Post on 30-Dec-2015
DRIVE BASE SELECTION
AN INTRODUCTION TO DRIVE TRAINS
WELCOME
Randy Hafner 2977 Sir LancerbotsAsst. CoachBuild/design mentor since 2009
INTRODUCTION
Terms Design considerations Drive Types Best Solution
TERMS
Wheelbase Friction/Coefficient of friction Torque Center of mass/gravity Power Gearing
Wheelbase
The distance from the center of the front wheel to that of the rear wheel in a motor vehicle, usually expressed in inches
Also distance from one side to the other
FRICTION
A force that resists the relative motion or tendency to such motion of two bodies or substances in contact.
Center of gravity The point in a system of bodies or an
extended body at which the mass of the system may be considered to be concentrated and at which external forces may be considered to be applied
Need to keep in mind as you design a drivebase
A low center of gravity allows use of more power
Center of gravity
Center of massThe point in a system of bodies or an
extended body at which the mass of the system may be considered to be concentrated and at which external forces may be considered to be applied
Need to keep in mind as you design a drivebase
A low center of gravity allows use of more power
Center of mass
Torque
The moment of a force; the measure of a force's tendency to produce torsion and rotation about an axis
Affects the ability to turn
Power Strength or force exerted or capable of
being exerted The availability of power determines
how much stuff your robot can do in a given span of time. Trade-off between doing a lot of stuff slowly or less stuff more quickly
GearingA system of gears and associated
elements by which motion is transferred within a machine
Gears Pulleys Sprockets Belts Chains
DESIGN CONSIDERATIONS
Motor selection Gearing Wheel type & size Weight
Motor selection FRC Approved list Torque CIM motors very popular
Gearing Power vs. speed Shifting gearbox?
Increased flexibility Increased complexity Increased cost
Pulleys & sprockets can also change gear ratio
Wheel Type & Size Traction Maneuverability Wheel size
Weight Limit by rules Acceleration vs. top speed
DRIVE TYPES Tank drive Omni drive Mechanum Swerve Drive Holonomic/Killough
Tank drive
2 WD 4 WD 6 WD 8+ Tank treads
2 WD
Caster
DrivenWheel
+ Easy to design+ Easy to build+ Light weight+ Inexpensive+ Agile
- Not much power- Will not do well on
ramps- Less able to hold
position
Motor(s)Motor(s)
4 WD
6 WD
8+ Wheels & Tank Treads
At this point more wheels increases complexity without giving significant advantage
Tank treads might be useful to crawl over an obstacle
Tank Treads
Omni Drive
Omni Drive
Mechanum
Mechanum
Mechanum
Swerve Drive
Swerve Drive
Swerve Drive
Holonomic/Killough
Holonomic/Killough
RESOURCES Know what:
You have available to you Money Time
You are capable of You have time for
Trade offs are necessary
CONCLUSIONS If you get the drive wrong nothing else
matters Your robot has to be in the right place at
the right time to be competitive The right drive is the one that best
compliments your team strategy
?’S