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FIRST® Robotics Competition (FRC®)
FRC Control System Component Details
- 2015-2019: roboRIO Control System overview
- 2009-2014: cRIO Control System overview,
- 2004-2008: IFI Control System overview
- 2001-2003: IFI Control System overview
- 1997-1999: FIRST Control System overview
- 1995-1996: FIRST Control System overview
- 1993-1994: FIRST Control System overview
- 1992: FIRST Control System overview
General ReferencesCheck out:
How Electric Motors Work
Battery University for online practical battery knowledge
Battery Torque / Amp-Hour Calculator
Wire Gauge: Amps & Ohms - Find the gauge that's right for your job
How Gyroscopes Work
How Speed Controllers Work
Soldering Tips (pun intended)Extending Soldering Iron Tip Life
Wire LossesIn FRC we are limited to one 12v 17-18Ah battery. This battery has internal resistance (a good battery might be .015 ohms) which varies by age and condition, the wires used to transport our power also have resistance, as well as the electrical components like the main breaker, the power distribution panel, motor controllers, relays, etc. We lose voltage and power over smaller wire gauges and longer runs, so the power available to all our electrical components is less than that supplied by the battery at the source. 18 gauge wire loses 16 times what 6 AWG wire does, but of course 6 gauge wire is also 16 times heavier than an equal length of 18 AWG wire (weight for power).
Power loss (watts) = V * I
You can also think about how much voltage is lost for every foot of wire of various gauges. Assuming a motor is drawing 100 amps in a pushing match through 4 feet of #6 (.0004 ohms/ft battery to PDP & back) + 4 feet of #12 (.0016 ohms/ft PDP to motor & back):
Voltage loss = 100amps *(.0004*4) + 100amps * (.0016*4) = 0.8 volts lost to just the wire length
We can use this wire size table to get the resistance per foot of various wire gauges: Wikipedia-AWG wire sizes
LED Resistor CalculatorWhat resister do you need in series with your LED to get it to work correctly.
Remember though that some LEDs come with an integrated resistor, so be aware of what you are buying.
LED Resistor Calculator
FRC Circuit Breakers
Snap-Action 30/20a Breaker Spec.
Snap-Action 40a Breaker Spec.
FRC circuit breakers are meant to protect only the wiring from over-current. They are not intended to protect components like speed controllers from failing. That’s why each breaker requires a corresponding gauge wire.
We use self-resetting 40/30/20 amp breakers that open when too much current makes them too hot. Metal expands, breaks contact to cut off the current, metal cools, reconnects to restore the current flow. Once a breaker heats up and trips it stays pretty hot and trips much more easily from then on. These mount in the Power Distribution Panel and are self-resetting for individual circuit protection.
The main power breaker is also temperature based, but it will not reset once blown. The good news is that you really have to do something wrong, involving a full short circuit, to get these to trip in FRC. The reason is that the 120A breaker, at room temperature, is nominally good with a 200% load for anything from 10 to 40 seconds before tripping. At 125% load, it may run for between 1 and 9 minutes before tripping depending on manufacturing variations. De-rating when the breaker is already warmed up to 100F can be anywhere from -5% to +25% over rated current.
120amp Main Breaker Spec. (, 238 KB)
Red Anderson Connectors SB50The red Anderson connectors are rated at 50 amps for long duration (thousands of hours) and includes a fairly significant safety factor. We use them for 2 minute matches, so they can run over their 50 amp rating quite a bit without getting warm in our FRC application.
Other Anderson Connectors can be used on motor contyrollers, motors, and other electrical components to make them easily interchangeable.
Here's an interesting spec. sheet pdf from the manufacturer of the Anderson connectors.
Red 50a Assembly (, 64 KB)
More Info. and other connectors (, 118 KB)
Pulse Width Modulation (PWM)This a communication method where a steady stream of variable-length pulses are sent to a motor speed controller to signal how much power it should output.
PWM visual example
In this video example the oscilloscope shows a PWM signal. The lower line is the period of time when the signal is at 0v, and the upper line is the actual duration of the ~5v pulse. This example starts at neutral (1.5ms duration), then a joystick is moved forward and the control gradually changes to a shorter pulse (~.7ms here - Note that the min/max pulse length can differ depending on the device). The PWM then returns to neutral (1.5ms) followed by a joystick move that lengthens the pulse to a high of 2.3ms in this case. A normal range is more typically .5ms/1.5ms/2ms.
A different type of PWM is also the method used by motor speed controllers to pulse power output to a motor to vary it's speed. It doesn't actually vary the power output, it uses short pulses of full power mixed with no power to instead produce the average power desired. So over a very short period of time neutral is off, while half power is 12v half the time mixed with 0v for the other half, and finally full power is a constant 12v output.
PWM Cable ManufacturePWM cables can be purchased in pre-made standard lengths, e.g., AndyMark PWM Cables
Or to create your own made to length PWM cables you just need the supplies and the crimper available from, e.g., Hansen Hobbies
Alternatively, parts for Molex-style connectors are available at:
- 50-57-9002: 2-pin housing
- 50-57-9003: 3-pin housing
- 16-02-0102: female pins
- 16-02-0114: male pins
- 863-0288: 2-pin housing
- 863-0254: 3-pin housing
- 863-0369: female pins
- 863-0488: male pins
For powering items while on the robot cart far from an outlet, e.g., Laptop. Replace the alligator clips with an Anderson Connector to run it directly off a spare robot battery. It's handy for waiting on queue, especially at Championship. We use it for powering laptops in the stands, on long road trips, and other places too.
