VEX Drive Systems Presented by Chani Martin Lauren Froschauer Michelle Presented by Chani Martin Lauren Froschauer Michelle.

VEX Drive SystemsVEX Drive Systems

Presented by

Chani Martin

Lauren Froschauer

Michelle

Presented by

Chani Martin

Lauren Froschauer

Michelle

What Are They? Why Are They Important?

What Are They? Why Are They Important?

The drive system of a robot is the maneuverable based on which the articulation is built.

Importance? If you’re robot doesn’t move, what’s the point? If your robot is too slow, you lose If your robot is too weak, you lose

The drive system of a robot is the maneuverable based on which the articulation is built.

Importance? If you’re robot doesn’t move, what’s the point? If your robot is too slow, you lose If your robot is too weak, you lose

Types of Drive SystemsTypes of Drive Systems

Tank Drive

Omni- Drive

Crab Drive

Holonomic

Four Wheel

Six Wheel

Allows for

Strafing Better Turning

Type of BasesType of Bases

Drive train configurations Drive train configurations

simplerear wheel drive

simplefront wheel drive

simpleall wheel drive

simplecenter drive

6 wheeldrive

tracked drive There is no “right” answer!

swerve/ crab drive other?

Taken from Base Fundamentals

Beach Cities Robotics – Team 294Beach Cities Robotics – Team 294

Andrew KeisicAndrew Keisic

November 2009November 2009

Choosing a Drive SystemChoosing a Drive System

When designing, choose a drive system that will match your strategy for the game

Will you need to strafe? (Holonomic) Will you need torque? Friction? (Tank) Will you need speed? ( four-six wheel) How about quick turns? (Crab, Omni)

When designing, choose a drive system that will match your strategy for the game

Will you need to strafe? (Holonomic) Will you need torque? Friction? (Tank) Will you need speed? ( four-six wheel) How about quick turns? (Crab, Omni)

How to Optimize How to Optimize

Gear ratios Sensors (autonomous) Practice!!!

Gear ratios Sensors (autonomous) Practice!!!

Gear RatiosGear Ratios

There are four VEX spur gears 12 tooth 36 tooth 60 tooth 84 tooth

A VEX motor has a certain amount of torque and speed without gearing. You can gear

your robot to be stronger or faster with certain gear ratios.

There are four VEX spur gears 12 tooth 36 tooth 60 tooth 84 tooth

A VEX motor has a certain amount of torque and speed without gearing. You can gear

your robot to be stronger or faster with certain gear ratios.

QuickTime™ and a decompressor

are needed to see this picture.

QuickTime™ and a decompressor

are needed to see this picture.

Chain and sprockets are Related to gear ratios the same way

as spur gears

Gear Ratios Cont. Gear Ratios Cont.

Driven/drive gear Drive gear= on the same axle as the

motor; drives the next gear Driven Gear= -_- Idle gears do not matter, we do not

factor them into gear ratio formula Idle gears= gears between drive and

final driven gear

Driven/drive gear Drive gear= on the same axle as the

motor; drives the next gear Driven Gear= -_- Idle gears do not matter, we do not

factor them into gear ratio formula Idle gears= gears between drive and

final driven gear

Speed Vs. TorqueSpeed Vs. Torque Driven/ drive gear Big gear/ small gear ; small gear drives big

gear , big gear turns slower than small gear= torque= power

Small gear/ big gear ; big gear drives small gear; small gear turns faster than big gear= speed

Driven/ drive gear Big gear/ small gear ; small gear drives big

gear , big gear turns slower than small gear= torque= power

Small gear/ big gear ; big gear drives small gear; small gear turns faster than big gear= speed

Examples Examples

Use the number of teeth 84/ 60 =7:5= big/ small = torque 12/84 = 1:7=small to big = speed Why? When the 60 tooth gear spins

once, the 84 tooth gear will spin less than once.

When the 84 tooth gear spins once, the 12 tooth gear will spin 7 times

Use the number of teeth 84/ 60 =7:5= big/ small = torque 12/84 = 1:7=small to big = speed Why? When the 60 tooth gear spins

once, the 84 tooth gear will spin less than once.

When the 84 tooth gear spins once, the 12 tooth gear will spin 7 times

To calculate Gear RatiosDivide the tooth numbers of the

Driven/ Drive gear

Red = DirectionOf Wheel Force

Green= Direction of wheel slip

The Force Applied by wheels must be greater than resisting force of friction between wheels and ground

Torque= F* DTapplying= Fwheel* Width/2Tresisting = Ffriction*Length/2

Force at Wheel= torque of motor* gear ratio* radius of wheel

Ffriction= coefficient of friction*weight/ # of wheels

More About TurningMore About Turning

Base Base FundamentalsFundamentalsBase Base FundamentalsFundamentalsBeach Cities Robotics – Team Beach Cities Robotics – Team 294294

Andrew KeisicAndrew Keisic

November 2009November 2009

Beach Cities Robotics – Team Beach Cities Robotics – Team 294294

Andrew KeisicAndrew Keisic

November 2009November 2009

Center of GravityCenter of Gravity

A point in space where gravity acts Why it’s important?

Determines the balance and stability of an object

A point in space where gravity acts Why it’s important?

Determines the balance and stability of an object

Center of GravityCenter of Gravity

What robot is the most stable? The least? What robot is the most stable? The least?How do you know?

What systems are inherently stable?

Center of GravityCenter of Gravity

Putting math behind intuition Putting math behind intuition

Stability Triangle

h

b2b1

α1

α2

⎟⎠

⎞⎜⎝

⎛= −

h

b111 tanα

⎟⎠

⎞⎜⎝

⎛= −

h

b212 tanα

Center of GravityCenter of Gravity Limit of stability is determined by the

CG location In other words – the maximum ramp

angle of a stationary robot

Limit of stability is determined by the CG location

In other words – the maximum ramp

angle of a stationary robot

⎟⎠

⎞⎜⎝

⎛== −

h

b2122 tanαβ⎟

⎠

⎞⎜⎝

⎛== −

h

b1111 tanαβ ⎟

⎠

⎞⎜⎝

⎛== −

h

b1111 tanαβ

β1β2

α1

α2

Center of GravityCenter of Gravity Why keep it low?

Lowering the center of gravity maximizes alpha!

Why keep it low? Lowering the center of gravity maximizes

alpha!Stability Triangle

h

b2b1

α1

α2

Watch Your Center of GravityWatch Your Center of GravityThe bigger alpha is, the more stable theRobot. Having either a large alpha and good turning ability are trade offs, just like torque and speed.

Sensors Sensors

Ultrasonic Range Finder

Optical Shaft Encoders

Line Trackers

Ultrasonic Range Finder

Optical Shaft Encoders

Line Trackers

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Ultrasonic Range FinderUltrasonic Range Finder

Measures distances and locates obstacles/objects

Used in autonomous

Measures distances and locates obstacles/objects

Used in autonomous

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QuickTime™ and a decompressor

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Optical Shaft EncodersOptical Shaft Encoders

Measures direction of rotation and position of shaft

Used in calculation for speed of shaft and distance traveled

Measures direction of rotation and position of shaft

Used in calculation for speed of shaft and distance traveled

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Line TrackersLine Trackers

Allows robot to follow a black line on a white surface

Perfect for autonomous relocation Usually, used three in a row

Allows robot to follow a black line on a white surface

Perfect for autonomous relocation Usually, used three in a row

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QuickTime™ and a decompressor

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