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Robot Drive Trains Orlando Science Schools
FRC Kick Off 2013
Hector Barea
1/5/2013 FRC 4013 FTC 5070 1
Agenda
1/5/2013 FRC 4013 FTC 5070 2
• Drive Trains
– Differential Drive
– Ackermann Drive
– Skid (Tank) Drive
• Drive Trains Pros/Cons
– 2 Wheel Drive
– 4 Wheel Drive – 2 Gearboxes
– 4 Wheel Drive – 4 Gearboxes
– 6 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)
1/5/2013 FRC 4013 FTC 5070 3
• Control by wheels speed
(FLL robot)
• To move forward
– Both wheels move
forward
• To move backwards
– Both wheels move
backwards
• To turn
– Wheels moves at different
speeds
Differential Drive
1/5/2013 FRC 4013 FTC 5070 4
Robot
Ackermann Drive
• Wheels turn (car)
• To move forward
– Both wheels move
forward
• To move backwards
– Both wheels move
backwards
• To turn
– Turn wheels
1/5/2013 FRC 4013 FTC 5070 5
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
– Both wheels move
forward
• To move backwards
– Both wheels move
backwards
• To turn
– Wheels moves at different
speeds
1/5/2013 FRC 4013 FTC 5070 6
Robot
Skid Drive
Straight Line Movement vs. Turning
1/5/2013 FRC 4013 FTC 5070 7
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
1/5/2013 FRC 4013 FTC 5070 8
• 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
1/5/2013 FRC 4013 FTC 5070 9
• 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
4 Wheel Drive – 4 Gearboxes
1/5/2013 FRC 4013 FTC 5070 10
• 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
6 Wheel Drive – 2 Gearboxes
1/5/2013 FRC 4013 FTC 5070 11
• 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
1/5/2013 FRC 4013 FTC 5070 12
• 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
1/5/2013 FRC 4013 FTC 5070 13
• 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
1/5/2013 FRC 4013 FTC 5070 14
http://www.youtube.com/watch?v=xgTJcm9EVnE
Holonomic Drive – Omni Wheels (Killough)
1/5/2013 FRC 4013 FTC 5070 15
• 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
1/5/2013 FRC 4013 FTC 5070 16
http://www.youtube.com/watch?v=03c3YuflQl4
Swerve (Crab) Drive
1/5/2013 FRC 4013 FTC 5070 17
• 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
1/5/2013 FRC 4013 FTC 5070 18
http://www.youtube.com/watch?v=ax_dtCUUKVU
Swerve (Crab) Drive
1/5/2013 FRC 4013 FTC 5070 19
• 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
1/5/2013 FRC 4013 FTC 5070 20
http://www.simbotics.org/files/pdf/drivetraindesign.pdf
Championship Drive Trains Statistics
1/5/2013 FRC 4013 FTC 5070 21
http://www.slideshare.net/oregonfirst/first-fare-2010-drive-trains
Roundtable Discussion and Questions
1/5/2013 FRC 4013 FTC 5070 22