Exploration of the

FRC Kit Drivetrain

Purpose

• We designed these slides to introduce the FRC kit drivetrain for anyone new to FRC.
• Our goal is to answer three questions.
• “What is the kit drivetrain?”
• “What does it do?”
• “How does it do it?”
• We chose our words carefully to keep these slides simple.

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Kit Drivetrain = “AM14U4” from AndyMark

• AndyMark is an online store for FRC robot parts.
• FRC provides the kit drivetrain as an option for all teams.

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*CAD models and multiple part images in these slides are from AndyMark.com

Build Instructions

• When building this drivetrain read and follow the AndyMark directions.
• They are really good!
• Video and Manual

What does the kit drivetrain do?

• The kit drivetrain allows teams to assemble the base of their robot.
• With the control system added, the robot can drive around the floor.
• The robot can drive forward, backward, and turn left and right.
• The drivetrain has two groups of three wheels.

Left group

Right group

Front

Rear

How does the drivetrain turn?

• When the groups of wheels spin in opposite directions, the robot rotates.

Left Group Forward

Right Group Reverse

Left Group Reverse

Right Group Forward

Frame

• The frame is the main structure of the kit drivetrain.
• The frame is made from bent aluminum sheet metal.
• They make the parts by cutting the designs from flat sheets of metal and folding them.
• The folds make the pieces harder to flex and twist.
• 6 parts, 2 of each
• Outer Rail
• Inner Rail
• End Plate

Frame

• Some of the holes are used for assembling the drivetrain.
• Some of the holes can be used for attaching items to the drivetrain.
• Some of the holes are for other drivetrain options that we won’t be using.

Frame

• For the long configuration, you must cut end plates shorter.
• The basic method for cutting metal is with a hacksaw.
• The part should be clamped or put in a vise to prevent it from moving while cutting
• When sawing, wear safety glasses and ensure no one else’s hands are near the part you are cutting.
• A miter box may be used to make a straighter cut.

Fasteners

• Fasteners are the parts of the robot that physically hold other parts together
• Nuts and bolts that hold the rails to the end plate are some of the fasteners used.

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Fasteners

• The bolt has spirals known as threads and a larger head; you may also know it as a screw.
• It has a hex shape inside the head that is used with a hex key to tighten the bolt into the nut
• The nut is short with spiral threads on the inside.
• Hold the nut on its outside hex surface with a wrench.
• This nut is a lock nut; it must be mounted with the plastic part away from the bolt head.
• Nuts and bolts have their threads twisted together to secure them in place.

Standoffs

• Standoffs make it harder to bend or twist the frame.
• The kit drivetrain use standoffs made from rods called “Churros” due to their churro like shape.
• Each of the tubes crossing between the rails is a standoff.
• Standoffs have bolts screwed into each end of them to secure them to the frame.

Motors & Gearbox

• The AM14U4 uses 2 motors and 1 gearbox on each side of the drivetrain to power the wheels.
• Electric motors spin when connected to electricity
• The gearbox converts the motors fast speed to a useable speed for the wheels.

Motor

Gearbox

Shafts and Axles

• Spinning parts are mounted on rods known as shafts or axles.
• They come in a variety of shapes and lengths.

Motors

• This motor is called a “CIM,” it’s pronounced ‘sim.’
• When electricity is sent to the motor’s wires, the output shaft spins quickly.
• This motor’s face has two mounting holes for bolts to attach the motor.’
• There are 2 other holes used for holding the motor together makes sure to use �the empty holes.

Output Shaft

Wires

Motor Can

Mounting hole

Motor Face

Gearbox

• The gearbox uses gears to reduce the speed of the wheels powered by the motors.
• If the wheels were connected directly to the motors, the wheels would spin very fast, but the robot wouldn’t be able to drive around, turn, push things, etc.
• This gearbox is named “toughbox mini.”

Gearbox Housing

• The housing for the kit drivetrain gearbox is made of plastic.
• It has many internal holes and cutouts to precisely place components.
• The housing matches up to cutouts on the inner frame rail to make the complete gearbox enclosure.
• The gearbox has 4 holes to allow it to be bolted to the inside rail of the frame.
• The gearbox housing also has holes for mounting the motors

Gears

• Gears are toothed wheels that allow motion to be transferred from one shaft to another.
• Two gears with properly interlocking teeth are called “meshed.”
• When a smaller gear turns a larger gear. The larger gear turns slower than the smaller gear.
• A set of two gears that change rotational speed is known as a “gear stage.”

Faster

Slower

Multiple Gear Stages

• When you need to reduce speed, even more, multiple gear stages can be connected together.
• This gearbox has two stages.
• The blue stage is 1st stage reduction.
• The pink stage is 2nd stage reduction.
• Gear speeds in this gearbox
• The green gears are spinning the fastest.
• The yellow gears are spinning slower and at the same speed since they are both on the same shaft.
• The red gear spins the slowest.

