FRC Control System¶

Control System Basics¶

• Battery supplies Power to the Robot
• The battery connects to a Main Breaker and then a Power Distribution (PD) device
• Every other component that receives power from the battery is connected to a PD circuit, either directly or indirectly.
• This covers almost everything on your robot. The only exceptions are for cameras or coprocessors (other computing devices in addition to the Systemcore) that come with built-in batteries or take small USB battery packs.
• Every port on the PD that you use must be protected by a Breaker or a Fuse. You will use breakers to protect most devices. The minimum gauge of wire that you are allowed to use in each port is determined by which breaker or fuse is connected to that port—larger breakers/fuses require larger wires.
• Each port on the PD may only connect to one pair of wires. Most of your use cases, like powering motors, will involve connecting only one device per port, so only one pair of power wires is necessary.
• However, some small devices, like the four encoders on a swerve drive, can easily be powered together by a single PD port. To power multiple devices from one PD port, you can connect a smaller power distribution device, like a REV Mini Power Module, or splice multiple wires together by soldering them or using a terminal block.
• This 5-port Wago-style connector is our preferred way to make a four-way splice. Soldering, especially with power wires 18 AWG or larger, is not recommended.

Control System Communications & Signal Basics¶

The previous section only covered how to power your control system. This section will cover communication with your control system devices.

• The robot radio allows the Driver Station to communicate with the robot, and connects onboard devices with the robot controller. The radio communicates with other devices on the robot through Ethernet cables. The radio has 4 Ethernet ports—1 for the Systemcore, 2 for other devices (such as cameras), and 1 to connect direction to the Driver Station or other computer.
  • Avoid using the Driver Station port for onboard devices. Instead, you can use a dedicated network switch to provide more ports than the radio alone provides.
  • If you need additional ports on the radio, you can connect one port to an Ethernet switch and your additional devices to that.
• The Systemcore can control motors via its PWM or CAN interfaces. Modern FRC motor controllers support both protocols, though CAN provides bidirectional communication, and more advanced control. The Systemcore supports 5 native CAN buses, as well as external CAN Busses such as the CTRE Canivore.
  • CAN Busses have a bandwidth limit that should not be exceeded. Consider splitting devices across multiple busses to keep individual bus utilization lower. Devices that are on separate busses will not be able to communicate with each other. Be sure to keep sensors on the same bus as the motors that utilize them, such as your swerve motors and encoders.
• The Systemcore has 4 USB ports. You can also create a CAN bus by connecting a CTRE CANivore to the Systemcore through one of its USB ports.
  • It is also useful to use a USB port for a flash drive to store robot data log files. After each match at a competition, you can unplug it to quickly view the logs on your computer without needing to keep the robot powered on.
• Many types of sensors, like CTRE’s CANcoder, communicate over CAN, so you can wire them into your CAN buses just like motors
• Some other sensors, like TTB’s Thrifty Absolute Magnetic Encoder, can connect directly to the motor controller of the relevant motor
• For any other sensors, or for cases where you do not want to connect a sensor to its motor controller, the Systemcore also contains 6 Smart I/O ports. While these ports can be used in multiple ways, the most common is to read the outputs of digital or analog sensors.
• These ports can also function as Pulse Width Modulation (PWM) outputs or digital outputs.
  • PWM is another way to command a motor controller, but it is far inferior to CAN because it does not allow the motor controller to communicate at all with any other devices. A Smart I/O port set to PWM output can only control one motor controller, compared to the dozen or more devices you can connect to a single CAN bus.
  • Digital outputs can be used to control pneumatic solenoids
• The Systemcore also contains an RSL port

CAN (Controller Area Network)¶

• CAN can be wired in two different ways:
  • Daisy-chained: this is the way that CAN is meant to be wired, and it is the most common way that FRC components are wired. CAN wires originate at the Systemcore in one of the CAN bus ports. The wires then go to each component in order, ending at the terminating resistor. One full loop, as mentioned previously, is called a CAN bus.
  • Star topology (not recommended): This is the method used to branch the CAN bus by each individual component. This is used by some teams because in a normal CAN bus, if one component loses a connection, they all do.
    • With a Star topology, each component has its own individual “CAN bus”. This is not recommended at all in modern FRC, as the introduction of SystemCore allows you to split up CAN buses much further than originally.
    • Additionally, a star topology presents many issues as it is NOT AT ALL how CAN is meant to be wired.
  • Always place the resistor at the end of each loop. This will be a 120 OHM resistor in a WAGO, or if terminating at a motor with a powerpole adapter board, the Weidmuller connectors may be used.

