FTC Drivetrain Design Training Module

Module Goals

By the end, students should be able to:

Explain how drivetrain choice supports game strategy and mechanism design.
Compare differential, mecanum, X-drive, H-drive, and tread options for FTC.
Choose wheels, motors, gear ratios, and frame layouts based on performance goals.
Identify mechanical problems caused by poor alignment, weight distribution, or weak structure.
Use testing data to improve a drivetrain before competition.

Big Idea

The drivetrain is the robot's foundation

Move

Reach game pieces, scoring zones, and endgame areas quickly and controllably.

Align

Position the robot so intakes, lifts, and scoring mechanisms can do their jobs.

Support

Carry the robot structure, battery, electronics, and mechanisms without flexing or tipping.

A good drivetrain is not just fast. It is square, reliable, repairable, stable, and matched to the game.

Strategy First

Start with the game, not the wheels

Design questions

Does the robot need frequent sideways alignment?
Are there obstacles, ramps, seams, or crowded lanes?
Does the robot need to cross the field quickly or make short precise moves?
How much room must remain for the intake, lift, battery, and electronics?

Performance Goals

Write measurable requirements before building

Weak requirement

“Make a fast drivetrain.”

Better requirement

“Drive the scoring cycle path in under 8 seconds and align to the target within one robot width.”

Weak requirement

“Build something strong.”

Better requirement

“Run ten match-length sessions without chain/belt adjustment, loose wheels, or motor overheating.”

Interactive Check

Choose the best first drivetrain direction

A rookie FTC team has limited build time, needs to preserve motors for mechanisms, and wants reliable autonomous driving. What is the best starting point?

Choose one answer.

Differential / Tank

Simple, reliable, and strong forward/backward

Use for...

Reliability and fast construction
Game not requiring constant sideways alignment.
Reducing drivetrain motors
Autonomous paths with turns and arcs.

Watch out for...

Turning scrub, long wheelbases, and losing time when lining up sideways.

Mecanum Drive

Sideways movement for fast alignment

Advantages

Strafes directly sideways.
Moves diagonally.
Aligns quickly with scoring locations.
Supports flexible autonomous paths.

Tradeoffs

Uses four motors.
Strafing is weaker than forward driving.
Weight balance and programming matter more.

Advanced Options

X-drive, H-drive, and tracks are special-purpose choices

X-drive

Four omni wheels at angles. Omnidirectional, but mechanically unusual and needs vector programming.

H-drive

Differential drive plus a sideways strafe wheel. Useful sometimes, but the center wheel must contact the floor consistently.

Tracks

Strong contact area but heavier, higher friction, harder to turn, and more maintenance.

Interactive Sort

Sort each clue by drivetrain type

Saves motors and is easier to program

Cannot move directly sideways

Needs four independently driven wheels

Great for lateral scoring alignment

X-drive, H-drive, or tracks

Useful only when the game need justifies complexity

Differential

Mecanum

Special Purpose

Wheel Choice

Wheel type changes interactions

Traction Wheels

Best for pushing, acceleration, and simple differential drives. Too much traction can make turning harder.

Omni Wheels

Roll normally but slide sideways through rollers. Useful for reducing scrub or special holonomic drives.

Mecanum Wheels

Angled rollers combine wheel forces to create sideways and diagonal motion.

Wheel Diameter

Diameter affects speed, torque, clearance, and stability

Larger wheels

More theoretical speed at the same RPM.
More ground clearance.
Less force at the floor for the same wheel torque.
Often raise the robot higher.

Smaller wheels

Lower robot height.
More force at the floor for the same torque.
Easier packaging.
May struggle with obstacles or field seams.

Speed ≈ π × wheel diameter × wheel RPM ÷ 60

Interactive Reveal

Click each wheel type to reveal its best use

0 of 4 revealed.

Gear Ratio

Gear ratio trades speed for torque

More reduction

More wheel torque, better acceleration, easier control, and less stalling, but lower top speed.

Less reduction

Higher theoretical speed, but less wheel torque, more current draw under load, and harder control.

Choose the ratio that makes the complete robot controllable, not the ratio that looks fastest on paper.

Interactive Calculator

Estimate drivetrain free speed

Wheel diameter in inches Wheel RPM after gearbox

Enter values and calculate.

Actual speed will be lower because of load, friction, slip, roller losses, and battery voltage.

Torque at the Floor

Wheel force depends on torque and radius

The force of the wheel on the floor is determined by both torque and friction. If you go past the total possible force of friction the wheel slips and adding more torque does not help.

Useful relationships

Force ≈ torque ÷ wheel radius

Traction limit ≈ friction

Two Motors vs Four Motors

Motor count affects power, wiring, and mechanism options

Two-motor drive

Saves motor ports.
Simpler wiring and programming.
Good for differential drives.
Each motor carries more load.

Four-motor drive

More drivetrain torque and acceleration.
Usually required for mecanum.
Uses more motor ports.
More current, wiring, and setup.

Frame Geometry

The drivetrain should be square, rigid, and sized to strategy

Wide

Better sideways stability and more mechanism room, but harder in tight field spaces.

Long

More front/back stability, but can increase turning scrub for tank drives.

Compact

Navigates well, but tight size constraints and may be less stable.

Weight Distribution

Balanced weight makes driving more reliable

Careful Placement

Mount heavy components low and near the center when possible.

Balance

Balance left/right weight for straight autonomous movement.

Mecanum Considerations

Balance mecanum corners so every wheel grips.

Extensions

Slow the drivetrain when any extensions are out.

Interactive Check

Select the choices that improve drivetrain repeatability

Select the helpful design choices.

Power Transmission

How motor power reaches the wheels

Direct Drive

Few parts and easy troubleshooting, but wheel loads can stress gearboxes.

