IN1-4
              • Show the motor connector

                • Let's put it together!

                1. Connect the motor to the driver board
                2. Attach a 5V power supply to the power-in on the driver board
                3. Connect IN1-4 to Arduino digital pins 4-7
                4. Connect power to the Arduino

                  5. That's It!

                  Let's Program!

                  The Code is Available at the link below:

                  https://www.dropbox.com/s/ty21w4exs6ruka9/KH209_Stepduino.zip?dl=0

                  The STL Files for our 3D Printed frame is at the link below:

                  https://www.dropbox.com/s/jfpn6furd033irn/KH209_Stepduino_STL_Files.zip?dl=0

                  These show notes have been truncated due to length. For the full show notes, visit https://twit.tv/shows/know-how/episodes/209

                  Hosts: Fr. Robert Ballecer, SJ and Bryan Burnett

                  Sponsors:

                  • ifixit.com/twit enter code KNOWHOW
                  • digitalocean.com - promo code: KNOWHOW

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