Terminating Resistors¶

There are many ways to terminate a CAN bus, but the most common ways are:

• Using a 120 OHM resistor in a WAGO
• Using the Weidmuller connectors on a motor with a powerpole adapter board
• Soldering a 120 OHM resistor
• Using a 120 OHM resistor in a Power Distribution Panel (PDP) or Power Distribution Hub (PDH)
• Using the SWYFT CANender

Specific Electrical Components¶

Motors¶

• Motors are the joints of the robot; they control every moving and rotating component on most modern robots. Thus, wiring them is very important. There are two types of motors, brushed and brushless.
• In FRC, all that really needs to be known is that brushed motors aren’t usually used anymore. However, these types of motor can be used in specific applications as well as being offered in the KOP. Outlines of both types will be provided below before the motors most commonly used in FRC are discussed.
  • Brushed: Brushed motors have 4 components: The stator, rotor, commutator, and brushes. In this diagram, the rotor can be thought of as the shaft and rotor coils. They are attached to the commutator. The way it works is this: The stator magnets are permanent, and when electrons are passed from the brushes to the commutator to the rotor coils, it produces a magnetic field opposing the one created by the stator magnets’ fields. However, the magnets would usually stop rotating when the fields are in alignment.
    • How does this get prevented? The commutator uses a specific pattern of metal to make it so that the field always opposes that of the stator magnets, therefore causing rotation. Brushed motors are most commonly used in cheaper appliances.
  • Brushless: Brushless motors are like brushed motors in many ways. They can have an internal or external rotor (the diagram has an internal rotor). What you may notice about the motor is that it has no brushes. How then does it create opposite polarities? This is through an electronic circuit that detects how much the motor rotates.
    • This makes for less contact throughout the system and a more precise transmission of power, which is why brushless motors are used throughout the world and especially in FRC.

Brushed motor on left, brushless motor on right

Common FRC Motors¶

WCP's Kraken¶

Krakens are arguably the most powerful motor in FRC. There are two types of Krakens- X60 and X44 (For 60 mm and 44 mm Outer Diameter, respectively). * These motors have built-in motor controllers, called TalonFX, which will be discussed in more detail later. They have two screws for cooling ports on the side that can be removed and covered with electrical tape. * For Kraken wiring, there are two ways to go about it, but for both, the CTRE Torque Wrench is a tool that makes the application much better and removes hesitancy due to fear of overtightening bolts.

• You can use the built-in ring terminals. The Kraken comes with them, and with the torque wrench, they’re easy to install. The wiring guide is on the WCP documentation. This may require extra splicing for longer wire runs, but overall, they are a fine solution.
• WCP Powerpole Adapter Boards. This replaces the ring terminals with common FRC connectors: Anderson Powerpole connectors and Molex SL connectors, which will be taught later. One extremely important thing to note is that the screws for these are NOT able to be used for ring terminals. That can severely damage the controller and also cause CAN bus issues. These allow for a continuous run and easy removal of wires, no matter what length wire run is necessary. The non-flipped X60’s also allow for termination using their top Weidmuller connectors as a hub for a 120 Ohm resistor. X60 Board, Flipped X60 Board, X44 Flipped Board

REV's NEOs¶

REV's NEO (NEO Vortex and NEO 2.0 best picks for price)

CIMs¶

• CIM Motors are the only brushed motors seen on this list. They are the motors FIRST uses on their fields and the motors that come with the kitbot. Similar to NEOs, they are controlled with External motor controllers.

