The Basics of Mechanical Engineering
If you go to engineering school, you will be swamped immediately with an incredible amount of math and physics. I will not teach you much (if any) math here, but a basic understanding of how systems work so you can begin the steps of design, and if you have the time and understanding, you can tackle the mathematical hurdles on your own.
Simple Machines​
There are a small group of mechanisms on which everything else is based. These are simple systems that are easy to understand and build.
Each definition is the first paragraph of the Wikipedia article on each
There are 6 simple machines:
Pulley​
Definition
A pulley is a wheel on an axle or shaft that is designed to support movement and change of direction of a taut cable or belt, or transfer of power between the shaft and cable or belt. In the case of a pulley supported by a frame or shell that does not transfer power to a shaft, but is used to guide the cable or exert a force, the supporting shell is called a block, and the pulley may be called a sheave.
Pulleys are not terribly common in FTC because it is hard to control the swinging and consistency of a hanging string, with one notable exception. Pulleys are used to make linear slides actuatable, where by pulling on the string, the slide extends. Pulleys are also occasionally used to increase torque, but it is rarely successful, and even more rarely necessary. Gears are a better choice.
Lever​
Definition
A lever is a simple machine consisting of a beam or rigid rod pivoted at a fixed hinge, or fulcrum. A lever is a rigid body capable of rotating on a point on itself. On the basis of the locations of fulcrum, load and effort, the lever is divided into three types. Also, leverage is mechanical advantage gained in a system. It is one of the six simple machines identified by Renaissance scientists. A lever amplifies an input force to provide a greater output force, which is said to provide leverage. The ratio of the output force to the input force is the mechanical advantage of the lever. As such, the lever is a mechanical advantage device, trading off force against movement.
Levers are extraordinarily common in nearly everything, and FTC robots are no exception. They are extremely helpful because they allow a rod to rotate in a preset direction while being properly supported and are able to remain stable and hold weight.
Levers also provide a mechanical advantage by the distance from the point of actuation to the fulcrum.
Credit: Shawn S. on Flikr
You can see how the lever is holding up the car on one side, and has ropes that allow people to pull and lift the car on the other side. If you have ever been to COSI in Columbus, Ohio, you have probably experimented with this and found that it is not in fact difficult to lift the car by hand because of the mechanical advantage offered by the lever. This is applicable to FTC as we can use them to manipulate things within our robots.
Wheel and Axle​
Definition
The wheel and axle is a simple machine consisting of a wheel attached to a smaller axle so that these two parts rotate together in which a force is transferred from one to the other. The wheel and axle can be viewed as a version of the lever, with a drive force applied tangentially to the perimeter of the wheel and a load force applied to the axle, respectively, that is balanced around the hinge which is the fulcrum.
Wedge​
Definition
A wedge is a triangular shaped tool, and is a portable inclined plane, and one of the six simple machines. It can be used to separate two objects or portions of an object, lift up an object, or hold an object in place. It functions by converting a force applied to its blunt end into forces perpendicular (normal) to its inclined surfaces. The mechanical advantage of a wedge is given by the ratio of the length of its slope to its width. Although a short wedge with a wide angle may do a job faster, it requires more force than a long wedge with a narrow angle.
The force is applied on a flat, broad surface. This energy is transported to the pointy, sharp end of the wedge, hence the force is transported.
Upon reading the definition, you will probably identify very few applicable uses of wedges to FTC Robotics, but think of intake mechanisms, where you have to collect something off the ground. Most likely, your solution is either a bunch of wheels or belts pulling upwards, or a wedge riding close to the ground that the objects are simply pushed onto.
Inclined Plane​
Definition
An inclined plane, also known as a ramp, is a flat supporting surface tilted at an angle, with one end higher than the other, used as an aid for raising or lowering a load. The inclined plane is one of the six classical simple machines defined by Renaissance scientists. Inclined planes are used to move heavy loads over vertical obstacles. Examples vary from a ramp used to load goods into a truck, to a person walking up a pedestrian ramp, to an automobile or railroad train climbing a grade.
It is important to understand the difference between a wedge and an inclined plane. A wedge is actively used and actuated, whereas an inclined plane is passive and often serves as just a shield or a ramp.
Inclined planes are not common on basic robots, but as you begin to deal with more advanced robots, inclined planes are used passively to make sure things can slide off the robot and not get trapped in the robot.
Screw​
Definition
A screw is a mechanism that converts rotational motion to linear motion, and a torque (rotational force) to a linear force. It is one of the six classical simple machines. The most common form consists of a cylindrical shaft with helical grooves or ridges called threads around the outside. The screw passes through a hole in another object or medium, with threads on the inside of the hole that mesh with the screw's threads. When the shaft of the screw is rotated relative to the stationary threads, the screw moves along its axis relative to the medium surrounding it; for example rotating a wood screw forces it into wood. In screw mechanisms, either the screw shaft can rotate through a threaded hole in a stationary object, or a threaded collar such as a nut can rotate around a stationary screw shaft. Geometrically, a screw can be viewed as a narrow inclined plane wrapped around a cylinder.
We don't see screws (the simple machine, not the piece of hardware) in FTC often because they are usually extreme overkill. Screws are used in non-hydraulic linear actuators and are great at taking a low-torque rotary force and turning it into an extremely high-torque (but very slow) linear force.