Centering the Servos

Servos are a special type of motor.  They come in two different types: standard and continuous rotation.  Standard servos rotate to a specific point (and stay there) based on the input signal.  These types are widely used in radio controlled (RC) applications.  For the Boe-Bot drive wheels, we’re using the continuous type.

Continuous rotation servos need be calibrated or “centered”.   If a servo has not yet been centered, it may turn, vibrate, or make a humming noise when it receives the “stay-still” signal from the microcontroller.

You will use a small Phillips screwdriver to adjust the servos so that they actually stay still while receiving the “stay-still” signal from the BASIC Stamp microcontroller. We call this centering the servos.

You’ll need the Phillips screwdriver that came with your Boe-Bot kit (Phillips with a 1/8 inch (3.18 mm) or smaller shaft).

  • Launch the BASIC Stamp Editor that you installed earlier on your PC.
  • Connect the USB cable from your computer to the control board.  
  • Place your Boe-Bot up on top of a small box or block so that the wheels are off the ground, and can freely spin without moving the bot.  
  • Set the power switch to position “2”.  This will provide power to the circuit board and to the servos.

  speedLeft = 0
  speedRight = 0
  time = 30000
  GOSUB Wheel_Speeds
  • Click on the Run icon to send this program down into the BASIC Stamp.

Your Boe-Bot may start spinning one or both wheels, in either direction. 

  • Using the small Phillips screwdriver, adjust the screw on the front of each of the servos so that they come to a complete stop.

This short program is sending the “center off” command to each of the servos, and by fine-tuning both of them, they will be completely stopped when this command is received by the servos.

Your Boe-Bot’s servos should now be calibrated and "centered".