Motor Controllers¶

These are the devices that control the motors and help direct power and signals to each mechanism.

Gyroscopes¶

These allow for the positional accuracy of your robot, as shown on logs. This is important for the autonomous period of your robot in the match, as well as automatic positioning.

Power Distribution¶

Power distribution boards are how power gets around the robot. They can range from complex circuits to simple copper blocks.

Fuses and Breakers¶

• Breakers and fuses are what gets stuck into the power distribution boards so that your precious and expensive electronics don’t break from a potential voltage overload. They are meant to break the electrical connection after too much electricity is supplied, and thereby saving electronics from undergoing that hit. Fuses are sacrificial and always a one time use while breakers are able to be reused in cases, though they can be popped and be rendered unusable.
• Some components will list what breaker should be used on their website but as a general rule of thumb:
• 10-12 AWG Wire = 40A Breaker
• 13-16 AWG Wire = 30A Breaker
• 16-18 AWG Wire = 20A Breaker
• 22 AWG Wire = 10A Breaker
• REV's Breakers are the best choice.

Main Breaker¶

• The main breaker is varied in form and is a crucial part of the robot. It’s basically your robot’s on/off switch. It is required to exist and be accessible on every robot.

RSL (Robot Signal Light)¶

• The RSL is crucial to safety on the robot. It turns on when the robot is powered on and blinks when the robot is enabled.
• Wiring the RSL is relatively simple: Make sure the black wire strand from your two strand wire, or ground is in the middle port labeled N, join the two outer ports with a small piece of red wire, and then in the terminal labeled Lb, place the red wire strand from your two strand wire. For easy replaceability, get the RSL Lever Lock Hub. In both cases, use a small flathead screwdriver for either all wiring or placing the hub in.

Systemcore¶

• WPILib Introduction
• Alpha Testing

Smaller Power Distribution¶

These are like the power distribution boards, but they are used for electronics that may need less voltage. They would be used when you don’t have enough spots on your main distribution board.

Cameras¶

These are for vision processing. They’re important in both autonomous and tele-operated periods of your robot.

Sensors¶

• CANRange: Sensor that uses proximity to automate. Can be used in intakes or passthroughs to automate movement or running of other components (motors, etc)
• Limit Switch: A switch that is typically wired to the Digital Input/Output (DIO) of the RoboRIO. Used to track the range of a mechanism. The sensor contains a physical material, such as a lever, that is typically over an input (like a button). From there, it can track when the button is pressed.
  • This can be used as a hard limit to mechanism movement such as for elevator or pivoting mechanisms.
• Mag Switch: Mag switches are sensors that detect the presence of a magnet. Typically used to track distance, this sensor is usually used to hard-stops on mechanism movements.
• CANandColor: Sensor that is used to track proximity and color. Can be used in games that have two game pieces of different colors (such as 2025 Reefscape™)
• Beam Breaks: Sensor that includes an emitter and receiver. When an object passes through the emitter, a signal is sent to the receiver and this can be used to track the movement of a gamepiece within the robot. Automation can be used in pivoting mechanisms for movement.
• Absolute Encoders: These allow for the rotational accuracy of shafts. This is important for swerve drive accuracy rotationally as well as other precise mechanisms.
• CTRE's CANcoder - Quality Pick
• TTB Magnetic Encoder - Price Pick

Robot Radio 2.0¶

• VividHosting’s Robot Radio 2.0 (no link yet) is what gets the signal from the driver station to relay information to the robot to make it do all the fun things robots do. Placement of this is especially important and should be done with care.
• The radio should be mounted against a metal tube or plate.
  • Heat can build up inside the radio. By mounting the radio against a metal surface, you can conduct heat away, allowing it to disperse.
• Do not block the visibility of the status LEDs.
• The radio should not be fully enclosed by a case or mounting solution.
  • This traps heat in the radio and can cause the radio to overheat.
• The radio should be easily removable, as it is programmed for each competition.
  • Zipties are a great way to mount your radios.