Date post: | 18-Jan-2016 |
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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