drive base selection an introduction to drive trains

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

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