Glossary

Many terms used in FTC and Game Manual 0 that are unfamiliar to teams may be found here. You’ll be able to quickly learn the lingo of FTC!

Anderson PowerPole

Anderson PowerPole is a connector used by AndyMark on their NeveRest motors. PowerPole connectors are very reliable and recommended for teams. In addition, there are adapters available to other systems.

Anderson powerpole connector
Ball Bearing

Ball bearings refer to bearings with steel balls arranged in a circular fashion. This allows rotation of an element with less friction than a bushing, primarily because the surface area (or contact area) is much less than in a bushing.

Bearings are definitely recommended for drivetrain and high speed usage. Bearings are used in the Actobotics, goBILDA, and REV kits, and are commonly sold by most robotics vendors.

Actobotics dual ball bearing hub

Actobotics dual ball bearing hub

Banebots Gearbox

The Banebots gearbox is a heavy-duty gearbox that can be attached to RS-555 series motors. It has high gearing options for teams to choose from if they wish to build a mechanism such as a rotating arm.

Banebots gearbox
Bare Motor

A motor that does not have a gearbox attached to it.

A bare NeveRest Classic Motor (am-3104)

A bare NeveRest Classic Motor (am-3104)

Bevel gear

Bevel gears are gears that transfer power along different axes, which are perpendicular to each other. Bevel gears are generally considered more inefficient than regular gears.

However, bevel gears can be very useful, especially in areas of limited space where the motor can be placed perpendicular to the element it is driving, and not in the same plane.

3736 Serious Business' use of bevel gears in Rover Ruckus

3736 Serious Business, Rover Ruckus

Bore

The bore refers to the shape of the opening that the shaft is inserted into. For example, the bore for a 5 mm hex shaft is the hexagonal shape.

“Stripping the bore” means that over time, the bore will lose its hexagonal shape, and become close to a circular shape, rendering the bore (and subsequently, the part it is on) useless.

A bearing with a hex bore
Box Tube

Box tube is aluminum shaped into hollow square or rectangular profiles. Commonly used in FRC, box tubing is seen less in FTC; however, small box tubing can be used for drivetrain or elevator purposes. Generally, we recommend new teams stick to kits unless they are prepared to tackle custom mechanisms.

A piece of box tube
Bushing

A bushing is primarily mounted on the outside of a shaft. It rotates in a pillow block, which holds the bushing. Generally, both are made out of a low-friction material such as Delrin or bronze.

Bushings are less efficient than ball bearings because they have a larger surface of contact, but are acceptable for low-load situations or low-budget teams.

A REV Robotics bushing

REV Bushing

A REV Robotics pillow block

REV Pillow Block

Cantilever

A cantilever refers to when an object (usually a shaft) is only supported on one side. While this provides theoretically less support, as long as the shaft is still supported at two points by bearings or bushings, cantilever is still a sound building technique. Many drivetrains are cantilevered, which provides for easy access to wheels.

Note

Supporting the shaft on both sides is theoretically more structurally sound, although in most cases you won’t notice a difference.

Sanford's cantilever 6WD prototype

Sanford’s Prototype

C2C

Center to center (C2C) refers to the distance between the centers of a pair of sprockets, pulleys or gears. This will affect chain/belt tension and gear meshing, so calculating this correctly is essential.

Center drop

Center drop refers to a 6+ wheel tank drivetrain with the center wheel (usually a traction wheel) mounted slightly lower than the other wheels, thus “dropping” that wheel. Dropped drivetrains have more turning agility than non-dropped tank drivetrains as wheel scrub is reduced.

Chain

Refer to sprocket for more information.

Chain Breaker

A chain breaker is a tool used to ‘’break” the chain by pushing out the pin in the chain link, and reconnects it by reversing the operation.

Note

We highly recommend purchasing the DarkSoul chain breaker if you plan to use chain.

Channel

Channel (more precisely called C-Channel) is aluminum that is in the profile of a C. (It is also sometimes called U-Channel.) Channel, along with extrusion, is the most common structural build element in FTC, and is found in Tetrix, REV, Actobotics, and goBILDA kits.

Channel is fixed pitch, which means that there are pre-drilled holes that limit mounting to finite locations. It can be used to easily construct drivetrains; however, be aware that gear and chain mesh may not be with channel.

A piece of tetrix channel
Churro

Churro is a 1/2” or 3/8” hex product sold by AndyMark. It has a bore that is easily tapped to accommodate 1/4-20 and 1/4-28 bolts, and is commonly used as a large standoff. It is light and cheap compared to other hex products.

