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

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vex drive systems

VEX Drive Systems

Presented by

Chani Martin

Lauren Froschauer

Michelle Gonzalez

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
drive wheels
Drive = Wheels

Small Wheel; 2.75

Traction on

smooth surfaces

Knobby Wheel; 5”

Good Traction rough

terrain or loose surfaces

All purpose wheel; 4”

Omni Wheels

GREAT for Turning

Allows robot to slide

easily

types of drive systems
Types of Drive Systems

Tank Drive

Crab Drive

Four Wheel

Omni- Drive

Holonomic

Six Wheel

Allows for Strafing

Better Turning

type of bases
Type of Bases

Drive train configurations

simple

rear wheel drive

simple

front wheel drive

simple

all wheel drive

simple

center drive

6 wheel

drive

other?

tracked drive

Taken from Base Fundamentals

Beach Cities Robotics – Team 294

Andrew Keisic

November 2009

There is no “right” answer!

swerve/ crab drive

choosing a drive system
Choosing a Drive System
  • When designing, choose a drive system that will match your strategy for the game
  • Will you need to strafe? (Holonomic, Crab)
  • 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

Chain and sprockets are

Related to gear ratios

the same way

as spur gears,

but are slightly more efficient

Gear Ratios
  • There are four VEX spur gears
  • 12 tooth
  • 24 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.
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 ;determine the direction of rotation of final gear
speed vs torque
Speed 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
examples

To calculate Gear Ratios

Divide the tooth

numbers of the

Driven/ Drive gear

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
compound gears
Compound Gears

Driven Gear

------------------

Drive Gear

Compound Gear Train- a gear train

with multiple levels of gears

Why? You can increase torque

Or speed with compound gears

Calculate Gear Ratio

12 tooth gear

12 tooth gear

X

=

------------------

------------------

60 tooth gear

60 tooth gear

1

1

1

Geared for

speed

---

X

---

=

---

5

5

25

more about turning
More About Turning

The Force Applied by

wheels must be

greater than resisting

force of friction between

wheels and ground

Torque= F* D

Tapplying= Fwheel* Width/2

Tresisting = Ffriction*Length/2

Red = Direction

Of Wheel Force

Force at Wheel=

torque of motor*

gear ratio*

radius of wheel

Ffriction= coefficient

of friction*

weight/ # of wheels

Green= Direction of wheel slip

base fundamentals

Base Fundamentals

Beach Cities Robotics – Team 294

Andrew Keisic

November 2009

center of gravity
Center of Gravity

A point in space where gravity acts

Why it’s important?

Determines the balance and stability of an object

center of gravity1
Center of Gravity

What robot is the most stable? The least?

How do you know?

What systems are inherently stable?

center of gravity2
Center of Gravity

Putting math behind intuition

Stability Triangle

α2

α1

h

b2

b1

center of gravity3
Center of Gravity

Limit of stability is determined by the CG location

In other words – the maximum ramp

angle of a stationary

robot

α2

α1

β2

β1

center of gravity4
Center of Gravity

Why keep it low?

Lowering the center of gravity maximizes alpha!

Stability Triangle

α2

α1

h

b2

b1

watch your center of gravity
Watch Your Center of Gravity

The bigger alpha is, the more stable the

Robot. 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
Ultrasonic Range Finder
  • Measures distances and locates obstacles/objects
  • Used in autonomous
optical shaft encoders
Optical Shaft Encoders
  • Measures direction of rotation and position of shaft
  • Used in calculation for speed of shaft and distance traveled
line trackers
Line Trackers
  • Allows robot to follow a black line on a white surface
  • Perfect for autonomously relocating
  • Usually, used three in a row
last thing
Last Thing
  • Your drive system is VERY important. No move = no win.
  • If your articulation shuts down in the middle of the match, you can still compete if your drive is built well!!!
  • Some teams neglect their drive, DON’T!
works cited
Works Cited
  • http://www.vexrobotics.com/
  • Google Images