Try the Continuous Servo

Warning: While the board is powered and the wires are connected in the Arduino board, do not to let the red and black wires touch. Students need to be especially careful if the exposed wires are bent and might touch when inserted in the end of the Servo.

1. Disconnect the white, red, and black wires from the socket of the standard Servo.
    
2. Insert the same white, red, and black wires into the matching sockets of the continuous Servo.
    
3. Notice the Servo is rotating in one direction and then the other.  

STEM Connections

The standard and continuous Servos move very differently, even when given the same instructions from the program you uploaded to the Arduino board. Remember, standard Servos move to specific angles and continuous Servos rotate in either direction at different speeds. Continuous Servos take in the same numbers (0 through 180) as standard Servos, but they interpret those numbers differently. They do not interpret the numbers to be angles, but instead they interpret these numbers as the direction and speed of their rotation.

When translating those numbers into the direction of the rotation, continuous Servos interpret the number 90 as no movement, or stopped.  A number that is greater than 90 is interpreted as rotation in one direction and a number less than 90 is interpreted as rotation in the opposite direction.

When translating those numbers into the speed of the rotation, the closer the number is to 90, the slower the Servo will spin, and the further away the number is from 90, the faster the Servo will spin. Therefore, when the Arduino board runs the line of code “myservo.write(0);”, it will spin fast in one direction and when it runs the line of code “myservo.write(180);”, it will spin fast in the opposite direction.

At the Thinkabit Lab we ensure that students understand that the same code works for both Servos, but the Servos behave differently by doing the following:

• Explain that for the standard Servo, the number inside myservo.write( ); matches the angle it will point to, but the continuous Servo is not as straightforward.

• Draw a diagram to help students visualize the motion of the Servos by drawing a number line from 0 to 180. 

• Ask students, where should we mark and label to represent the number 90. If “myservo.write(90);” is written, this means that the continuous Servo should stop. Please note that the Servo may not stop exactly at 90. Encourage students to determine the number that stops the Servo they are using. The number can be as high as 93 and as low as 87, but always close to 90.

• Shade or draw an arrow to the right of 90 (90 –> 180) and write out which direction it spins. For us, it’s right, or clockwise, but we’ve seen continuous Servos where the opposite is true. Likewise, shade or draw an arrow to the left of 90 (0 <– 90) and write out which direction it spins. The extreme end points, 0 and 180, the furthest points from 90, are the values that make the Servo spin the fastest. If a number is selected that is closer to 90, the Servo will spin slower.

• If time permits, have students experiment with changing their code to make the continuous Servo spin at a slower speed.  Remind students that after changing the code they need to upload the new code.

If you are using the Thinkabit Lab Notebook:
 

Use the diagram and explanation on page 17 to help further explain the motion of the continuous Servo with students.

Servo doesn’t work

1. Check to make sure that the wires are all connected to their corresponding color on the Servo connector.

2. Check to see that the program was successfully uploaded to the Arduino board by looking for the “Done Uploading” message on the Arduino software

3. Check to make sure that the wires are connected to the correct pins on the Arduino board. Remember, Red –> Vin, Black –> GND, and White –> Pin 9.

4. If all else fails, replace the Servo. Note: It is not uncommon for Servos to break after repeated use.