Designing with Momentum in Mind
How Physics can Affect Competition Robots
When designing a robot for VEX Robotics Competitions, you must remember that any motor will be fighting against the robot's inertia whenever the robot is running. Inertia is an object's resistance to changes in its velocity. Inertia is increased as the object's mass and therefore its momentum are increased. This means if you add mass to your robot and make it heavier than it has to be, the motors will not be as effective in changing the robot's velocity! Therefore, you should try to use as light and as few materials as possible if you want to maximize the motors' efficiencies.
On the other hand, running a light robot very quickly can also lead to difficulties. If you are trying to make precise and accurate movements in the course of a competition, you may need to ease off of the power by reducing the velocity during your movements.
Let's explore the idea that the momentum of two colliding objects predicts what will happen after they collide. This is an important factor to consider when developing competition projects because you want your robot to move as fast as possible. You also want to have as many components as possible built into the robot that will give it an advantage for manipulating and collecting during the game.
Momentum is the amount of motion that an object has and is determined by the moving object's mass and velocity. So, a competition robot with all of its components can be heavy and moving as fast as possible. Therefore, its momentum is very high. This is when you need to consider what happens when it comes into contact with parts of the field or other robots.
Look back at your table from the Exploring Velocity activity. You tested the transfer of energy during collisions by setting different velocities for the robot and driving it forward until it hit the ball. You should have noticed that higher velocities set for the robot pushed the ball farther after a collision than lower velocities did. This is an obvious effect of the robot's momentum because the mass of the robot remained the same but the velocity increased and therefore, its momentum increased.
Something important to consider about that test is that the ball was not moving. It had a velocity, a momentum, and an acceleration of all zeros before the robot collided with it. Importantly, its mass was likely far less than the robot's mass. After the collision, its acceleration and therefore its velocity and its momentum all increased. How fast the ball's velocity was after the collision depended in part on the mass of the ball. Lighter balls accelerate and move faster. If your class used a ball with more mass, imagine a bowling ball, the ball might have moved slowly and not very far after the collision.
Again, this is important to consider when planning for a competition because you can break parts of the field, parts of your robot, or parts of other robots if the robot's momentum is too high. Imagine if your robot had a high velocity and crashed into an object that couldn't roll away like the ball in the previous activity. That object could have been broken by the impact forces (energy) of the collision.