A GUIDE TO FRC Hardware

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SHAFTS

• transmit rotational power along an axis
• FRC standardized sizes are in 1/2" and 3/8" diameters (measured from flat to flat)
• Types
• Hex Shaft: outer-hexagonal profile with sharp corners
• Thunderhex: slightly rounded 1/2" hex shaft with a small round pilot hole bored through it
• Churros: hex shafts with small concave dimples acting as weight savings
• Good for standoffs, supports, and low load shafts
• MAXSpline Shaft
• reliable and robust torque transfer (rotational force) allowing accurate and repeatable movements
• Relatively lightweight (made of aluminium)
• Interfaces with other REV components (wheels, gears, sprockets, and bearing blocks)
• Reduced Backlash: design of the shaft minimizes clearance between mating parts and improves overall rigidity of the system

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BEARINGS

• Ball Bearings
• facilitate independent rotational movement by supporting rotating shafts with minimal frictional loss
• ubiquitously used in all mechanisms at the ends of shafts
• for FRC, the OD (Outer Diameter) of a bearing will always be 1.125”
• Bushings
• have no roller elements and are usually plastic or bronze
• most useful for low speed applications
• have more friction than ball bearings but can handle higher loads
• lighter and cheaper than ball bearings

Bushing

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EXTRUSIONS

• Patterned: fixed pattern of mounting holes for mounting structures, gears, sprockets, bearings, shafts, motors, etc
• MAX Pattern
• Grid Pattern
• No Pattern
• T-Slot
• slots allow for brackets to be placed anywhere
• adjust design with ease, good for prototyping
• good for linear motion
• Require accompanying framing fasteners
• Plain Stock
• Come in different profiles including square/rectangular tubing, and c-channels (or u-channels)
• Best for customization, but requires precise machining
• Brackets: designed to secure pieces of structure together at varying angles

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Supports

⅜” Dead Axle Tube

#10-32 Tube Nuts

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Making Strong Connections

• Gussets: used to reinforce and connect structures at a joint on the same plane
• distribute load and prevent excessive stress at connection point
• Brackets: attach structural elements usually positioned at right angles
• Tube Plugs: pre-tapped endcap with holes on each face to easily join extrusions w/o exterior brackets
• Nut strips: continuous blocks of threaded holes on each face that provide mounting and support options

Gussets

Brackets

Tube Plugs

Nut Strips

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TYPES OF COMMON FRC WHEELS

• Mecanum: type of omni-directional wheel
• allows movement in any direction w/o turning the entire vehicle
• Rollers exert forces on objects in 2 different directions at once
• Expensive and heavy
• mecanum wheels on a drivetrain sacrifice traction and controllability
• can be viable for intakes by centering game pieces
• Omni: also omni-directional via arrangement of different rollers
• Allow game pieces to move freely in direction of rollers axis
• Rollers only spin in one direction at a time
• High maneuverability but no traction
• Good for intaking game pieces from different angles but does NOT always center game piece (used in conjunction with mecanum wheels)
• Compliant/Flex Wheels: flexible wheels used often for manipulating rigid objects
• great for intakes or internal conveyors
• will deform under high stress = NOT shooter wheels
• Relatively cheap
• Traction Levels: 30A, 40 A, 60A

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TYPES OF COMMON FRC WHEELS

• Star Wheels
• Compliant material allows rigid objects to be manipulated easily
• ignores variations in the objects being driven
• Multiple spokes allow the star to act as a brush = larger surface area interacting with game piece
• HiGrip (can also apply to Versawheels and Pneumatic wheels)
• included in FRC kitbots
• Innate rubber tread for grip and cushioning = tread doesn’t need to be replaced
• Wheels have to be entirely replaced when they wear out
• High traction and durability
• Treaded Wheels = aluminum hub + tread
• tread riveted or bolted onto the wheel for traction and is replaced after use
• Replace tread as it is used NOT entire wheel
• More consistent odometry

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FLYWHEELS

• Types of Flywheels
• Solid Roller Wheels
• Colson Wheels
• Stealth wheels
• Fairlane Wheels (not an official FRC wheel)
• all flywheels will be durable and high-traction = consistent grip without deforming at high RPM
• differences between wheels are the type of rubber used and their interaction with game pieces

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Power Transmission

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Motors

• convert electrical power into rotational mechanical energy
• Types
• Brushed DC Motors: internally commutated motors that run on DC using internal brushes that transfer electrical energy from a battery into rotating coils through a mechanical commutator
• Are less efficient and prone to wear due to contact b/w the brushes and rotor coils
• Brushless Motors: externally commutated motors that are more efficient and require less maintenance
• motors are selected based on their RPM/torque output and mounting placement

