0. FRC Concepts: Drivetrains
Team 1716 Redbird Robotics

4. 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

5. 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

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

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

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

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

11. Two Wheel Skid Pros Cons Dirt cheap Kitbot can be 2WD Simple to build
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

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

15. 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

17. 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

21. 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

25. 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

26. 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

30. 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)

36. Four Guidelines of Drivetrain Design
RRRR
Reliability
Repairability
Relevance
Resonability

37. Reliability Most important consideration Good practices
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)

38. 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)

39. 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

40. 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)

41. Resources www.chiefdelphi.com
FRC Drivetrain Design and Implementation PPT: