Playing With Gears

This chapter in the LEGO robotics book overviews the importance of using gears to improve the functionality of your robot and to ensure proper usage of gears.
First off, the main theory behind a gear is that by using a gear to turn another gear of a different size, you can either multiply the force behind that second gear, or greatly accelerate the speed at which that gear travels. In the above example, the gear being used to turn the other gear is known as the driving gear, and the gear being turned is known as the driven gear. The forces being outlined in the above example are essentially torque, and what is known as angular velocity, or 'speed'. Torque is a product of force and distance and basically is the amount of kick or driving power behind a gear. Angular velocity is the rate at which your robot will cover distances.
When wanting to increase torque on a robot, the driving gear would have to be smaller (have fewer teeth, ie. little pegs) than the driven gear and vice versa for the driven gear. So based upon this concept one would think that you should just add as many gears as possible to magnify your robots capabilities. However, this is where another catch is met: a force called friction. Friction is the amount of force being transferred between the teeth of your gears; and consquently, having more gears means more teeth and thus more friction. Having too much friction can damage the robot, gears, and whatever motors are driving it; thus a proper balance must be found.

There are also many types of gears that can be used for several different situations. For example, a gear known as a knob wheel (four rounded teeth) is a gear that is specialized in providing more torque as its larger surface area on the teeth allows more energy to be transferred. Another type of gear, known as a clutch gear is essentially a 'safety' gear that locks down when too much force is applied to it. This gear is useful in protecting the rest of your gears and robot in case too much force is exerted.

In addition to just connecting gears to gears; gears can be connected using pulleys and chains. Using pulleys and chains allows you to connect gears that would normally be too far away to just stick in a bunch of other gears to connect. Pulleys also have the advantage of being much quieter than gear connections. The difference between pulleys and chains lies in the forces they are better suited to dealing with. Pulleys, using belts tend to have very little grip on the gears and as a result produce very little torque, which is good if you are going to for angular velocity. Chains however are composed of individual links and have the most amount of grip on the cogs on the gears. This means that they produce the most torque and are relatively poor for use when trying to achieve high angular velocity.