Robotics 101
Drivetrain and Framing
Possible configurations of a robot base, and pros and cons of each.
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:
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Wheels or Tracks
Motor or Engine
Transmission/Gearbox
Chains/Belts
• A robot needs a robust base and drivetrain to:
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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
COG
• Center of Gravity
− Mass concentration and where it is
acting on your robot
• Center of Turning
− Point at which the robot will rotate
about
WB
• Effective Wheelbase
− Wheelbase in contact with the ground
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
Belts or Chains:
Transfer
Power
To Wheels
• Linkage
Wheel
Wheel
Wheel
Gearbox
Motor
Motor
CIM Motors
Transmission/ gearbox
Motor
Motor
High traction wheels
Gearbox
Wheel
Wheel
Wheel
Gearbox Function
Gearbox Function:
Convert Motor Speed
to Wheel Torque through a series of
gears
2 speed shifting speed gearbox
Low gear = 6:1 ratio for pushing
High gear = 24:1 ratio for speed
Pneumatics used for shifting gears
Wheel
Wheel
Single speed gearbox
Standard KOP Ratio: 12:1
Torque From Motor Increased By 12X
Speed from Motor Reduced 12X
Motor
Wheel
Motor
• Gearbox
Drive Train Speed Calculator
Motor
RPM
Running
Drive to
Gear
Wheel
Robot
Box Sprocket Wheel Speed
Ratio
Ratio
Dia
ft/sec
3600
12
1
6
8
3600
24
1
6
4
3600
6
1
6
16
Team 1507’s Base and Drivetrain
• CAD demo of last year’s robot
• AndyMark Scavenger Hunt