Warning

Using churro as shaft is highly discouraged, as it is slightly undersized as well as prone to twisting.

A piece of churro
Clamp Mounting

Clamp mounting refers to securing a motor primarily by using friction instead of screws attached to the motor itself. This is generally discouraged as the motor can become loosened over time.

Tip

Use friction tape around the surface of the motor that is clamped down so that it will have less chance of moving around.

A TETRIX v1 motor attached with a TETRIX Clamp Mount

TETRIX clamp mount and v1 motor

Clamping Hub

A clamping hub is used to fixate part such as sprockets or gears on shafts. It is also used to prevent shafts from moving laterally. Clamping hubs are recommended over shaft collars because clamping hubs have more contact area than a set screw.

An Actobotics clamping hub
Colson Wheel

The Colson Performa Wheel, sold by VEX robotics and various sellers, is one of the premier traction wheels for FTC drivetrains. Offered in many different thicknesses and diameters, the Colson wheel can fit nearly any type of skid-steer drivetrain. The rubber on the Colsons provide great traction with impressive durability. It is sold in a 1/2” hex bore size, so teams will have to use Ultrahex or similar product in order to use Colsons.

A Colson Performa Wheel
Computer-aided design (CAD)

CAD is software most commonly used to aid the design and drafting of parts and assemblies in engineering. In FTC, CAD is used to make 3D models of robots as well as design custom parts.

COTS

COTS (Commercial Off the Shelf) parts refer to parts that teams can purchase physically or through an online retailer.

Warning

FTC teams are limited to one degree of freedom (with some exceptions) to COTS parts. Therefore, buying a drawer slide is an allowable part, as there is only one degree of freedom, but purchasing a multi-axis arm isn’t.

However, teams can buy individual parts and assemble them together into a mechanism that has more than one degree of freedom. This doesn’t apply to drivetrain kits.

Compliant Wheel

The compliant wheel, sold by Andymark, is a flexible rubber wheel that is primarily used for intakes.

Warning

These are not designed for use in a drivetrain.

The available bore options are 1/2” and 3/8” hex bores, as well as 8mm round with a TETRIX hole pattern (4 inch only). As with the compliant wheels, durometer (hardness of rubber) affects both traction and longevity, sacrificing one for the other. However, in the case of intakes, a lower durometer is recommended to have maximum grippiness for intaking game elements.

Note

Keep in mind that elements may get jammed at unfavorable angles in your robot.

An alternative to the compliant wheel is the West Coast Products Flex Wheel. These wheels, while less common, serve the same function as compliant wheels, but are generally considered more durable. However, for sizes greater than 2”, you will need to design and manufacture a custom hub in order to create a mounting point.

Recently, goBILDA released the 72mm Gecko Wheel, which integrates very well with the goBILDA ecosystem. However, at the time of writing, to our knowledge, these are untested by FTC teams.

A 2" green compliant wheel

A 2” compliant wheel

A 4" green compliant wheel

A 4” compliant wheel

Compound Gearing

Compound gearing refers to multiple reductions in order to transmit power from A to B. This is used when a specific reduction might be needed, or due to space issues. Compound gearing can be achieved by placing two gears or sprockets of different sizes on one shaft.

Core Hex Motor

The Core Hex Motor, sold by REV, is different from the standard RS-555 series motors that are generally used by FTC teams. It features a 90 degree orientation and does not contain an output shaft. Thus, teams will have to cut 5 mm hex shaft to length as needed. The Core Hex motor has a slow gear ratio (72:1), and is not as powerful as the RS-555 series motor.

Warning

We advise teams to go against the Basic Bot Guide provided by FIRST, as Core Hex Motors should NOT be used to power drivetrains.

A REV Robotics Core Hex motor
DarkSoul

The DarkSoul chain breaker, designed for motorsport application such as BMX, is compatible with the FTC standard #25 metal chain.

Analogs of this include the REV #25 chain breaker and the VexPro #25 chain breaker. REV and VexPro claim that they have made FIRST specific improvements to this chain breaker.

It is highly recommended that teams purchase this chain breaker if they are planning to use #25 chain.

A DarkSoul #25 chain breaker

A DarkSoul #25 Chain Breaker

Dead Axle

A dead axle refers to an axle that intentionally does not spin. Instead, bearings are mounted directly to the moving part, such as a wheel in a drivetrain.

