For a robot to be consistent, it must go straight. As my teams build, they can earn badges for performing robot tests. The straight test is simple:
- Program the robot to go straight 4 rotations using a motor power starting at 30.
- Run the robot and observe if it goes straight.
- Record the results.
- Repeat with motor speeds of 50, 70, 100.
The Capital Girls, had a build meeting today with four out of the ten girls. Their goal was to finish the robot by adding a third wheel, bumpers and sensors. After 2 hours, they managed to just add the wheel and bumpers.
The third wheel was a challenge, and a discussion erupted about using fours wheels. In the design meeting, not everyone agreed on three wheels but majority ruled. The build team elected to following the design plan and extended the bearing wheel from the EV3 base robot so the robot was level.
As the meeting was ending, the girls ran a straight test. The robot went sort of straight but waddled badly. The waddle was very obvious.
After everyone left, my daughter asked if she could try a four wheel design. I said yes, with the understanding she had to keep the bearing third wheel component so she could share both designs with the entire team and let them decide.
After her build, we did the straight test and, as you might have guessed, fours wheels ran straight as an arrow.
After her brother saw her design, he accused her of copy his team’s design. Being who she is, she said, “Yes, we copied your design.” She had not even seen his design – siblings!
For the design process, each team used the Robot Design Guide and had similar answers but different rationales. The boys wanted a three-wheel robot for fast pivot turns. The girls wanted a smaller robot. As of now, they each have 4 wheels designs but got there for different reasons and have different chassis designs. The Code Crackers wanted to tackle the debris challenge and thought four wheels would make the robot more stable going over the obstacles. The Capital Girls were going to ignore the debris challenge but could not get a three-wheel robot to go straight. Below are both teams’ designs. You might notice the back wheels for both teams do not have a tire, just a rim. When doing design planning, there are two wheel tests the teams perform to understand the speed and traction characteristics of the wheel options. The tests teach two wheel concepts: 1) the bigger the wheel, the faster it will go, and 2) the more contact surface and wheel material, the more traction/friction. This learning exercise, along with the straight and balance tests, guides the robot design. What I like about the exercises is that they guide the design process through testing and exploration, helping the teams determine why, not just what. To learn more about the robot testing, download our Robot Design Guide.
Capital Girls (Left) | Code Crackers (Right)