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VEX Drive Systems

VEX Drive Systems. 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?

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VEX Drive Systems

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

  2. 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

  3. Types of Drive Systems Tank Drive Crab Drive Four Wheel Omni- Drive Holonomic Six Wheel Allows for Strafing Better Turning

  4. 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

  5. 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)

  6. How to Optimize • Gear ratios • Sensors (autonomous) • Practice!!!

  7. Gear Ratios Chain and sprockets are Related to gear ratios the same way as spur gears • 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.

  8. 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

  9. 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

  10. 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

  11. 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

  12. Base Fundamentals Beach Cities Robotics – Team 294 Andrew Keisic November 2009

  13. Center of Gravity A point in space where gravity acts Why it’s important? Determines the balance and stability of an object

  14. Center of Gravity What robot is the most stable? The least? How do you know? What systems are inherently stable?

  15. Center of Gravity Putting math behind intuition Stability Triangle α2 α1 h b2 b1

  16. 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

  17. Center of Gravity Why keep it low? Lowering the center of gravity maximizes alpha! Stability Triangle α2 α1 h b2 b1

  18. 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.

  19. Sensors • Ultrasonic Range Finder • Optical Shaft Encoders • Line Trackers

  20. Ultrasonic Range Finder • Measures distances and locates obstacles/objects • Used in autonomous

  21. Optical Shaft Encoders • Measures direction of rotation and position of shaft • Used in calculation for speed of shaft and distance traveled

  22. Line Trackers • 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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