DRIVE BASE SELECTION AN INTRODUCTION TO DRIVE TRAINS

WELCOME Randy Hafner 2977 Sir Lancerbots Asst. Coach Build/design mentor since 2009

INTRODUCTION Terms n Design considerations n Drive Types n Best Solution n

TERMS n n n Wheelbase Friction/Coefficient of friction Torque Center of mass/gravity Power Gearing

Wheelbase n n 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 n n n 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 mass 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 mass

Torque n n 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 n n 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

Gearing A system of gears and associated elements by which motion is transferred within a machine n Gears n Pulleys n Sprockets n Belts n Chains

DESIGN CONSIDERATIONS n n Motor selection Gearing Wheel type & size Weight

Motor selection n FRC Approved list Torque CIM motors very popular

Gearing n n Power vs. speed Shifting gearbox? n n Increased flexibility Increased complexity Increased cost Pulleys & sprockets can also change gear ratio

Wheel Type & Size n n n Traction Maneuverability Wheel size

Weight n n Limit by rules Acceleration vs. top speed

DRIVE TYPES n n n Tank drive Omni drive Mechanum Swerve Drive Holonomic/Killough

Tank drive n n n 2 WD 4 WD 6 WD 8+ Tank treads

2 WD Motor(s) Driven. W heel + Easy to design + Easy to build + Light weight + Inexpensive + Agile - Not much power - Will not do well on ramps - Less able to hold position Caster

4 WD

6 WD

8+ Wheels & Tank Treads n n 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

Mechanum

Swerve Drive

Holonomic/Killough

RESOURCES n Know what: n You have available to you n n You are capable of n You have time for Trade offs are necessary n n Money Time

CONCLUSIONS n n n 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