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Drive Systems

By: David Gitz, EE, Electrical/Programming Team Mentor FRC #1208. Drive Systems. Audience:. Programming Team Members Electrical Team Members. Topics. Wheels 2WD/4WD 6WD/West Coast Track Holonomic/Mecanum Crab/Swerve. Wheels [2]. Swivel Caster. Ball Caster. KoP Wheel.

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Drive Systems

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  1. By: David Gitz, EE, Electrical/Programming Team Mentor FRC #1208 Drive Systems

  2. Audience: • Programming Team Members • Electrical Team Members

  3. Topics • Wheels • 2WD/4WD • 6WD/West Coast • Track • Holonomic/Mecanum • Crab/Swerve

  4. Wheels [2] Swivel Caster Ball Caster KoP Wheel Plaction Wheel Omni-Wheel Mecanum Wheel

  5. simple rear wheel drive simple front wheel drive simple all wheel drive simple center drive 6 wheel drive other? tracked drive Configurations [3] 2WD 4WD 6WD swerve/ crab drive Omni/Mecanum

  6. 2 Wheel Drive • The Good • Cheap; Kitbot is 2WD • Very simple to build • The Bad • Easily spins out • Difficulty with inclines • Loses traction when drive wheels leave floor

  7. 4 Wheel Drive • The Good • More easily controlled • Pretty simple to build • Better traction • The Bad • Turning in place is more difficult • Compromise between stability and maneuverability

  8. 6WD/West Coast [3] • Typically, one wheel is offset from the others to minimize resistance to turning • Rocking creates two 4WD systems, effectively • Typical offset is 1/8” – ¼” • Rock isn’t too bad at edges of robot footprint, but can be significant at the end of long arms and appendages • One or two sets of omniwheels can be substituted for offset wheels.

  9. Tracked [3] • Pushing power increased • Mechanically more complicated • Need to have adequate track tension • Throwing a track and/or breaking one can be easy and very hard to fix • Slower, much more power intensive • Applications • HEAVY duty pushing • Climbing

  10. Omni/Mecanum • Mechanically as complicated as a 4WD System • A lot of times can substitute normal wheels for Omni/Mecanum in tight situations. • Less pushing power, more maneuverable • Control can be more complicated (especially with Mecanum) • More parts that can break

  11. Crab/Swerve [3] • Extremely mechanically and program complex • Lots of parts to make/buy/fix • Highly maneuverable • Requires (normally) precise engineering • Takes up a lot of space, uses a lot of motors • Pure 4-Crab: 5 • Pure 4-Swerve: 8!

  12. Other Information • Steering vs. Drive Systems • In FRC, there are no “Tank” Drive Systems. There is Tank Steering and Track Drive Systems. These terms are NOT interchangeable. • Tank Steering: • Uses 2 Joysticks, Left Joystick controls speed of Left motors, Right Joystick controls speed of Right motors. • Arcade Steering: • Uses 1 Joystick, controls speed of Left and Right motors together.

  13. References • http://www.usfirst.org/roboticsprograms/frc/content.aspx?id=10934 • http://www.andymark.biz • Drivetrain_Fundamentals_v2.1 • FRC_Drive_Train_Design_and_Implementation

  14. Questions?

  15. Homework • 1. Describe the Drive Train FRC Team #1208 (us…) used in the FRC 2010 Competition. • 2. Name 1 advantage and 1 disadvantage of using a Meccanum Drive System. • 3. What is the difference between Tank Steering and a Track Drive System?

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