Transcript VEX Drive Systems

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?
 If your robot is too slow, you lose
 If your robot is too weak, you lose
Drive = Wheels
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Knobby Wheel; 5”
Good Traction rough
terrain or loose surfaces
Qui ckT ime™ and a
dec ompress or
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Small Wheel; 2.75
Traction on
smooth surfaces
Omni Wheels
GREAT for Turning
Allows robot to slide
easily
All purpose wheel; 4”
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Types of Drive Systems
Tank Drive
Crab Drive
Four Wheel
Omni- Drive
Holonomic
Six Wheel
Allows for
Strafing
Better Turning
More Drive Systems
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Taken from Base Fundamentals
Beach Cities Robotics – Team 294
Andrew Keisic
November 2009
Type of Bases
 Drive train configurations
simple
rear wheel drive
simple
front wheel drive
simple
all wheel drive
tracked drive
swerve/
crab drive
other?
simple
center drive
6 wheel
drive
There is no “right”
answer!
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
 Gear ratios
 Sensors (autonomous)
 Practice!!!
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.
 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
 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
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
Driven Gear
-----------------Drive Gear
Compound Gears
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
-----------------60 tooth gear
X
1
1
1
--- X --- = --5
5
25
12 tooth gear
-----------------60 tooth gear
=
Geared for
speed
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
Green= Direction
of wheel slip
Force at Wheel=
torque of motor*
gear ratio*
radius of wheel
Ffriction= coefficient
of friction*
weight/ # of wheels
Base
Fundamentals
Beach Cities Robotics – Team
294
Andrew Keisic
November 2009
Center of Gravity
 A point in space where gravity acts
 Why it’s important?
 Determines the balance and stability of an
object
Center of Gravity
 What robot is the most stable? The least?
How do you know?
What systems are inherently stable?
Center of Gravity
 Putting math behind intuition
Stability Triangle
α2
h
α1
 b1 
1  tan  
h
1
 b2 

h
 2  tan1 
b1
b2
Center of Gravity
 Limit of stability is determined by the
CG location
 In other words – the maximum ramp
angle of a stationary
robot
α1
β1
b 
1  1  tan  1 
h
1
α2
β2
 b2 

h
 
 2   2  tan1 
Center of Gravity
 Why keep it low?
 Lowering the center of gravity maximizes
alpha!
Stability Triangle
α2
h
α1
b1
b2
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
 Ultrasonic Range Finder
 Optical Shaft Encoders
 Line Trackers
Ultrasonic Range Finder
 Measures distances and locates
obstacles/objects
 Used in autonomous
Optical Shaft Encoders
 Measures direction of rotation and position
of shaft
 Used in calculation for speed of shaft and
distance traveled
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
 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
 http://www.vexrobotics.com/
 Google Images