robot drive trains - · pdf fileagenda drive drive trains pros/cons 1/5/2013 frc 4013 ftc 5070...

Robot Drive Trains Orlando Science Schools

FRC Kick Off 2013

Hector Barea

[email protected]

1/5/2013 FRC 4013 FTC 5070 1

mailto:[email protected]

Agenda

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• Drive Trains

– Differential Drive

– Ackermann Drive

– Skid (Tank) Drive

• Drive Trains Pros/Cons

– 2 Wheel Drive

– 4 Wheel Drive – 2 Gearboxes



– Tank Drive/Treads

– Others

• How to Choose Drive Train

Drive Train

• Is more important than anything else on the robot

• Fits strategy and game, can be built with existing resources

• Minimum maintenance, can be fixed in 10 minutes

• Balance between speed (no more than required, about 10

fps) and power, traction limited (avoid magic smoke)

• Use CIM motors for drivetrain

• Power all wheels (motor or chain)

• Test drive train with full robot weight, low CG

• Test early, break it early

• Give software and drive team time to test and practice

• Handling balance between ease of turning and straight line

driving (determined by drivers)

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• Control by wheels speed

(FLL robot)

• To move forward

– Both wheels move

forward

• To move backwards


backwards

• To turn

– Wheels moves at different

speeds

Differential Drive

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Robot

Ackermann Drive

• Wheels turn (car)

• To move forward


forward



backwards

• To turn

– Turn wheels

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Robot Robot

Information from

http://www.robotplatform.com/knowledge/Classification_of_Robots/wheel_control_theory.html



Skid (Tank) Drive

• Wheels skid (robot)

• To move forward


forward



backwards

• To turn

– Wheels moves at different

speeds

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Robot

Skid Drive

Straight Line Movement vs. Turning

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Robot

Robot

Track

Wheel Base

• Short wheel base robot is easier to turn

• Long wheel base robot is easier to drive

in straight line

2 Wheel Drive

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• Pros (+)

– Easy to Design

– Easy to Build

– Light Weight

– Inexpensive

– Agile

– Easy Turning

– Fast

– COTS Parts

• Cons (-)

– Not Much Power

– Does not do well on ramps

– Poor Pushing

– Susceptible to spin outs.

– Able to be pushed from the side

Gearbox Gearbox

Caster or

Omni

Motors can be driven in

front or rear

Position of Driven

Wheels:

1) Near Center of Gravity

for most traction

2) Front Drive for Max

Positioning

3) Lose Traction if

weight not over

wheels

Driven Wheels

* Presentation from FRC Team 1764

4 Wheel Drive – 2 Gearboxes

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• Pros (+)

– Easy to Design

– Easy to Build

– More Powerful

– Sturdy and stable

– Wheel Options • Omni, Traction,

Other

– COTS Parts

• Cons (-)

– Not Agile • Turning can be

difficult

• Adjustment Needed

– Slightly Slower

Chain or belt

Gearbox Gearbox

Driven Wheels

Driven Wheels

Position gearboxes

anywhere as needed

for mounting and

center of gravity

Position of Wheels:

1) Close together =

better turning

2) Spread Apart =

Straighter driving


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• Pros (+)

– Easy to Design

– Easy to Build

– Powerful

– Sturdy & Stable

– Many Options • Mecanum, Traction, Omni, Combo

– COTS Parts

• Cons (-)

– Heavy

– Costly

– Turning may or may not be difficult

• Options

– 4 traction • + Pushing, Traction, Straight

• - Turning

– All Mecanum; 2 traction & 2 Omni • + Mobility

• - Less traction, Less pushing

Gearbox Gearbox

Gearbox Gearbox

Types of wheels

determine whether

robot has traction,

pushing ability, and

mobility

If all traction wheels,

keep wheel base

short; difficult to turn.

Driven Wheels

Driven Wheels


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• Pros (+)

– Easy to Design & Build

– Powerful

– Stable

– Agile

– Turns at center of robot

– Pushing

– Harder to be high Centered

– COTS Parts

• Cons (-)

– Heavy & Costly

– Turning may or may not be difficult

– Chain paths

• Optional

– Substitute Omni Wheel sets at either end

• Traction: Depends on wheels

• Pushing = Great w/ traction wheels

• Pushing = Okay w/ Omni

Center wheel

generally larger or

lowered 1/8” - 1/4”

This is the

GOLD STANDARD

for FIRST

2 Ways to be

agile:

1. Lower Contact

on Center

Wheel

2. Omni wheels

on back, front

or both

Rocking isn’t too

bad at edges of

robot footprint, but

can be significant

at the end of long

arms and

appendages

Tank Drive/Treads

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• Pros (+)

– Climbing Ability • (best attribute)

– Great Traction

– Turns at Center

– Pushing

– Very Stable

– Powerful

• Cons (-)

– Energy Efficiency

– Mechanical Complexity

– Difficult for student build teams

– Turns can tear off treads

– WEIGHT

– Expensive

– Repairing broken treads.

Lower track at

center slightly to

allow for better

turning.

Holonomic Drive - Mecanum

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• Pros (+)

– Simple Mechanism

– High Maneuverability

– Immediate Turn

– Simple Control • 4 wheel independent

– Simple mounting and chains

– Turns around Center of robot

– COTS Parts

• Cons (-)

– Braking Power

– OK Pushing

– Suspension for teeth chattering

– Inclines

– Software complexity

– Drift (uneven weight distribution)

– Expense

Motor(s) Motor(s)

Motor(s) Motor(s)

For best results,

independent motor

drive for each wheel

is necessary.

Mecanum Wheels and Video

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http://www.youtube.com/watch?v=xgTJcm9EVnE



Holonomic Drive – Omni Wheels (Killough)

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• Pros (+)

– Turns around Center of robot

– No complicated steering methods

– Simultaneously used 2D motion and rotation

– Maneuverability

– Truly Any Direction of Motion

– COTS parts

• Cons (-)

– Requires 3-4 independently powered motors

– Weight

– Cost

– Programming Skill Necessary

– NO Brake

– Minimum Pushing Power

– Teeth Chattering (unless dualies)

– Climbing

– Drifting (Weight Distribution)

4-wheel

drive needs

square base

for

appropriate

vector

addition

3-wheel

drive needs

separated

120 degrees

for

appropriate

vector

addition

Omni Wheels and Video

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http://www.youtube.com/watch?v=03c3YuflQl4



Swerve (Crab) Drive

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• Pros (+)

– Maneuverability

– No Traction Loss

– Simple wheels

– Ability to hold/push

– NEW!: COTS

• Cons (-)

– Mechanically Complex

– Weight

– Programming

– Control and Drivability

– Wheel turning delay

All traction

Wheels.

Each wheel

rotates

independentl

y for steering

Swerve (Crab) Drive

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http://www.youtube.com/watch?v=ax_dtCUUKVU



Swerve (Crab) Drive

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• Generally speaking, the more mobile your robot

is, the less it can resist a push

More mobile less mobile

http://files.andymark.com/FIRST-Robotics-Drive-Systems.ppt









How to Choose Drive Train

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http://www.simbotics.org/files/pdf/drivetraindesign.pdf



Championship Drive Trains Statistics

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http://www.slideshare.net/oregonfirst/first-fare-2010-drive-trains











Roundtable Discussion and Questions

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