Power is transferred with a sprocket, pulley or gear that is also directly mounted to the moving part. This eliminates the need for the axle to transfer torque, and also eliminates the need for hubs. Additionally, the axle can be used for structural integrity, as it is rigidly mounted.

Defense

Defense is a strategy employed with the goal of preventing the opposing alliance from scoring points, or at least significantly slowing the opposition’s scoring.

This strategy can backfire if drivers illegally play defense and incur penalties and/or cards for their alliance. Defense is usually played by obstructing the opposing alliance, either by strategically positioning the robot to obstruct access or pushing another team’s robot into a disadvantageous position.

Direct Drive

Direct drive refers to mounting a wheel directly on the shaft of the drivetrain motor. This means that there cannot be any change of gear ratios between the motor and wheel.

Warning

Direct drive is not recommended because shock loads transfer easily between wheel and gearbox, and can break the gearbox, especially in drivetrain use.

An example of direct drive found in REV's Basic Bot Guide

Basic Bot Guide - REV

Disconnect

A disconnect (DC) is when, for any reason, the robot is not able to be controlled from the gamepad. This can happen for many reasons - static buildup on the robot, a loose cable, or an error in code.

Generally, most DCs are caused by improper wiring, so wire stress relief is encouraged for all teams (USB Retention Mount). They can also be caused by WiFi disconnects, or an ESD (electrostatic discharge) shock to the electronics.

Driver Station

The Driver Station (DS) phone refers to the phone that is used by the drive team and connects to the gamepad(s).

Durometer

Durometer refers to the hardness of rubber. Having a high durometer translates to a harder rubber surface, more durability, but less traction. A low durometer means a softer rubber, worse durability, but improved traction.

Encoder

An encoder refers to a device that tracks (generally) rotational movement around an axis.

There are both absolute and relative encoders. An absolute encoder will report at exactly what angle the shaft is compared to its absolute “zero”. A relative encoder will report how far the shaft has rotated since it started tracking (for example, when autonomous starts).

Encoders are used to help find the position of where the robot, or one of its mechanisms, is.

Extrusion

Extrusion is aluminum shaped into slotted profiles able to accept certain types of hardware. For FTC, the most common is the 15mm extrusion, used in the REV and Misumi products. 15mm extrusion accepts M3 bolts and nuts (note that only regular M3 nuts can fit inside the slot, not locknuts).

Extrusion is not a fixed pitch system, allowing teams to adjust components as they wish. This makes it simple to achieve correct tension and put mechanisms where channel would limit mounting. The adjustability of extrusion is especially useful in precise situations, such as intake geometry.

A piece of REV Robotics extrusion
Face Mounting

Face mounting refers to mounting the motor by affixing the motor directly to the mount using bolts. This is the preferable way of mounting the motor (compared to clamp mounting) because it is less likely to loosen over time, especially with the use of Loctite on the bolts.

Note

It is advisable that 4-6 bolts be used to face mount for redundancy.

Additionally, there is no way that the motor might rotate and cause a loss of tension in belts or chain.

A REV Robotics v2 motor facemounted to a plate

REV v2 Motor Facemounted

Gauge

Wire gauge refers to the diameter of wire. AWG stands for American Wire Gauge, the general system used in the US. The larger the gauge number, the smaller the wire diameter. Generally, servo wires are 22 AWG and motor wires are 18 AWG.

Gear

A gear is a machine part that has cut teeth, usually written in the form “numberT” (e.g. 32T, 86T). Its purpose is to transfer power from the motor. Gears can be made in different materials. The most common is aluminum, while Delrin plastic may also be used.

A 56T REV aluminum gear

56T REV aluminum gear

Gearing Up

Going from a higher gear ratio to a lower gear ratio. (i.e. 20:1 → 10:1).

Gearing Down

Going from a lower gear ratio to a higher gear ratio. (i.e. 10:1 → 20:1).

Gearmotor

A component consisting of only one motor and one gearbox.

Gear Reduction

Also known as a gear ratio. In any rotational power transmission system (typically involving motors and servos in FTC), a gear ratio defines both the number of rotations of the system’s input and the number of rotations of the output.

For instance, a NeveRest 20 gearmotor consists of an unmodified NeveRest Motor and a planetary gearbox that has a gear ratio of 20:1 (or, when spoken, “20 to 1”). This means that in order for the output shaft of the gearbox to rotate 1 time, the input shaft of the motor must rotate 20 times. Gear ratios are one of the most important design considerations about a power transmission component.

