Wire

Wire

Why Wire?

In circuits classes, you learn about the concept of nodes. Nodes are parts of a circuit which exist all at the same voltage. Wires are what we use to connect two or more terminals to form a node. Wires let us quickly and easily extend nodes to provide power from one location, such as a battery to another location, such as a motor.

Wire Gauge

Unlike in circuits or electronics classes, in the real-world wire has resistance. In physics you'll learn the exact formula for calculating resistance of a given wire, but we don't especially need that. Instead, stick with the practical knowledge that the thicker the wire, the lower the resistance of that wire, and the longer the wire, the higher the resistance. Generally we will use copper wire, but it can be useful to know that aluminum can be used instead of copper. However for the same diameter and length of wire, aluminum has 60% more resistance than copper.

Wire gauge is a measure of the diameter of a wire. We will use the American Wire Gauge (AWG) as the "units" for measuring diameter. Confusingly, the larger the gauge of a wire, the smaller the diameter. In other words, 0 AWG wire is very large while 30 AWG is very small. Use the following table as a guide for the appropriate wire gauge for a given current. An appropriate gauge will limit the power losses and heat induced in a wire by a given current. It will not hurt to use a larger wire than is necessary, but usually the smallest gauge wire possible should be used because smaller wire is easier to work with.

Current (A)	Minimum Wire Gauge
Signal	28 AWG
2	24 AWG
5	22 AWG
20	18 AWG
30	14 AWG
40	12 AWG
100	6 AWG

We will generally simplify this chart and use only 6, 12, 18, and 20/22 AWG. 6 AWG is used for any wire that carries the entire battery current. 12 AWG is used for large motors such as CIMs, BAGs, or Falcon 500s. 18 AWG is used for lower power motors, such as those in most linear actuators. 20 or 22 AWG is used for signal level wires, such as for CAN Bus or potentiometers. Any wire below 22 AWG becomes extremely difficult to work with because it is so small.

Power wiring vs Signal wiring

Power wires are wires which provide electrical power, while signal level wires carry electrical signals. This distinction is important because the decision of what wire to use is very different for the two types. Power wires should be thick enough to carry the necessary current, whereas signal level wires carry essentially no current. Signal level wires require additional considerations for ensuring signal integrity. See Cable selection for CAN Bus as an example.

Types of wire

Generally, all wires can be divided into two major categories: solid and stranded. You can find wire of any gauge as either type. Solid core wire, as the name suggests, is a single solid cylinder of metal. Solid core wire is not flexible and will tend to break if bent back and forth due to metal fatigue. Stranded wire is made up of any number of smaller "strands" or wires to form one large wire. The number of strands corresponds directly to how flexible a wire is, with higher strand count wire being more flexible.

We prefer to use high strand count wire because it's flexibility makes it easier to work with as it is routed around the robot. Low strand count or solid core wire should not be used because it is likely to break from the vibration of the robot moving or from the process of installing it. You are unlikely to find solid core wire > 18 AWG but are very likely to find it used for bread boarding. This bread board wire should not be used on the robot.

Cable

A cable is made up of multiple wires, referred to as conductors. Each conductor is electrically isolated from each other conductor. Ethernet cables are an excellent example of a cable. Cable is convenient for when multiple wire need to be routed from one place to another, such as to the screen and button of one of our electrical boxes. Cable is not usually used for power wires because cable is not usually made for large wires. You can also create your own cable by simply twisting wires together.

Buying wire

Wire can be bought from many different sources. Ensure when purchasing wire that you are buying copper wire and not cheap aluminum wire. Search for "silicone flexible wire" and you will get the best results. Silicone refers to the type of plastic used as insulation. Flexible refers to the high-strand count. You can find surprisingly flexible wire of almost any gauge of this type.