FIRST Robot Appendages

1
FIRST Robot Appendages

• Mark Koors, team 45
• Phil Perdan, team 135

2
Appendages Design

• Guidelines
• Off-Season Work
• Define Your Task
• Power Choices - Motor, Springs, Pneumatics
• Sample Appendage Analysis - Forklift
• Timing
• Debug
• Rules of Thumb
• Review

3
Guidelines

• Know FIRST rules stick to them
• Know your resources
• Materials, equipment, tools
• Design capabilities talent
• Reliability is key (KISS)
• Rely on a mentor ask for help
• Decide early and stick with it
• Take risks early try things out
• Watch your weight and shifting C.G.

4
Off-Season Work

• Study competition
• Study world around you
• Also works during build season
• Learn from mistakes

5
Define Your Task

• What do you want to do?
• Pick up a ball(s)
• Store balls
• Grab a goal(s) - Balance goals
• Release a goal(s)
• Lift a goal(s)
• Spin a bin
• Store a stack / Release stack

6
Power Choices

• Whats left after the drive??!!!!
• Motors
• Springs/Tubing
• Pneumatics
• How fast do I need to perform the task?
• What are the loads involved with the task?
• See motor selection white paper on Chief Delphi
• Choosing the Correct Motor by Mike Ciavaglia
• Use FIRST Motor Comparison as reference

7
Sample AppendageAnalysis - Forklift
From white paper on Chief Delphi page - Lifts
and Arms from SCRRF Workshops by Chris Huffman
8
Forklift - Advantages Disadvantages

• Advantages
• Can reach higher than you want to go
• On/Off Control
• Can be rigid
• Can be Actuated via Screw, Cable, or Pneumatics,
  though all involve some cabling
• Disadvantages
• Stability issues at extreme heights (SHIFTING CG)
• Cant Go Under Obstacles Lower Than Retracted Lift

9
Forklift - Design Considerations

• Should be powered down as well as up
• Segments need to move freely
• Need to be able to adjust cable length(s).
• Two different ways to rig
• MINIMIZE SLOP
• Maximize segment overlap
• Stiffness is as important as strength
• Minimize weight, especially at the top

10
Forklift - Calculations
Mslider
Fobject
Fslider1
Fhit
Dobject
Dslider

• Fobject Weight of Object Weight of Slider
• Dobject Distance of Object CG
• Mslider Fobject Dobject
• Fslider1 - Fslider2 Mslider / 2Dslider
• Fhit G value I use .5 (Weight of Object
  Weight of Slider)
• Mhitlower FhitHlower (Weight of Upper
  Weight of Lower) (Hlower / 2)
• Flower1 - Flower2 Mslider Mhitlower /
  2Dslider
• Mhit Fhit Hslider (Weight of Lift G
  value Hslider ) / 2
• Mbase Mslider Mhit

Fslider2
Hupper
Fupper1
Dupper
Hlower
Dupper/2
Fupper2
Hslider
Flower1
Mlower
Dlower
Dlower/2
Flower2
Mbase
11
Timing

• Drive base comes FIRST
• Start prototyping/testing of loads
• Any appendage used autonomously goes on second
  (Week 4)
• Test quickly - time is running out
• Keep driving non-competition drive bases after
  competition robot is shipped with prototype
  appendages
• Work on driver aids to make and add at competition

12
Debug

• Give electrical and software room time to work
• The earlier you break your robot, the earlier you
  fix your problems
• Prepare for tweaks at competition(s)
• FIRST fields vary and get used/abused
• Appendages get damaged
• Make spare parts as you go

13
Rules of Thumb

• Chains and belts - build in adjustment
• Watch CG shifts
• Give your drivers signals / hard stops for
  assistance and control
• Lights up when grabber is locked on goal
• Arm positional control with sensors
• Build it, break it, build it, break it, build it,
  build it, break it, WIN!
• See white paper on Chief Delphi page
• Lifts and Arms from SCRRF Workshops by Chris
  Huffman

14
Review

• KISS
• Know the limitations
• Rules, materials, machining capabilities
• Know your objective
• Write down all ideas
• Dont be afraid to try something
• When in doubt, ASK SOMEBODY for HELP
• Build and test quickly

HAVE FUN!!!!