Any FTC motor or servo has two properties: speed and torque (or rotational force). These two properties are inversely proportional, meaning that increasing speed decreases torque, and vice versa. For instance, if one wishes to make a mechanism faster at the expense of torque by doubling the speed of that 20:1 gearbox, they would decrease the gear ratio by a factor of 2. Since 20 divided by 2 is 10, the new desired ratio would be 10:1 (this is referred to as gearing up). However, if one wishes to double torque instead, making the system more powerful and robust at the expense of speed, they would increase the gear ratio by a factor of 2, leaving them with a 40:1 ratio (this is referred to as gearing down).

The most common ways of gearing up or down are using gearboxes, gears, sprockets and belt-driven pulleys, all of which exist in various sizes.

Grounding Strap

The REV Grounding Strap is used to ground the metal frame of the robot to the XT30 port of the Expansion Hub. It is currently the only legal way to ground your robot.

A REV Robotics grounding strap
HD Hex Motor

The HD Hex motor, sold by REV Robotics, is a RS-555 series motor with spur gear and planetary gearbox options. The motor has a 5mm hex output shaft compatible with REV’s motion system.

A REV Robotics HD Hex motor
High Strength Hex Hub

REV’s hex hub is a steel attachment whose purpose is to prevent the bore wearing out over time. The strengthener fits on the 5 mm hex shaft and into the gear, sprocket, or wheel.

Note

It is highly recommended that all teams who use 5mm hex use strengtheners on all driven wheels, gears, or sprockets to prolong their longevity and prevent bore stripping.

A REV Robotics High Strength Hex Hub
Holonomic drivetrain

Holonomic drivetrains utilize mecanum and omni wheels in order for the robot to strafe and turn. The most common holonomic drivetrain is a four wheel mecanum drive.

HTD Belt

HTD belt is a type of synchronous timing belt commonly used on drivetrains. It is available in different widths to accommodate different sized pulleys. The most common is 3mm and 5mm belt, which can be purchased from various online vendors.

A picture of various HTD belts
Idler

An idler gear, sprocket, or pulley is one that is purposely not used for driving anything else on the shaft. The purpose of this idler is, in the case of gears, to transfer power to another direction.

For chain and belt, idlers are more common, and are usually adjustable to maintain tension.

JST-PH

JST-PH is a type of connector. For FTC, the 3-pin and 4-pin options will be used most often. For the 3-pin connector, it is used for RS-485 connections.

JST-VH

JST-VH is a type of connector used by FTC motors to interface with the REV Expansion Hub. It is keyed and locks into place for improved reliability.

A cable with JST-VH connectors
Laser cutter

A laser cutter is a tool that uses a high-power laser to cut through sheet metal or similar material. The laser is guided by CNC to cut preprogrammed patterns into the sheet.

Lead Screw

A lead screw is very similar to a threaded rod. It is used for high load and high torque application such as hanging. However, due to the nature of the threaded rod, lead screws are generally quite slow compared to linear slides. The speed of a lead screw is determined by two factors. The first is how fast the motor outputs, and the second is the number of threads per inch (TPI).

A leadscrew
Linear Actuator

Linear actuators are basically servos that translate their output into linear motion, instead of rotational motion. Linear actuators are rarely used in FTC due to its prohibitive cost, but they may have some uses in special applications.

Locknut

A locknut is a nut that resists vibration by the nyloc inside. Nyloc is a type of plastic that holds the bolt securely on to the nut when it is screwed in. It is advised that teams purchase locknuts instead of regular nuts as FTC mechanisms often become loose over time.

Loctite

Loctite is thread locking fluid used so that bolts do not come loose under use and vibration. Loctite should be applied to the threads of the bolts. There are two types of Loctite: blue, which is removable, and red, which is permanent (and we mean it).

Note

It is highly recommended that teams use Loctite on all motor and servo mounts, as well as any mechanism prone to vibration.

Danger

THE BOTTLE COLOR AND THE FLUID COLOR ARE REVERSED. When we refer to the “color”, we mean the fluid color. Blue loctite usually comes in a red bottle.

A red bottle containing blue (removable) loctite, and a blue bottle containing red (permament) loctite

Blue Loctite (removable, in red tube), Red Loctite (permament, in blue tube)

The master link is a piece of metal that acts as the connector piece for chain. The link comprises one side of a chain link, and the other side is a special single-sided link piece which accommodates the master link. The master link may be removed easily to allow the chain to be shortened or lengthened.

However, because it is removable, it is not very reliable and can break off.