Search Lowe's for 'power inverter'
Alternate/replacement robot control systems
After regular season competition major elements of the control system (cRIO) must be removed for reuse the next year. Teams have the option of purchasing another cRIO or to keep the old robots running here are some possibilities for replacement control systems (not for competition!).
Run Jags & Victors Without a cRIO
We all need a quick & easy way to run speed controllers for motor and mechanism tests in prototyping and in early construction of the robot without the control system. All that's needed is a PWM generator. You can build your own or purchase ready-made RC servo controllers to do the job simply and easily.
To replace the alligator clips on your charger or power inverter, here are the same red connectors we use on our battery and robot.
Make Your Own PWM Cables and Driver Station ConnectorsWhere to get .1" header pin connectors & servo wire (, 132 KB)
PWM Signal GeneratorA simple hardware solution for driving motors at variable speeds without a FIRST Robot Control System. Makes for quick and easy bench tests, testing prototype and final motor assemblies by the mechanical sub-team, without having to wait for the programmers or electrical guys to show up. Free your mechanical guys to test stuff on their own while you are safely far away using a PWM 555 based generator.
PWM Signal Generator (, 276 KB)
555 Timer the circuit is based on
DC Motor TachometerTurn any DC motor into a tachometer, a sensor to measure the instantaneous speed of a rotating wheel or shaft.
DC Motor Tachometer (, 120 KB)
12v Competition Battery TesterContrary to what you might expect, not all Competition Kit batteries are created equal. We have received brand new batteries that did not perform well at all while older batteries were outstanding! When youíre in a match itís critical to be able to depend on your power source to perform up to advertised specs. You don't want to have your battery drop suddenly to a low voltage. Our testing station started out as a way to evaluate the condition of our older, prior year batteries to tell us if we should order new spares.
12v Battery Tester (, 384 KB)
Source Data (, 36.0 KB)
MK 12v BatteryHere are the technical specs for the 12v battery we use for competition power.
Valve-Regulated Lead-Acid (VRLA) Gelled Electrolyte (gel) and Absorbed Glass Mat (AGM) Batteries (, 1 MB)
Analog Multi-position SwitchWith only one of the many unused analog inputs on the Driver Station you can make a multi-position switch to send a large number of possible selections to your robot. We've used this in the past to select mutiple arm pre-set positions, e.g., stow, pickup, carry, cap, high-five.
Analog Multi-Position Switch (, 26 KB)
*** Legacy IFI Control System Hardware & Whitepapers ***
2008 Electrical Rules SummaryA two page summary sheet of the critical power distribution robot rules for 2008. Wire gauge, colors, circuit breaker requirements, proper Spike and Victor wiring, Victor calibration, and finally the pinout assignments for Team 358's RC.
2008 Electrical Rules Summary (, 484 KB)
Electrical workshop - December 2007An in-house workshop on the standard robot electrical system, followed by practical proper wire stripping/crimping/soldering was held one evening. The workshop covered basic theory, major components of the FIRST robotic electrical system, details on the FIRST Robot Controller and how it works with the spikes and speed controllers to command things to happen, FIRST rules and restrictions on our electrical system design, wire gauges, measurement instruments, such as volt meters and oscilloscopes, etc.
Here is the supporting handout outline the workshop followed: Electrical Workshop 12/06/07 (, 36 KB)
Substitute 12v Power SupplyWhen the old IFI RC is needed, itís often not so convenient to lug around a full-sized 12v battery and itís accompanying support circuitry just to test programs and algorithms. A miniature power supply, perfectly adequate for driving the RC for testing purposes is as simple as a 9v battery. Although simply holding the battery to the RC 12v terminals will work, it's kind of hard to balance in position. By placing that 9v battery in a project box and adding the proper connectors a rugged portable power supply is created. The same technique can be used to create a portable power supply for the O/I board.
Substitute RC Power Supply (, 190 KB)
Portable Driver Controls Power SupplyIsn't it tragic that the robot, which is so free to roam where it will, should be tethered (figuratively) to an Operator Interface that must be plugged into an outlet to operate. Well free the robot from the tyranny of the wall outlet by building yourself a simple portable battery pack. This can also be constructed from rechargable batteries.
Portable Operator Interface Power Supply (, 124 KB)
No longer used, but still kicking around most FRC shops are the old Exide 12v batteries.
Exide Battery Spec.
(, 510 KB)
Double-up JoysticksFIRST published this wiring diagram to take advantage of the normally unused analog inputs on each 2000-2008 OI joystick port to hook 2 joysticks to a single port.
How to Use 2 Joysticks on a single OI Port (, 118 KB)
Victor LegacyVictor 883 Installation Info. (, 28 KB)
Victor 883 Users Manual (, 32 KB)
Victor 883 FET (, 221 KB)
2003-2006 RadiosIFI Radio Modem Operators Manual (2003-2006) (, 225 KB)
2007-2008 RadiosIFI Robot Controller Radio Modem Operators Manual (2007-2008) (, 87 KB)
IFI Operator Interface Radio Modem Operators Manual (2007-2008) (, 87 KB)
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