Before we can build Simple Bots, it is important to have a rudimentary understanding of how electricity works (or does not). Electricity comes in two forms, AC (alternating current), which is like the power that comes from a wall socket, and DC (direct current), which is like the power that comes from a battery. In the Simple Bots eBook, all of the electricity for bots will be coming from batteries. So, I will only be explaining DC (direct current) electricity in this Instructable.
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When working with DC electricity, there are a few things to keep in mind, but two in particular which you shouldn't forget:
- DC power sources have both a positive ("plus") terminal and a ground terminal.
- In order for any circuit to work, electricity must be able to flow between positive and ground.
The next very important consideration to keep in mind is that electricity must be used.
In other words, there needs to be something wired between positive and ground that adds resistance to the flow of electricity and uses it up. If positive voltage is connected directly to ground and does not first pass through something that adds resistance, like a motor, this will result in a short circuit. This means that the positive voltage is connected directly to ground.
When positive voltage is connected directly to ground, your battery will get painfully hot and, after a while, may do something bad like leak nasty burning chemicals. It may also result in spontaneous combustion of your circuit.
It is very important to prevent short circuits by making sure that the positive voltage is never wired directly to ground.
Note: A switch does not add resistance to a circuit and simply adding a switch between power and ground will create a short circuit. While building Simple Bots, you should always make sure that your circuit has at least a motor between power and ground.
Series and parallel are two different ways that electronic components can be wired together in a circuit.
When things are wired in series, things are wired one after another, such that electricity has to pass through one thing, then the next thing, then the next, and so on.
In this example, the motor, switch and battery are all wired in series because the only path for electricity to flow is from one, to the next, and to the next.
When things are wired in parallel, components are wired side by side, such that electricity gets divided between them and passes through all of them at once.
Now, to put it all together. In this example, the motors are wired in parallel, but the pair of parallel motors, switch and batteries are all wired in series.
So, the electricity is split between the motors in a parallel fashion, but still must pass in series from one part of the circuit to the next.
Note: Electricity follows the path of least resistance to ground. This means, that if you give positive voltage the choice to pass through a motor to ground, or follow a wire straight to ground, it will follow the wire because the wire provides the least resistance. This also means that by using the wire to bypass the source of resistance straight to ground, you have created a short circuit. Always make sure that you never accidentally connect positive voltage to ground while wiring things in parallel.
To work with electronics, we will be using a handful of basic supplies and tools. The electronic supplies mainly include wire, battery holders, switches and motors. You will also need a couple of extra tools that we did not mention in the Simple Bots Tools and Fasteners instructable. If you don't know how to solder, don't worry, we will briefly go over that.
To begin with, we will need battery holders and clips. The standard battery that we will be working with is AA and the standard size battery holders will hold two, three and four AA batteries.
The way the AA battery holders work is that they connect the batteries in series. When connected in series, the battery voltage adds up. So, two 1.5V batteries in series adds up to a 3V power supply. It goes to follow that three batteries add up to a 4.5V power supply and four batteries add up to a 6V power supply.
On occasion, we will also use 9V batteries and connectors.
The next thing we will be using, and a lot of, is 22-gauge stranded wire. You will want to get a spool of red wire and a spool of black wire. Traditionally, red represents power and black represents ground. It is good form to use your wire in this manner, to avoid wiring mistakes and short circuits.
Note: For prototyping, you may want to get a set of alligator clips. These allow you to quickly and impermanently wire things together for prototyping without having to solder them.
Wire strippers are used to both cut wire and easily remove the insulation from around the metal core.
To use them, simply insert the end of your wire into the appropriately-sized groove, squeeze the handle tight, and pull on the longer side of the wire. This should remove the jacket from the end of the wire
Switches come in all shapes and sizes. They can be controlled by levers, buttons, sliders, twisty knobs and even magnets (to name a few). They all fundamentally operate on the same principle. Basically, a switch opens and closes a circuit.
In other words, imagine that you have a complete circuit wired together and it is turned on. Then, imagine that you cut one of the wires in the circuit in half and the circuit turns off. Now, imagine that you touch these two ends of the wire together again and it turns on. Then, you pull them apart and it turns off. You have just created a crude switch.
A simple switch is basically a break in a circuit that can be opened and closed, typically by some sort of mechanical means (like a lever or button). This basic type of switch is called an SPST switch (single-pole, single-throw).
Of course, switches can get more complicated. Many of the switches that we will use, when activated, will break one circuit connection and simultaneously complete a new one. This type of switch is called an SPDT switch (single-pole, double-throw).
The switch we use most often is basically two SPDT switches bundled into a single switch and controlled by a single lever. This is called a DPDT switch (double-pole, double-throw). I will talk about this switch a bit more in the next chapter, as it is vital for mechanically reversing a motor direction.
One of the key components of bot building is motors. There are a number of different types of motors to choose from, but in this book we will be using a few different types of DC motors.
The main motor used in about 75% of the Simple bots I made is called a servo motor. A servo motor is basically a special type of DC motor with a gearbox. These work well because they are a standard size, have a bracket (called a horn) that you can mount things to, are controlled by low voltages and have a fair amount of torque. You can find servos in a number of different sizes, with different speed ratings, and different torque ratings.
All of the servos used to make Simple Bots have their controller boards removed.
Aside from servo motors, we will also be using reversible DC motors, computer fans, and vibrating motors (which are basically modified reversible DC motors).
Another commonly used motor, is the vibrating motor. The vibrating motor is basically just a DC motor with an off-centered shaft. You can learn all about vibrating motors in this instructable.
Now that you know all about electronics, the one last set of skills that you will need is how to solder and how to desolder. Basically, these skills involve joining and disconnecting wires using a soft metal with a low melting point (i.e. solder). You can learn how to solder (and desolder) at the aforementioned links.