Mecanum Wheel

Mecanum wheels are a special type of wheel that enable maneuverability and holonomic strafing as opposed to traditional wheels. They consist of a series of rubber rollers rotated 45 degrees to either the left or right.

In a conventional mecanum drivetrain, running the wheels on one diagonal in the opposite direction to those on the other diagonal causes sideways movement. Combinations of these wheel motions allow for vehicle motion in any direction with any vehicle rotation (including no rotation at all).

A Nexus 100 mm mecanum wheel
Mesh

Meshing refers to the overlapping contact between a gear tooth and another gear tooth, chain and sprocket, or belt and pulley.

A proper mesh is essential to ensure maximum torque transmission. Too little mesh can result in no power transfer, derailment or gears grinding/wearing down faster. Too much mesh can produce unwanted friction and introduce inefficiencies within the drive system.

Micro USB On The Go (OTG) Cable

The Micro USB OTG cable connects the Driver Station phone with the Logitech controller that the driver uses in order to control the robot.

Note

It is recommended that teams purchase a couple spares due to faulty OTG cable connections and its low price.

A USB OTG Cable
NeveRest Motor

The NeveRest Motor, sold by AndyMark, is a RS-555 series motor that is available in spur gear and planetary options. It has a 6mm D-shaft output compatible with Actobotics motion system.

Odometry wheel

An odometry wheel is a small unpowered wheel (usually omni wheel) that tracks the distance the robot has traveled through the encoder attached to the wheel’s axle.

Usually, there will be two or three wheels - one or two on the x and y axis each to track the front-back and left-right position relative to the starting point. Generally, odometry wheels are sprung so that the wheel is in contact with the floor tiles at all times to ensure accuracy.

Omni Wheel

Omni(directional) wheels, sold by many different vendors, are a special type of wheel that prioritizes mobility and strafing (moving laterally) over traction or front-back movement. They are similar to mecanum wheels in that omni wheels have rubber rollers that rotate perpendicular to the plane of the wheel.

Thus, the robot can move sideways (although the robot is not powered in the sideways direction). It is also utilized as a low-friction wheel in 4 wheel, 6 wheel, and 8 wheel drivetrains instead of having corner traction wheels.

Furthermore, X-drive utilizes four omni wheels, though traction is at a minimum.

A mecanum wheel is technically an omnidirectional wheel, but when generally referred to, an “omni wheel” has rollers rotated 90 degrees to the rotation of the wheel, where a mecanum wheel is generally 45 degrees.

A REV Robotics omni wheel
Packaging

Packaging refers to the relative size and location of components on the robot. Generally, you want to design and locate (or package) components in the most space-efficient way you can.

Parallel Plate Drivetrain

A parallel plate drivetrain is a drivetrain that has drive pods that consist of 2 plates spread apart with wheels and drive transmission in between them.

These plates can be anywhere from 1” to 5” apart, depending on the space requirements of the wheels and drive system. Generally, a pod width of 3” or less is desired to maximize the space between the drive pods for mechanisms such as an intake.

Pitch

Pitch refers to the center-to-center distance between one tooth of a gear or sprocket to another.

Pitch Diameter

Pitch Diameter (PD) is the imaginary circle that mates with any other gear’s pitch diameter when the gears are properly spaced. The pitch diameter will always be smaller than the outside diameter of a gear.

Planetary Gear

Planetary gearing consists of a center gear (sun gear) which has smaller gears (planet gears) revolving around it. The outer radius has a ring gear which holds the other gears in place. Refer to Gearbox Internals for more information.

Pocketing

Pocketing refers to cutting out excess material from a CAD designed part. Pocketing helps to reduce weight and can increase strength of a part. This may seem counterintuitive (how can removing material strengthen a part?) but pocketing can reduce stress buildup, especially at corners.

Pocketing is often seen on drivetrain sheet metal plates which will be CNC machined. In FRC, pocketing is often used to reduce weight of the rectangular aluminum tubes.

731 Wannabee Strance 2019 VCC outer mechanism plate
Polyurethane tubing

Polyurethane tubing is a type of clear tubing that is stiffer than rubber or latex tubing. It is sold in different outer diameter sizes and thicknesses, and can be fitted inside of surgical tubing to make it stiffer.

A piece of polyurethane tubing
Punch Tubing

The REV Punch Tube is 15 mm aluminum tubing that allows teams to use the 15 mm REV building system without having the disadvantages of extrusion, such as that parts come loose over time.

