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FRC Concepts: Drivetrains

FRC Concepts: Drivetrains. Team 1716 Redbird Robotics. Why are drivetrains important?. It moves a robot from point A to point B Not all drivetrain designs are equal each have advantages and disadvantages, and not all are entirely obvious

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FRC Concepts: Drivetrains

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  1. FRC Concepts: Drivetrains Team 1716 Redbird Robotics

  2. Why are drivetrains important? • It moves a robot from point A to point B • Not all drivetrain designs are equal • each have advantages and disadvantages, and not all are entirely obvious • A robot’s drivetrain is the most basic part of the robot • It MUST be reliable • A major consideration for pit scouting

  3. Rules of Drivetrain Design • Keep It Simple, Stupid • It’s a drivetrain, not a space station • Simple usually means reliable, too • It Must Meet Our Needs • Field and operating conditions are the two primary considerations for picking the type of drivetrain we will be going with

  4. Gearbox reduces speed, increases torque* Chain, gears, or pulleys transmit power to wheels Wheels turn How Power is Transmitted • Motors turn

  5. How a Drivetrain is Controlled Arcade One joystick controls direction Tank Two joysticks control either side of drivetrain

  6. Why YOU need to know all this • The engineering and scouting divisions need you to know what you’re talking about

  7. Common Drivetrain Styles • “Skid” Systems • 2WD, 4WD, 6WD, 6WD+ • Tank Treads/Belting • Traditional/WCD • Holonomic Systems • Swerve (Crab) • Mecanum

  8. Two Wheel Skid • Pros • Dirt cheap • Kitbot can be 2WD • Simple to build • Cons • Weak, can’t climb inclines well • Loses traction easily - if it gets into a pushing match with a robot, driving wheels may get pushed up above the floor • Noob tier

  9. Four Wheel Skid • Pros • Easier to control • Simple, more traction • The Bad • Turning is more difficult (both wheels have traction) • A compromise between stability and maneuverability • Still noob tier

  10. Six Wheel Skid • Middle wheel is offset, essentially creating two 4WD systems • Pros • Plenty of traction • Minimized resistance to turning due to middle wheel offset • Cons • Drivetrain “rocks” slightly due to middle wheel offset • Can be significant if robot has long arms and appendages

  11. 6+ Wheels/Tank Tread • More wheels = more distributed load • Pretty pointless in FRC • Traction not dependent on surface area • More wheels != more traction • Pushover tier • Complex and expensive for no good reason • Tank treads only useful if field elements make maneuvering downright diabolical

  12. West Coast Drive • Two wheels are driven directly by gearbox • No outer chassis rails • Wheels “cantilevered” outside the frame • Meaning: the wheel axle is attached at only one point, that point being the square metal tubing the axle is routed through • Pros • Easier to conduct maintenance on • Cons • Harder to implement as it requires precise machining

  13. Holonomic Drive Systems • Allows a robot to move in two dimensions, instead of just forward and backward • This allows it to rotate simultaneously • It can also do this WITHOUT rotating • Two major systems • Swerve/Crab • Mecanum/Omni

  14. Swerve • Each wheel can (at least theoretically) be independently driven and steered • In practice, arcade or tank drive is utilized to simplify steering • Pros • Highest maneuverability • Cons • Complex to build, maintain, code, and operate. Also quite heavy

  15. Mecanum/Omni • Uses vector addition to allow for omnidirectional motion • No complex steering mechanisms • Requires four independent wheels • Mass-produced parts make this drivetrain accessible (compared to swerve)

  16. Four Guidelines of Drivetrain Design • RRRR • Reliability • Repairability • Relevance • Resonability

  17. Reliability • Most important consideration • It’s the most important part of the robot • Good practices • Wheels be aligned properly • Reduce or remove friction wherever possible • Components must be manufactured to a high degree of quality and accuracy • Components must be durable (no wood or plastic)

  18. Repairability • It won’t be reliable 100% of the time, but it should be close • Good practices: • Accessibility • Have plenty of spare parts for quick repairs at competition • Maintenance and repair times should be quick (<10 min)

  19. Relevance • Everything on a drivetrain must be worth the work and risk of including it • Driving around in circles doesn’t require tank treads or swerve • Maneuvering around in tight spaces or climbing bumps in the game field may make one of them more worth it, however

  20. Reasonability • We have a limited amount of time and money during the build season • We have to allot our resources very carefully, and putting that time and money into something that won’t offer a good return is a bad idea • this is the reason we didn’t go swerve last year (we’d have to figure it out in only a few weeks)

  21. Resources www.chiefdelphi.com FRC Drivetrain Design and Implementation PPT: http://www.chiefdelphi.com/media/papers/download/2256

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