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PLANETARY GEARBOXES

• COTS gearbox using planetary configuration with preset gear ratios
• Prototyping Customizability: configuration of different stages result in different ratios, swap different motors, changes in output shafts
• VersaPlanetary: modular planetary gearbox designed for customizing speed/torque output with preconstructed gear ratios
• Stacked Stages: input stage, reduction stage(s), and an output stage
• Most versatile but inconvenient due to use of different plates to mount different motors
• Sold by vex
• MAXPlanetary
• most used planetary gearbox
• Relatively heavy and expensive
• Strong and easier to mount
• UltraPlanetary
• Relatively small
• Specialized with Neo 550 Motors

VersaPlanetary

MAXPlanetary

UltraPlanetary

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MOTORS

• electrical component providing rotational power for all mechanisms on the robot
• Types of Common FRC Motors
• Kraken X60
• Continuous high power usage (drive train, flywheels, mechanisms constantly running)
• Easy wiring
• Easy to program
• Kraken X40: identical power usage to the X60 but less thermal mass (can’t regulate heat as well -> overheats easily)
• Neo
• alternative to Krakens
• versatile
• Good for prototyping
• Neo 550: use when lacking space or weight for regular Neos
• Neo Vortex
• Through-hex-bore design = interchangeable shafts and integration with different robot mechanisms (prototyping galore)
• Also convenient for programming
• CIMS
• Only brush motor on this list
• Often apart of kit bots
• Useful to be familiar with when helping rookie teams

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SPROCKET & CHAIN

• Sprocket: sturdy wheels with teeth that lock onto a chain to transmit power
• as the sprocket spins, the teeth grab onto the chain to facilitate rotational movement
• Chain: method of rotational power transmission through a series of interconnected metal links
• Common Sizes: #25 and #35 chain with 0.25" and 0.375" pitch
• even # of links = stronger
• Chain tensioner: ensure constant tension even through long term use
• Sprocket-Chain System
• Often used to lift, rotate entire mechanisms
• High-durability, load capacity and torque
• Minimal slippage if properly tensioned
• Heavier and requires lubrication
• Difficult to work with & replace
• Calculations
• Tooth Count
• Pitch: distance between the centers of two adjacent teeth
• Clearance Diameter: diameter of sprocket with chain wrapped around it (pitch diameter + pitch)
• Outside Diameter
• Pitch Diameter
• Link Count
• Center-to-Center Distance

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PULLEY & BELT

• Pulley: wheel with a grooved rim or flange and flat, shallow teeth that interlock with belts
• Belt: method of rotational power transmission through a rubber strip w/notched teeth
• Pulley-Belt System (often used on intakes and end effectors
• Lighter and quieter
• Requires less maintenance and doesn’t require active tensioning (easy to work with & replace)
• Less durable and wears out over time
• susceptible to slippage
• Lower load capacity and torque
• Often used on the “interior” of mechanisms to transfer a game piece
• Calculations
• Tooth Count
• Pitch (typically 5mm)
• Pitch Diameter
• Belt Width (9mm or 15mm)
• Center-to-Center Distance

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Fasteners

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Main Types of Fasteners

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FRC Bolts

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Types of Nuts

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How Fasteners are Notated

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Common FRC Fastener Sizes

• Fasteners can be specified by their size #, diameter, threads per inch, and thread length
• Up to size #14, bolts are notated by: “size # - threads per inch”
• Size #14 and above, bolts are notated by: “outside diameter - threads per inch”
• Most Common Sizes
• 10 - 32
• ¼ - 20
• Thread length is notated via “10-32 x 2”

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Bolt Retention

• Loctite: thread locker that helps prevent bolts from coming loose from vibrations.
• Blue 242 Loctite: medium-strength, removable threadlocker
• Red 262 Loctite: permanent threadlocker needing heat for removal
• Green Loctite 648: used to retain bearings in holes or other retain cylindrical assemblies on shafts
• When to NOT use Loctite: polycarbonate and nylocks (plastics = bad)
• Nylon Lock Nuts (Nylocks): lock nuts w/ nylon rim preventing bolt threads loosening from vibrations

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Blind Rivets

• used for attaching relatively thin sheet metal parts without weakening the material
• Vibration resistant
• semi-permanent fasteners that only require access to one side of an assembly
• rivets are removed by being drilled out and replaced
• rivets are used for connections intended to be permanent
• rivet length should be selected based on the total thickness of the parts being joined to ensure strong connection
• Commonly used for mounting the bellypan

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Miscellaneous

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Miscellaneous

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Resources + More Info

• Common FRC Vendors
• https://wcproducts.com/ - West Coast Products
• https://www.revrobotics.com/ - Rev Robotics
• https://www.andymark.com/ - AndyMark
• https://www.thethriftybot.com/ - The Thrifty Bot
• https://boltdepot.com/Fastener-Information/Printable-Tools
• https://www.mcmaster.com/
• https://www.boltscience.com/pages/basics2.htm

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