With punch tubing, teams must pre-drill holes and attach, unlike extrusion, where teams can slide and adjust mechanisms.

Thus, it is recommended that teams use extrusion in prototyping/iterative design, and use punch tubing on the final iteration of their robot to save money. Punch tubing is compatible with the Metric Step Drill and 1/8” or 3.2mm pop-rivets.

A piece of REV Robotics 15mm punch tubing
Ring Gear

Refer to Gearbox Internals for more information.

Robot Controller

The Robot Controller (RC) phone refers to the phone that is on the robot and is connected to the Expansion Hub via the Micro USB cable. This can now be replaced by a Control Hub.

RS-550 Series Motor

The RS-555 series motor is the standard motor in FTC. It forms the base for the Andymark NeveRest, REV HD Hex, and goBILDA Yellow Jacket motors.

A RS-555 motor, in the form of a bare NeveRest motor
Servo

A servo is a small DC motor attached to servo gears that is very finely controllable. Servos are used in FTC for high-precision applications that are low-load - for example, opening a trapdoor for balls to fall through. The output has splines, which are the rigid teeth that are on top of the servo.

Commonly, FTC uses 24 and 25 tooth splines, meaning there are 24/25 teeth around the circumference of the output shaft.

There are many different types of servos legal for use in FTC - for information on how to choose the right servo, refer to Choosing a Servo.

A Hitec HSB-9370TH servo
Servoblocks

Servoblocks, sold by Servocity/Actobotics, are a way to mount servos to the Actobotics system. It is by far the best way to mount servos because it decreases the load on the servo spline, which is the weakest part of the servo. This is because under load, the servo spline teeth can easily become stripped, rendering the servo unusable. While Servoblocks are not cheap, they are one of the best investments for teams to pursue.

An Actobotics Servoblock
An example of a servoblock being used on a robot

10030 7 Sigma, Relic Recovery

Servo Power Module

A Servo Power Module (SPM) is a device made by REV Robotics that boosts the voltage that the Expansion Hub provides to a servo. The Expansion Hub’s output for servos is 5V at 6 amps, and the SPM boosts the voltage to 6V and up to 15amps.

This is important for servos under high load conditions such as the Savox servo, as well as the VEX 393 motor.

A REV Robotics Servo Power Module
Set Screw

A set screw is generally a hex socket screw that is used to fasten parts such as sprockets or gears to a shaft, or to fix a shaft in place so that it doesn’t move around. Due to the hex socket, allen keys must be used to tighten and loosen set screws.

Warning

Set screws are not recommended for drivetrain and high-load applications since there is very little surface area in contact with the shaft (only the tip of the screw). This makes the set screw likely to damage the shaft. Therefore, set screws can become loose very easily.

If set screws must be used, then it is imperative to use Loctite to reduce the chance of them shaking loose.

Note

Clamping hubs are much preferred to set screws, as clamping hubs apply pressure to the whole diameter of the shaft, as opposed to just one point.

A set screw
Shaft

A shaft is a piece of shaped metal used in power transmission. Shafts are the primary method to transfer power from motor to wheel. Generally, shafts are made out of steel, so do not use a bandsaw to cut a shaft. Rather, use a hacksaw, as hacksaw blades can cut through steel. There are different kinds of bores in FTC, which are listed below.

  • Round shaft

  • D-shaft: has a flat part for set screws, otherwise round

  • Hex shaft: six sided shaft

  • Rounded Hex shaft: hex shaft that’s been rounded so that it can run in round bearings

  • Keyed shaft: round shaft which has a keyway (a slot) through the shaft

  • Square shaft: commonly used in VEX products

Shaft Collar

A shaft collar, which has a set screw, is fitted on to a shaft in order to secure parts.

A shaft collar
Spacer

A spacer is used for keeping parts aligned with each other in separate shafts. Generally, spacers are used because there isn’t space for a clamping hub or shaft collar, as those take up more space. However, spacers are very low-profile and hug the shaft closely. Spacers can be purchased in different configurations, from 1 mm to 15 mm. Custom spacers can also easily be 3D printed.

A 1.5 mm thick spacer

A 1.5 mm thick spacer

A 15 mm thick spacer

A 15 mm thick spacer

Sprocket

A sprocket is a mechanical part that transfers power through its cogs, which fit into chain. It is similar to a gear, except that instead of meshing with another gear, the sprocket meshes with chain.

The cogs have the same system as gear teeth, using “numberT” (e.g. 32T or 86T). Chain is sold in both metal and plastic varieties.

