Education

Here is an awesome paper by Wesley Aptekar on the subject of PID: Intro To Control Theory Part 1: PID I could not have explained this as well as he did so I think ill leave it at that! Clearly the hard part is picking the kP kI and kD values for your PID loop. These values change from system to system and sometimes even robot to robot despite being identical copies. Here is an awesome interactive post by Wesley so you can hopefully get a feel of what is like to tune a PID loop: Intro To Control Theory Part 2: PID Tuning It’s important to understand the concepts of PID however we hardly ever use them by themselves on our robot, they just don’t give you enough control. Say we want to accurately control the motion of a system at all times. This is where Motion Profiles come into play. Heres Wesleys blog on the subject, you can ignore everything that says “state space” and just read it as “PID”, also the math gets kinda gnarly so just skip over that part: Intro to Control Theory Part 5: Feed Forward and Motion Profiling Fortunatly for us, there is a ton of code already out there that does all of this for you! Talon SRXs are particularly special because they have all these methods of control built right in! We just need to plug in the constants and tune the values. Even tho it‘s incredibly easy to implement PID, its important to understand the fundamentals so you can better understand how and why a system acts the way it does. So to sum it up, you should understand the concept of error and that we want to bring the error of a system to 0. A PID loop is a great way to achive this because it accounts for the momentum of a system (doesn’t assume you can instantly decelerate). However, we can take this one step further and implement a motion profile. This is essentially changing the set point of a PID loop to controll its motion more closely. There is a lot of math that goes into finding the right constants for things however we can normally just guess and check to find them pretty quick.

Although we use lots of different sizes of wire around the robot we like to keep things standardized. A common rule of thumb is that a wire is either 4, 12, 18, or 20 awg (gauge) wire. I'll go over all of these and where they are used. 4 AWG The largest wire on the robot. We always use Kolossus Fleks Kable from here from knukonceptz. This wire is used to connected the batteries to the PDP. When connecting terminals to this 4 awg wire you might not be able to get all the strands in. This is fine! SImply pull the strands aside, insert wire into terminal, then use flush cuts to trim the wire that is left out. The picture to the right is by no means perfect, but is very acceptable. I'm sure you guys can do better. All crimps should be made with this tool. Remember to always do the pull test to after you make a crimp. Above you can see all the 4 awg wire used on the robot. A 2.5in long piece of .5in heat shrink should be used to cover the battery terminals. A 2in long piece of .5in heat shrink covers any other terminal. Do not use heat shrink on any of the power pull (large red plugs) wires, this makes the wires harder to fit into the connectors. Always ensure that your terminals lay flat. In this example the end of the terminal had to be grinded down slightly in order to sit flush. 12 AWG This size of wire can be found on the talons and on motor wires. We always use Powerwerx Zip Cord Wire. Talons should be plugged directly into the PDP. When inserting talons into the PDP use this tool. The tool should be inserted all the way into the connector when you insert the wire. Here is a great video showing how to do this properly. Here is a picture of what it should look like when done. On the other side of the talons 45 Amp Anderson Powerpole connectors should be used. Here is a great video on how to crimp these. These Andersons are used give us modularity. They allow us to easily swap motors and mechanisms. 12 awg wire should never be soldered. 18 AWG This wire is used to connected various electrical devices together. We always use Powerwerx Zip Cord . In this examp le you can see the 18 awg wire being used to connect various components to the VRM. Note how the appropriate sized ferrules are used when the wire is plugged into a weidmuller connector (hole with white button). Here is a great video showing how to crimp these ferrules. The one exception to the 18 awg ferrule rule is when wiring the roborio. 18 awg stranded wire should be inserted directly into the roborio power connectors. 20 AWG This cable is also known as CAN Bus. We purchase our CAN cable from CTR-E. CAN bus is the signal cable on our robots. CAN allows all the components to be connected in a loop, avoiding the need to have each component have their own signal wire (NOTE BELOW: Some speed controllers use PWM which means they have to be individually plugged into the roborio, this is a pain!). You can notice the green and yellow cables in this diagram. It starts in the roborio, goes into all your CAN devices, and terminates in the PDP. All CAN wires should use these ferrules when inserted into weidmuller. When soldering 2 CAN wires together, don't be afraid to cut the wire as short as possible. Even the CAN wires on the Talons can be replaced relatively easily. Use proper solder techniques and always heat shrink your work. I would consider the CAN wires in this picture to be a little Short but Like I said don't be afraid to make them nice and tiny. All CAN wires should be twisted together along the entirety of the robot. Here is a picture of a nice completed CAN loop. Note how all the wires are ziptied flat to the belly pan. CAN wires are a huge failure point so it's important to take every precaution to ensure the loop is perfect.

In this section I hope to give a brief explanation of each of the electrical components. By the end, you should be able to correctly identify and understand the functionality of each of the devices. Lets begin. Roborio At the center of every robot is a brain. The roborio, produced by National Instruments, is what provides a large majority of the functionality to a robot. While it's not the only processor on board it, it does a majority of the computing. The roborio serves as a hub for sensors, signal wires, and other electronic devices and allows them to all communicate. If your into computers you can think of the roborio as the motherboard/processor. Power Distribution Panel (PDP) The PDP provides power to not only the various electrical components but also to the motors. The battery is directly plugged into the PDP and the PDP regulates and distributes this power safely around the robot. Talon SRX The Talon is a motor controller. It takes power from the PDP and gives fine motor control. The talons take their orders from the roborio. Because the output of the talon is connected to the motors (1 motor per talon) you can use this system to turn your motors on, off, or anywhere in between. The talons can also do some really fancy in regards to controlling your motors, but that can be saved for a programming lesson. Talons are preferably connected to the PDP in a "Butterfly" layout like shown above. This keeps wires short and things easy to maintain. A more advanced reasoning behind this is the concept of resistance. Longer wires create more resistance, so keeping everything as short as possible really improves your robot performance. Voltage Regulator Module (VRM) The VRM is a small device that is used to deliver electricity to various low power devices such as LEDS or sensors. Similarly to the PDP, the VRM distributes electricity all over the robot. Pneumatics Control Module (PCM) The Pneumatics Control module is used to control the various pneumatic components such as the compressor and solenoids. We will go over pneumatics in another lesson but for now you can just understand that the PCM is another small PDP, similar to the VRM. Radio The radio allows us to wirelessly control the robot. We connect to the robots wifi signal and control the roborio wirelessly. Wiring Layout This is a wiring diagram showing how all the components are wired together. We will go into a ton more detail about most of this stuff but this a good graphic to visualize everything.