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Practice Pet: Llama

Before starting your robotic animal, you are going to build a practice animal. The goal of building this animal is to practice using a crankshaft and a linkage. Don’t worry about decorating your llama. Focus instead on making these mechanisms sturdy and functional. As you build, think about how you can include mechanisms in your petting zoo animal.

Learning Objective: Use two mechanisms to transform rotation into other types of movement.



Building the Tail


Materials

Small box, like a shoebox
Cardboard
Gear motor
Plastic block adaptor for gear motor
Screw for gear motor
1 brad
Pom-pom

.

  1. Glue the side of the gear motor to one or two small pieces of cardboard.



  2. Place the gear motor in the box and mark where the rotating portion of the motor should pass through a box. Make a hole there. Then glue the gear motor in place. To mount the motor securely, be sure to put glue both on the cardboard below the motor and on the side of the motor that faces the side of the box. Do not put glue on the rotating part of the motor. 

  3. Create a strip of cardboard with a hole in one end. This will be the tail! Use the brad to connect the tail to the plastic block adaptor, which is the crankshaft. 

  4. Use the screw to connect the plastic block adaptor to the gear motor. If necessary, remove some cardboard so that the motor can turn. When the box is placed on the table, the plastic block adaptor should be able to turn 360° without hitting the table (this is why we put the cardboard underneath the motor in Step 1). 

  5. Use cardboard to create a retainer for the tail. The retainer should allow the tail to move up and down (and move a little side to side). Glue your pom-pom on the tail! 

  6. Use Scratch to test the tail. When the gear motor rotates, the tail should move up and down and side to side. How would the movement change if the crankshaft (the plastic block adapter) was larger? What would happen without the retainer?.


Building the Neck


Materials

Servo motor
Four linkage pieces
4 brads
Cardboard
Picture of a llama head

  1. Before you begin to build, plug the servo motor into the Hummingboard board and use Scratch to set it to 90°.  
  2. Remove the white plastic circle from the servo motor. In the side of the box opposite the tail, make a hole for the rotating part of the servo motor. Glue the servo motor inside the box so that the rotating portion passes through the hole. 
  3. Right now, there is only a little hot glue holding the servo motor in place. The motor is not mounted securely. Use cardboard to create mounting brackets for the motor.
  4. Use the linkage pieces and the brads to construct the linkage shown below. What happens when you move the bars that form the ‘X’ in the linkage? 
  5. Reattach the white plastic circle to the servo. Glue the bottom bar of the ‘X’ in the linkage to the white plastic circle. The brad should be positioned over the screw in the white plastic circle (but try not to get glue on the screw). 
  6. Glue the other arm of the ‘X’ to the box. You will need to place ~2 small pieces of cardboard underneath it to account for the space occupied by the white plastic circle and the lower arm of the ‘X.’ Why do you think we need to attach this arm of the ‘X’ to the box?
  7. Glue the picture of the llama head to the top of the neck. Now your practice llama should look like the picture at the beginning of these instructions.
  8. Test the neck using Scratch. You should be able to move the servo motor between 60° and 120° (maybe farther). Why do you think we set the servo to 90° in Step 1?
  9. Write a sequence using both the tail and the neck. Then add a sensor to control the movement of the tail and neck.
  10. When you are done, customize your llama! Add a sensor to control it!
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