#25 roller chain is usually metal, while 8mm chain used in FTC is usually plastic but can be metal. Plastic #25 chain is not recommended for higher load applications, such as a drivetrain.

A REV Robotics Delrin 20 Tooth #25 sprocket

Delrin 20 Tooth #25 sprocket

Spur gearbox

A spur gearbox has spur gears which are stacked on top of each other. Gear reduction is achieved through different size gears on the same plane.

SRS Programmer

The REV SRS Programmer is a device that will send a special data signal to the REV Smart Robot Servos to control their electronic endstops, as well as the continuous rotation mode of the servo. It can also be used as a servo tester for other servos.

Standoff

A standoff is a fastener with two threaded ends and usually has a hex profile to be used with a wrench. These ends are usually female threaded, meaning that they can have a screw threaded into them.

This is usually a more compact alternative to a long screw and spacers, and can be used to space things out as well as fasten them. Custom standoffs can be made out of hex stock, such as AndyMark Churro.

Standoffs are usually used in drivetrain purposes, such as in parallel plate drivetrains, where the plates must be separated and supported by standoffs at equal distances.

A couple of standoffr
STEP file

A STEP file is a filetype used to store 3D data about a part. It is recognized by different CAD softwares including SolidWorks, Inventor, Creo, etc.

Stealth Wheel

The stealth wheel, sold by Andymark, is a typical traction wheel used by many FTC teams from new to experienced. Andymark sells the 2” diameter and 4” diameter, but most teams use the 4” diameter option for drivetrains.

It is available in different durometers (hardness of rubber) so that teams may select the option that best suits them. A lower durometer (such as 35A) means more traction at the cost of longevity. For this reason, a medium durometer such as 50A (blue) or 60A (black) is recommended. Generally, 50A wheels can survive a year’s worth of driving and use, but it is recommended to swap them out mid-season unless they are cleaned regularly.

Stealth wheels are available in different bore sizes, such as 1/2” hex, 3/8” hex, 8 mm round, and 5 mm hex. With the 5mm hex option, it is highly recommended to use the hex hub strengthener from REV in order to prevent the bore from stripping out.

A blue 4 inch stealth wheel

4” Stealth Wheel

Strafing

Strafing is the act of moving sideways or laterally (somewhat similar to drifting). It is possible with omni or mecanum wheels, and not possible with traction wheels.

Surgical Tubing

Surgical tubing is generally latex or rubber tubing. Its most common use case is in active intakes, and has been popular among teams for many seasons. Surgical tubing has a hollow center and is sold in different diameters and wall thicknesses. Teams can experiment with different kinds of surgical tubing, as well as adding polyurethane tubing in order to make the tubing more stiff.

A roll of surgical tubing
Tank drivetrain

A tank drivetrain has wheels set up in a parallel line. It commonly uses 4 or 6 wheels, but the most widespread tank drivetrain is a 6 wheel drop center tank drive. Tank drivetrains turn by rotating the left or right sides in opposite directions, or in the same direction at different speeds.

Thunderhex

Thunderhex is aluminum rounded hex shaft that comes in 3/8” and 1/2” hex sold by VEX Robotics. It has a center bore that can be tapped.

Its most notable feature is rounded corners, which allow it to fit inside 10.25 or 13.75mm bearings, respectively. Because of the nonstandard diameter, the cost advantage is negligible, but ease of assembly and better performance are its strong points.

A piece of thunderhex shaft
TileRunner

The TileRunner is an unassembled chassis kit sold by Andymark. Although a bit pricey, it is an adaptable plate drivetrain that teams can use year to year. Teams can fine tune ratios within the included gearboxes and swap out between traction, omni or even mecanum wheels.

A tilerunner drivetrain
Torsional Rigidity

Torsional rigidity refers to how difficult it is to twist an object due to an applied torque. This mainly refers to extrusion, as it is easier to twist extrusion than channel or an angle piece, for example.

Torsional rigidity has consequences particularly in building drivetrains, as the drivetrain is the last mechanism on your robot that should flex or bend when weight or force is applied to it.

Traction wheel

A traction or grip wheel is a wheel designed for maximum grip. It has an outer ring made of rubber, and its wide track ensures a larger contact patch with the ground. Traction wheels are commonly found in tank drivetrains. They are sold in different sizes and thicknesses by different manufacturers.

