FRC Concepts:DrivetrainsTeam 1716 Redbird Robotics

Why are drivetrains important?

● It moves a robot from point A to point B● Not all drivetrain designs are equal

o each have advantages and disadvantages, and not all are entirely obvious

● A robot’s drivetrain is the most basic part of the roboto It MUST be reliable

● A major consideration for pit scouting

Rules of Drivetrain Design

● Keep It Simple, Stupido It’s a drivetrain, not a space stationo Simple usually means reliable, too

● It Must Meet Our Needso Field and operating conditions are the two primary

considerations for picking the type of drivetrain we will be going with

How Power is Transmitted● Motors turn

● Gearbox reduces speed, increases torque*

● Chain, gears, or pulleys transmit power to wheels

● Wheels turn

How a Drivetrain is ControlledArcadeOne joystick controls direction

TankTwo joysticks control either side of drivetrain

Why YOU need to know all this

● The engineering and scouting divisions need you to know what you’re talking about

Common Drivetrain Styles● “Skid” Systems

o 2WD, 4WD, 6WD, 6WD+o Tank Treads/Beltingo Traditional/WCD

● Holonomic Systemso Swerve (Crab)o Mecanum

Two Wheel Skid● Pros

o Dirt cheapo Kitbot can be 2WDo Simple to build

● Conso Weak, can’t climb inclines wello Loses traction easily - if it gets into a pushing match with a robot,

driving wheels may get pushed up above the flooro Noob tier

Four Wheel Skid● Pros

o Easier to controlo Simple, more traction

● The Bado Turning is more difficult (both wheels have traction)o A compromise between stability and maneuverabilityo Still noob tier

Six Wheel Skid● Middle wheel is offset, essentially creating two 4WD

systems● Pros

o Plenty of tractiono Minimized resistance to turning due to middle wheel offset

● Conso Drivetrain “rocks” slightly due to middle wheel offset

Can be significant if robot has long arms and appendages

6+ Wheels/Tank Tread● More wheels = more distributed load

o Pretty pointless in FRC

● Traction not dependent on surface areao More wheels != more traction

● Pushover tiero Complex and expensive for no good reasono Tank treads only useful if field elements make maneuvering downright

diabolical

West Coast Drive● Two wheels are driven directly by gearbox● No outer chassis rails● Wheels “cantilevered” outside the frame

o Meaning: the wheel axle is attached at only one point, that point being the square metal tubing the axle is routed through

● Proso Easier to conduct maintenance on

● Conso Harder to implement as it requires precise machining

Holonomic Drive Systems● Allows a robot to move in two dimensions,

instead of just forward and backwardo This allows it to rotate simultaneouslyo It can also do this WITHOUT rotating

● Two major systemso Swerve/Crabo Mecanum/Omni

Swerve● Each wheel can (at least theoretically) be independently

driven and steered● In practice, arcade or tank drive is

utilized to simplify steering● Pros

o Highest maneuverability

● Conso Complex to build, maintain,

code, and operate. Also quite heavy

http://youtube.com/v/kZHaTGiakZM

Mecanum/Omni● Uses vector addition to allow for omnidirectional motion● No complex steering mechanisms● Requires four independent wheels● Mass-produced parts make this drivetrain accessible

(compared to swerve)

http://youtube.com/v/xgTJcm9EVnE

http://youtube.com/v/5vJCucpVdX0

Four Guidelines of Drivetrain Design

● RRRRo Reliabilityo Repairabilityo Relevanceo Resonability

Reliability● Most important consideration

o It’s the most important part of the robot● Good practices

o Wheels be aligned properlyo Reduce or remove friction wherever possibleo Components must be manufactured to a high

degree of quality and accuracyo Components must be durable (no wood or plastic)

Repairability● It won’t be reliable 100% of the time, but it

should be close● Good practices:

o Accessibilityo Have plenty of spare parts for quick repairs at

competitiono Maintenance and repair times should be quick (<10

min)

Relevance● Everything on a drivetrain must be worth the

work and risk of including ito Driving around in circles doesn’t require tank treads

or swerveo Maneuvering around in tight spaces or climbing

bumps in the game field may make one of them more worth it, however

Reasonability● We have a limited amount of time and

money during the build seasono We have to allot our resources very carefully, and

putting that time and money into something that won’t offer a good return is a bad idea

o this is the reason we didn’t go swerve last year (we’d have to figure it out in only a few weeks)

Resourceswww.chiefdelphi.comFRC Drivetrain Design and Implementation PPT:http://www.chiefdelphi.com/media/papers/download/2256