Chain

Strong, adjustable, and good for linking wheels, but needs tension and alignment.

Timing Belts

Quiet, light, and low maintenance, but require accurate center distance.

Gears

Compact and positive engagement, but require accurate spacing and support.

COTS Examples

Common starting points for FTC teams

REV Channel Drivetrain

Good for learning differential drive, chain/gears, and flexible channel construction.

REV Mecanum Drivetrain

Good for teams using the REV ecosystem and needing lateral movement.

goBILDA Strafer

Low-profile mecanum platform using independent wheel motors and common goBILDA parts.

Serviceability

A good drivetrain can be repaired quickly

Design access

Reach motor screws and connectors.
Replace wheels without disassembling the robot.
Keep chain/belt tensioners accessible.
Label motor ports and encoder wires.

Carry spares

Wheels, hubs, collars, bearings.
Chain, master links, belts, pulleys, sprockets.
Motor and gearbox spares.
Tools needed for the exact drivetrain.

Programming Impact

Mechanical choices change software difficulty

Differential control

Often uses arcade or tank drive with forward/backward and turn commands. IMU correction can improve straight driving.

Mecanum control

Combines forward, strafe, and turn. Field-centric control, heading hold, and speed modes can help drivers.

Testing

Test repeatability, not one good run

Drive tests

Forward, backward, turns, strafes, obstacles, and field paths.

Load tests

Final robot weight, lift raised, mechanism running, low battery.

Durability tests

Match-length runs, wall bumps, motor temperature, loose fasteners, chain/belt check.

Interactive Build Plan

Put the drivetrain testing steps in a good order

Click the cards in the order you would test them.

Required Quiz

Pass to complete the module

Each question is on its own slide.

Answer all 20 questions, then grade the quiz. Score at least 18 out of 20 to unlock the completion certificate.

Before the Quiz

Enter your name

Student name for certificate

This name will appear on your completion certificate.

Quiz Question 1

1 of 20

What is the main job of a drivetrain?

To make the robot look finished To move, align, and support the robot during the match To replace the need for drivers

Quiz Question 2

2 of 20

Why should drivetrain choice start with game analysis?

The best drivetrain depends on scoring paths, obstacles, alignment, and strategy The game does not affect drivetrain design Rules only matter after the robot is built

Quiz Question 3

3 of 20

Which drivetrain can move directly sideways when built and programmed correctly?

Standard tank drive Mecanum drive Two-wheel differential drive

Quiz Question 4

4 of 20

A six-wheel drop-center drive mainly helps a differential robot by:

Letting it fly over field walls Reducing turning scrub by pivoting near the center wheels Making all wheels mecanum wheels

Quiz Question 5

5 of 20

What is a major advantage of a two-motor differential drivetrain?

It saves motor ports for mechanisms It strafes better than mecanum It requires no programming

Quiz Question 6

6 of 20

What is a major tradeoff of a four-motor mecanum drivetrain?

It cannot turn It uses four motors and needs more programming/testing It has no alignment needs

Quiz Question 7

7 of 20

For a mecanum drivetrain, weight should be:

Balanced so all wheels contact the field well Placed only over one corner As high as possible

Quiz Question 8

8 of 20

What happens when drivetrain gear reduction is increased?

More wheel torque and less wheel speed More speed and less torque loss forever The robot no longer needs wheels

Quiz Question 9

9 of 20

Which wheel type has angled rollers that allow omnidirectional movement in a four-wheel setup?

Traction wheel Mecanum wheel Plain caster

Quiz Question 10

10 of 20

Which wheel type is useful for reducing scrub in some differential drivetrains?

Omni wheel Square wheel Unpowered gear

Quiz Question 11

11 of 20

A drivetrain frame that is not square can cause:

Better automatic alignment Uneven wheel loading and poor autonomous repeatability Free motor power

Quiz Question 12

12 of 20

Why should the battery usually be mounted low and near the center?

To improve stability and weight balance To make the robot taller To hide it from inspection

Quiz Question 13

13 of 20

What does chain drive allow a team to do?

Connect motor power to wheel shafts and potentially drive multiple wheels Avoid all maintenance Use mismatched sprockets freely

Quiz Question 14

14 of 20

What is one advantage of timing belts over chain when designed correctly?

They are usually quieter and lower maintenance They can use any center distance They never skip teeth under load

Quiz Question 15

15 of 20

What should teams test before calling a drivetrain competition-ready?

Only one short drive forward Repeated driving, turning, obstacle crossing, mechanism operation, and match-length runs Only the color of the wheels

Quiz Question 16

16 of 20

For a beginner FTC team prioritizing quick construction and reliability, a good first choice is often:

Two-motor six-wheel differential drive Uncontrolled track drive with no testing A drivetrain with no frame crossmembers

Quiz Question 17

17 of 20

Which drivetrain is usually best when the game rewards frequent lateral alignment and the team has time to tune it?

Four-motor mecanum A single caster One unpowered wheel

Quiz Question 18

18 of 20

What is a common cause of chain or belt failure?

Good alignment Incorrect tension, poor alignment, or rubbing on structure Using a square frame

Quiz Question 19

19 of 20

Field-centric mecanum control usually uses which sensor?

IMU Battery strap Zip tie length

Quiz Question 20

20 of 20

What is the best summary of drivetrain design?

Pick the fastest possible setup and ignore testing Choose a drivebase that fits the game, team skills, mechanisms, reliability needs, and repair plan Copy any robot without understanding it

Quiz Results

Grade the quiz

You need at least 18 out of 20 to unlock the completion certificate.

Not submitted.

After passing, advance to the final completion certificate.

5041 CyBear Robotics

Certificate of Completion

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Student Name

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FTC Drivetrain Design Training Module

Complete after passing the required quiz.