UltraHex

UltraHex is 1/2” aluminum hex shafting sold by REV Robotics. There is an inner 5 mm hex bore in the middle, which allows compatibility with REV’s 5 mm hex shaft motion system. The 5mm hex bore also allows for a 1/4-20 or M6 screw to be tapped into it. 1/2” hex is also compatible with many FRC vendors.

A piece of ultrahex shaft
USB Retention Mount

The USB Retention Mount, sold by REV, is a plastic part affixed to the Expansion Hub that relieves stress on the USB Mini port. This is especially important because if the USB cable is loose or disconnected, the robot phone cannot communicate with the Expansion Hub, causing a disconnect.

Note

For teams using an expansion hub, it is highly recommended for teams to purchase the USB retention mount.

A USB retention mount attached to a REV Expansion Hub
VersaPlanetary gearbox

The VersaPlanetary gearbox is a customizable gearbox attachable to RS-555 series motors. It is a high-end gearbox option for teams looking to construct mechanisms that require a high gear ratio, such as for arms.

A VersaPlanetary gearbox
VEX Motor Controller 29

The VEX Motor Controller 29 (MC29) is used specifically to convert the PWM signal used in three-wire servo cables to the two-wire cable that connects to the 393 motor.

It is highly recommended to protect the motor controller from any sort of impact, as they can easily break and/or have wires become detached. Also, it is important to have the MC29 as close to the Servo Power Module as possible, so that the signal doesn’t become overly noisy.

A VEX Motor Controller 29
VEX 393 EDR

The VEX 393 motor is a special type of motor that utilizes 1/8” square shaft. Therefore teams will have to fashion a custom motor mount and shaft adapter for the VEX 393.

Under FTC rules, it is classified as a servo. However, in order to use the 393, teams must purchase an adapter from the 2-wire motor cable to the 3-wire servo cable, called the VEX Motor Controller 29.

These items are not usually in stock during the season, due to the demand from both VEX and FTC teams. Additionally, teams must purchase a Servo Power Module from REV Robotics to boost the output that the expansion hub provides. It is advised that only experienced teams use the 393 motor for this reason.

A VEX 393 motor

A VEX 393 motor

A VEX 393 motor used on an intake

3736 Serious Business’ intake

V-Groove Bearing

A V-groove bearing is a special type of bearing which has slanted “grooves” that allow for extrusion or rails to slide in between the bearing. V-groove bearings are often used in FRC for constructing linear elevators.

In general, v-groove bearings are somewhat unnecessary in FTC unless a hang is involved, as the linear slide options presented in the Linear Motion Guide guide are more than adequate for most use cases.

REV Robotics V-groove bearings riding on 1" extrusion

REV Robotics V-Groove Bearing riding on 1” extrusion

Waterjet cutter

A waterjet cutter is a tool which cuts sheet metal and other materials via extremely high pressure water focused into a small stream. Waterjet cutters are commonly used in industrial fabrication and can follow preprogrammed instructions to cut patterns, similar to a CNC system.

West Coast Drivetrain

West Coast Drivetrain (WCD), is a type of 6 wheel drive drivetrain that was first pioneered in FRC by west coast teams like FRC 254 The Cheesy Poofs, giving it this nickname.

This drivetrain was later adapted to FTC use due to its simplicity, durability, and great handling characteristics. The strict technical definition of a West Coast Drive is a drop center 6 wheel cantilevered drive where the center wheel is powered by a dual or triple motor input and the other wheels are chained/belted to the center wheel.

Of course in FTC, this definition becomes much more lax, with most drop center 6 wheel drives being parallel plate.

Weight distribution

Weight distribution generally refers to how the weight of the robot is proportioned. It is desirable to have a relatively 50-50 (50% of weight in the front half, 50% in back half) so that the drivetrain has optimal manuverability and turning.

Wheel scrub

Wheel scrub refers to friction between the side of the wheel and the floor tile. It inhibits turning as the drivetrain must overcome this frictional force in order to turn the robot. Wheel scrub is most common on 4 or 6 wheel tank drivetrains that do not have a center drop.

XT30

The XT30 connector is used in the REV ecosystem through the Expansion or Control Hub. The XT30 through the REV Slim Battery provides power to the Expansion Hub, and teams will need an XT30 cable to transfer power from the main hub to a secondary hub. This is also the connector used on the REV Grounding Strap.

A XT30 male and female connector
Yellow Jacket Motor

Yellow Jacket motors are the RS-555 series motor and planetary gearbox sold by goBILDA. It has a 6mm D-shaft and is available in many different gear ratios from 3.7:1 up to 188:1.

A Yellow Jacket motor