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

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 Systems Tank Drive Omni- Drive Crab Drive Holonomic Four Wheel Six Wheel Allows for Strafing Better Turning

Type of Bases  Drive train configurations simple rear wheel drive simple front wheel drive simple all wheel drive simple center drive 6 wheel drive tracked drive There is no “right” answer! swerve/ crab drive other? Taken from Base Fundamentals Beach Cities Robotics – Team 294 Andrew Keisic November 2009

Choosing 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  Gear ratios  Sensors (autonomous)  Practice!!!  Gear ratios  Sensors (autonomous)  Practice!!!

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.  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. Chain and sprockets are Related to gear ratios the same way as spur gears

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. 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  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 Ratios Divide the tooth numbers of the Driven/ Drive gear

Red = Direction Of 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* D T applying = F wheel * Width/2 T resisting = F friction *Length/2 Force at Wheel= torque of motor* gear ratio* radius of wheel F friction = coefficient of friction* weight/ # of wheels More About Turning

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 h b2b2 b1b1 α1α1 α2α2

Center of Gravity  Limit of stability is determined by the CG location  In other words – the maximum ramp angle of a stationary robot β1β1 β2β2 α1α1 α2α2

Center of Gravity  Why keep it low?  Lowering the center of gravity maximizes alpha! Stability Triangle h b2b2 b1b1 α1α1 α2α2

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  Optical Shaft Encoders  Line Trackers

Ultrasonic Range Finder  Measures distances and locates obstacles/objects  Used in autonomous  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  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 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