Fastest

Slowest

Medium

1st stage

2nd stage

Motor Output & Pinion

• Output Shaft - spun by the motor
• Spacers - stop the gear from touching the motor face
• Key - forces the gear to spin at the same time as the output shaft
• Pinion Gear - A gear mounted on a motor output shaft
• Retaining Ring - Keeps everything on the shaft from falling off

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Key (AKA machine key)

• In this picture, we’ve made the pinion gear transparent and hid other parts to highlight the key.
• The key fits into slots in both the shaft and the gear.
• Without the key, if you held the gear still, the motor shaft could spin inside it.
• With the key, the motor shaft and pinion gear have to rotate at the same speed.

Hex shafts and hex holes

• Hex shafts are a different way to ensure that objects on a shaft rotate with it.
• Instead of being round, hex shafts are a hexagon shape.
• When a gear, wheel, or another object with a hexagon-shaped hole of the same size is put on the shaft, the shaft and the object have to rotate at the same speed.

Bearings

• Bearings allow shafts to spin smoothly. They reduce friction.
• Instead of having a shaft rub against the side of a hole, bearings have balls inside of them that roll.
• The balls roll inside of tracks called “races,” the inner race spins with the shaft, and the outer race is stationary.

Bearing Flanges

• The bearing flange is a raised lip on the outside of somes bearings.
• The flange ensures that a bearing can’t go all the way into a hole.
• Which side of a plate the flange of a bearing is on is very important during assembly.
• For the kit drivetrain all the flanges are inserted from the inside of the robot.

Bearings

• The kit drivetrain uses various types of bearings.
• Bearings can have different outside sizes called their outer diameter or OD.
• Bearings can have different inside sizes called their inner diameter or ID.
• Bearings like shafts can also be round or hex for their inner opening.
• The gold rings on the bearings are called shields. They protect the balls from dirt.

3/8” ID round bearing

3/8” ID round bearing with flange

1/2” hex ID bearing with flange

Shaft ends

• The ends of shafts are often modified to allow them to be inserted into bearings.
• The kit drivetrain includes hex shafts with their ends rounded so they can be inserted into round bearings.

E-Clip

• The output shaft of the gearbox includes an e-clip to stop the gear from moving along the shaft.
• The e-clip snaps into a specially made groove on the shaft.

Hex Shaft and Hex Bearing

• The output shaft of the gearbox is a 1/2” hex shaft.
• The drivetrain includes hex bearings on the inner and outer rails to hold the hex shaft.

Wheel

• The kit drivetrain uses “AndyMark HiGrip” wheels, designed specifically for FRC robots.
• Each wheel has a circular hole pattern allows other parts to bolt to it
• The wheels have a rubber tread designed to not slip on the carpet.
• The kit drivetrain has 6 wheels
• 3 on each side
• 2 center wheel assemblies
• 4 corner wheel assemblies

Center Wheel Assembly

• The center wheel assemblies are spun directly by the hex output shaft of the gearbox.
• These wheels allow the other two wheels on each side to spin as well.
• The wheels have multiple items bolted into them help the robot be able to drive.

Hex Hub

• A hub is a part that allows a wheel or mechanism to mount to a shaft.
• The center wheel assemblies have hex hubs that allow the wheels to spin with the output shaft the same way the gears do.

Pulleys

• The center wheel assembly includes two pulleys.
• Six bolts screw into the wheel to secure each pulley to the wheel.
• When tightening bolts in a circular pattern, first screw all of the bolts in loosley and then fully tighten them in a star like pattern, as shown here.

1 ➔ 2 ➔ 3 ➔ 4 ➔ 5 ➔ 6

Pulleys and belts

• The pulleys on the kit drivetrain are similar to gears. They are also toothed wheels.
• Unlike gears, pulleys aren’t designed to mesh with other pulleys. Instead, pulleys are designed to mesh with a timing belt.
• Similar to how the chain and sprockets on a bike work
• Belt and Pulleys allow you to connect parts over�a distance and have them spin together.

Corner Wheel Assembly

• The corner wheel assemblies are spun by belts when the center wheel assembly spins.
• The corner wheels don’t have hex hubs. Instead, they have 2 bearings one the wheel and one in the pulley.

Axle Bolts

• The corner wheel assemblies are mounted on axle bolts.
• These bolts don’t spin when the wheels spin.
• A nut on the bolt threads secures the bolt from moving.
• Only tighten these bolts/nuts until they don’t move side to side but can still spin in place.

Spacers

• Spacers are used to keep the wheel assemblies in position on their shafts.
• If the spacers aren’t installed, you would be able to slide the wheels side-to-side.

Things to remember

• This type of drive train turns by changing the direction and speeds of the wheels on each side of the robot.
• The gearbox converts the motors fast speed to a useable speed for the wheels.
• Gears and Pulleys are used to transfer rotation from the motors to the wheels
• Bearings allow shafts to spin smoothly. They reduce friction.
• A hub is a part that allows a wheel or mechanism to mount to a shaft.
• Spacers and E-Clips can be used to hold items in position on shafts.