Drivetrain and FramingPossible configurations of a robot base, and pros and cons of each.

Robotics 101

Robot Base Overview

• The robot Base generally has three major components:− Frame− Drivetrain− Controls

• Robot base construction− Standard KOP frame

• Flexible, low cost, but heavy

− Custom designed thin gage aluminum• Very lightweight, not flexible to changes, built from CAD

• Good success with this style of base in past years

• Will use this base style again unless game requires something different− Climbing over obstacles, open front for collector mechanism, etc.

Robot Base Overview

• The robot “Drivetrain” has several major components:− Wheels or Tracks− Motor or Engine− Transmission/Gearbox− Chains/Belts

• A robot needs a robust base and drivetrain to:− Move quickly and efficiently− Push other robots out of the way− Precisely control where it is so that it can perform tasks− Provide stable base to mount scoring mechanism− Easy access to controls and battery change− Low center of gravity

• #1 Rule- Our robot should never tip over

Wheel Options

• Traction wheels- coefficient of friction close to 1− AndyMark standard KOP wheels

• Low cost, good traction, can’t replace tread

• Plastic wheel frame may break

− AndyMark Plaction wheels• Higher cost, excellent traction, replaceable tread

• Plastic wheel frame may break

− AndyMark Performance wheels• Much higher cost, excellent traction, replaceable tread

• Very durable

− VEXpro Colson wheels• Low cost, great traction, can’t replace tread

• Very durable for low price point

Wheel Options

• Lower Traction Wheels− Omni Wheels

• Low sideways friction (rollers), decent forward/reverse traction

• Very easy to push robot around− Used when turning is more important than pushing

− Mecanum Wheels• Rollers at 45 degree angle so robot can drive in all directions

• Highly maneuverable but easy to push robot around

• Difficult to program

Drivetrain Layout Principles

• Center of Gravity− Mass concentration

and where it is acting on your robot

• Center of Turning− Point at which the

robot will rotate about

• Effective Wheelbase− Wheelbase in contact

with the ground

WB

COG

COT

Axle Options

• Cantilevered • Side Supported

“Live”

“Dead”

Drivetrain Options

• 6 Wheel Tank Drive with “Dropped” Center Axles− Relatively easy to turn and drive straight

• Can turn in place with 2 CIM’s per side

− Most popular choice among FRC teams− Standard design for Team 1507

Drivetrain Options

• West Coast Drive (WCD)− Cantilevered Axles− Direct Drive to One Wheel, #25 Chain to other Live Axles− Hex Axles− Fast Removable Wheels− Welded Tube Chassis

Drivetrain Options

• 4 Wheel Swerve Drive − Robot can drive in all directions, incredibly maneuverable− Very complex to design, build, and program− Would require off-season to develop if we wanted to pursue this

option

Drivetrain Options

• 4 Wheel Omni Drive− Wheels 45 Degrees in Corners of

Chassis− Very Maneuverable− Loss of pushing force in all

directions compared to a tank drive

• Kiwi Drive− Wheels 120 Degrees apart− Very Maneuverable− Loss of pushing force in all

directions compared to a tank drive

Drivetrain Options

• Mecanum Drive− Wheels located in same orientation as a 4WD− Uses Force Vectors from wheel rollers to translate − Expensive− Fairly easy to build with COTs wheels− Difficult to program effectively− Requires a lot of Driver Training

Six Wheel Robot Base

• LinkageWheel

Wheel

WheelWheel

Wheel Wheel

Motor Motor

Gearbox

MotorMotor

Gearbox

High traction wheels

CIM Motors

Belts or Chains:TransferPower To Wheels

Transmission/ gearbox

Gearbox Function

• Gearbox Wheel WheelWheel

MotorMotor

Single speed gearboxStandard KOP Ratio: 12:1Torque From Motor Increased By 12XSpeed from Motor Reduced 12X

Gearbox Function:Convert Motor Speed to Wheel Torque through a series of gears

Motor RPM

Running

Gear Box

Ratio

Drive to Wheel

Sprocket Ratio

Wheel Dia

Robot Speed ft/sec

3600 12 1 6 8

3600 24 1 6 4

3600 6 1 6 16

Drive Train Speed Calculator

2 speed shifting speed gearboxLow gear = 6:1 ratio for pushingHigh gear = 24:1 ratio for speedPneumatics used for shifting gears

Team 1507’s Base and Drivetrain

• CAD demo of last year’s robot

• AndyMark Scavenger Hunt