Thinking about Forces

There are a lot of good websites that discuss forces and more specifically Newton's Laws.  Here is one example:  http://www.cet.edu/?cat=online_learning&page=46.  It did take my computer a little while to load the items, so be patient.  :) 

When designing, building, and testing robots, its good to think in terms of forces.  A force can be thought of as a push or a pull.  Motion results from forces.  Since we want to control the movement of our robot, it makes sense to understand the forces acting on our robot.

Here are some examples of forces:  Weight is a force pulling down due to gravity.  Friction is a force that opposes motion.  And there are more.  What other forces can you think of?

How can thinking about forces help our robot design?  Well, here is an example.  Balanced forces cancel each other out.   This is why having a symmetrical design, or having a balanced weight distribution is important. Balanced forces will help your robot to go straight.  If your robot is going crooked, basically there are unbalanced forces acting on your robot.  People often talk about the things that cause robots to go crooked, like uneven wear of your wheels.  This would be when one wheel is more worn than the other.  The older, more worn wheel will be smoother, perhaps slipping at times.  It will produce a smaller frictional force.  The newer wheel, with a good tread, will grab the surface more, resulting in a greater frictional force.   So the difference in wear results in a difference in the frictional forces.  These  forces being different are unbalanced forces, and cause a turning motion in the robot.

This idea is similar to a balance or scale.  We have a math balance, which I like to use to illustrate this point.  If you want the balance or scale to be level, the forces on both sides must be equivalent.  If one side has a larger weight (weight is a force pulling down), it is going to turn about the midpoint or balancing point.  This concept is true for our robots too.  Our robots have a balancing point.  It is called the center of mass or center of gravity.  For symmetrical shapes it is in the center.  If you apply an unbalanced force on one side of the robot, it  will turn about its balancing point.   If you apply the force at the balancing point, no twisting or turning  will take place.  It will move forward.  If you apply two equal forces, one on each side, the robot will go straight. 

 In college, mechanical engineering students draw "free body diagrams", which show all the forces acting on an object.  Forces are vectors, so they have both a direction and a magnitude. On the free body diagram they are drawn as arrows.  Math is used to combine the forces into one resultant force.  Using Newton's Laws we can calculate the direction it will be moving and its acceleration.  Newton's Laws give you some principles or truths that you can use in designing and troubleshooting your robots. 

Summarizing, movement and motion result from forces.  So understanding forces will help you in your robotics work.  Spend some time reading about Newtons Laws, Forces, and Mechanics. It might take some time for it all to sink in.  That's OK.  The sooner you start thinking about it, the sooner it will all make sense. 

Here is another site to get you started on your study of motion and forces. 
http://www.physics4kids.com/files/motion_intro.html