Traction

Overview

  • From friction, we know
  • FF = μ · FN
  • If the applied force on an object is greater than the friction force, then the object will slide
    • Therefore if the torque on a wheel creates more force than the friction force, the wheel will slip
    • τ = F · d
    • Max pushing force for each wheel is when F = FF
    • FF = τ / d
    • If a wheel is not driven, it has no torque
      • Therefore, FF = 0 for un-driven wheels
  • As we just saw, all the wheels of the drivetrain share the robot weight
    • The amount each wheel supports (normal force) may be different
    • The total max drivetrain pushing force is the sum of the max pushing force of each wheel
    • Fpush = FF,1 + F,2 = μ1 · FN,1 + μ2 · FN,2
    • Therefore
      • Un-driven wheels reduces pushing force
      • Using a combination of low traction and high traction wheels reduces pushing force