Design Process

Guidelines

  • 3 ft/s: Very slow, very good pushing force
  • 4-7 ft/s: Slow
  • 8-12 ft/s: Medium, medium pushing force
  • 13+ ft/s: Hard to control, little pushing force
    • Teams have done it successfully, but it may require some fancy programming

Motor Curves

  • Very valuable source for designing mobility systems
  • Usually torque on x-axis, all other variables on y-axis
  • Max power the most important single characteristic
    • Motor can always be geared to get correct speed/torque
  • Check stall current; be careful if much higher than circuit breaker limit

Gearing

  • A simple pair of gearboxes will almost certainly be included in the kit
    • Very quick to build
    • May not be as powerful or flexible as other methods
  • DeWalt drill gearboxes
  • AndyMark gearboxes
    • Designed and built by two extremely experienced FIRST veterans
    • Two-speed, shift on the fly gearboxes
    • Adapters available for a variety of motors
    • AndyMark

Power Transmission

  • Keyways
    • Strong, hard to machine
  • Pins
    • Easy to machine, weak
  • Set screws
    • Can come loose easily; Loctite if using
  • Bolts
    • Very effective for large gears/sprockets, but annoying when connecting multiple things
  • Hex shafts
    • Very strong, easy to assemble
    • Gears, bearings available at AndyMark
    • Need a hex broach if using other gears/hubs
    • Can turn down shaft end to fit in bearings

Traction

  • Often the most important factor in determining pushing force
  • No metal or hard plastic cleats, etc. allowed
  • Supplied wheelchair wheels have quite low traction
  • Rubber treads or conveyor belting attached to wheels
    • Innovation First supplies pre-made traction wheels
  • Pneumatic wheels
    • Good for shock absorption
  • Test on actual carpet!
    • Too much traction can make it too hard to turn

Computer Aided Design

  • Use sketching tools to design drivetrain layout
  • 3D CAD model of drivetrain useful
    • Ensure quality of the final result
    • Easier to design functional attachments
    • Can be used for virtual prototyping

Testing and Practicing

  • Test beyond what the robot will likely experience
  • Test many times in different circumstances
  • Reinforce weak areas
  • Tweak components
  • Build spare parts for suspect components