Are the Servos Centered?

The cyber:bot robot's drive motors are called Continuous Rotation Servos.  If you received your robot preassembled, these servos might need to be re-centered before moving on to navigation activities.

  • If you just followed the directions in the Build your cyber:bot tutorial, you will have already centered your servos, and you can skip to the next page: Servo Direction
  • If you were just given an assembled cyber:bot to use, the servos might need to be re-centered. Use the test below to find out.

Test if the servos are centered

Before running this test, double check the battery and servo connections.

  • Make sure that the:
    • Servos are plugged into the servo ports
    • Battery pack is loaded with batteries
    • Battery pack is plugged into the cyber:bot board
    • The jumper is set for the type of batteries you are using

  • Set the 3-position switch on the cyber:bot board to Position 1.
  • Make sure the cyberbot.py module is added to the Project Files (see Add modules to your micro:bit).
  • Enter and save both_servos_stay_still.py.
  • Make sure to include the line from cyberbot import *.
  • Flash both_servos_stay_still.py into your micro:bit.
# both_servos_stay_still.py

from cyberbot import *
 
bot(18).servo_speed(0)
bot(19).servo_speed(0)

If a servo has not yet been centered, or if its center setting has drifted, it might turn, vibrate, or make a humming noise when your script tells it to stay still.

      • Set the cyber:bot robot’s PWR switch to 2, to provide power to the servos.  
      • If both servos stay still, it means they are both centered, and you can skip to the next page: Servo Direction.
      • Any servo that hums, vibrates, or turns in response to this test will need to be re-centered by following the instructions below.

      If one or both servos need to be re-centered:

      Tools You Might Need

      If the Procedure checklist says to remove the servo from the cassis, use these tools that come in the cyber:bot Robot kit:

      (1) Parallax screwdriver, or a different Phillips #1 point screwdriver with a 1/8″ (3.18 mm) or smaller shaft.

      (1) Parallax Combination Wrench (#700-10025), or a 1/4" combination wrench.

      Procedure

      • Check the part of the servo case where the 3-wire cable comes out.  There should be a small round access hole very close to it.
      • If that access hole is close to the battery pack, the servo will need to be disconnected from the chassis.
        • Unscrew the screw in the center of the wheel.
        • Pull the wheel away from the servo to pull it off the output shaft.
        • Unscrew the four screws/nuts that hold the servo to the chassis.
      • If the access hole is instead closer to the front of the cyber:bot, the servo will not need to be disconnected.
      • Complete the Are the Servos Centered? activity, and come back here when you're done (and then continue to the next page).