Designing Competitive Robot Manipulators: Steps for Success

1. Building competitive manipulators:Steps to successfully design a robot Greg Needel Mechanical Engineer Black & Decker

2. Introduction • What is a manipulator? • Active robot mechanisms (non drive train)‏ • The robot part that interacts with game pieces • Kinds of Manipulators • Latches • Arms • Grippers • Shooters

3. Strategize • Read the rules • Outline the game objectives • Choose your desired game strategy • Look for “Gimme” robot designs • Try small simulations. • Determine points (max, min, best guesses)‏ • Stick with your plan.

4. What's in the Kit? • How many motors? • Assign them a task • Drive train • Wrist • Arm • Other components • Linear bearings • Pneumatics

5. Torque • Torque = Force X Distance • The farther away something is, the harder it is to lift. • Torque is less important than power. 10 lbs D

6. 10 lbs D D Torque Example • Lifting – Same force applied • Different angle = less torque 10 lbs

7. Power • Power = Torque / Time Or • Power = Torque * Rotational Velocity • FIRST Def : How fast you can move something?

8. Power Example • Same Torque – different speeds 10 lbs 10 lbs 0.1 HP, 100 RPM Motor w/ 1” sprocket 0.2 HP, 200 RPM Motor w/ 1” sprocket

9. Power • Summary • All motors can lift the same amount (assuming 100% power transfer efficiencies) - they just do it at different rates • BUT, no power transfer mechanisms are 100% efficient • Inefficiencies (friction losses, binding, etc.)‏ • Design in a Safety Factor (2x, 4x)‏

10. Types of Manipulators • Articulating Arms • Telescopic Lifts • Latches • Ball Conveyors • Shooters • Winches • Combination Mechanisms

11. Articulating Arms • One or More Rotating Joints • Shoulder • Elbow • Wrist • This is the simplest form of Manipulator

12. Single Jointed Arms • One Shoulder Joint • Typically fixed end effectors • Easiest type to design and build • Follows KISS methodology 330 in 2005

13. Multiple Jointed Arms • Added degrees of freedom • Added complexity • Every joint needs to be engineered • How will the operator control the device? 234 in 2001

14. Linkages • Linkages help control arms • Advantages of specified motion • 4-bar (most common), The end always stay parallel • Can be customized for the application

15. Linkage Examples 340 in 2007 217 in 2007

16. Vertical Lifts • Extension Lifts • Motion achieved by stacked members sliding on each other • Scissor Lift • Motion achieved by “unfolding” crossed members.

17. Extension Lift • Movement within the robot dimensions • Extra weight due to required overlapping • Can be difficult to manufacture • Sections need to slide freely • Should be powered down AND up • If not, make sure to add a device to take up the slack if it jams • Segments need to move freely • Need to be able to adjust cable length(s). • Minimize slop / free-play • Maximize segment overlap • 20% minimum • more for bottom, less for top • Stiffness is as important as strength • Minimize weight, especially at the top

18. Cascade Continuous Extension Lift Methods

19. Extension Lift Methods

20. Scissor Lift • Maximum height with minimal space • Unstable at the top of motion • Complex to design and build

21. Scissor Lifts 1178 in 2008 158 in 2004

22. Feature Arm Lift Reach over object Yes No Fall over, get back up Yes, if strong enough No Go under barriers Yes, fold down No, limits lift potential Center of gravity (Cg)‏ Can move it out from over robot Centralized mass over robot Small space operation No, needs swing room Yes How high? More articulations, more height (difficult)‏ More lift sections, more height (easier)‏ Complexity Moderate High Accumulation 1 or 2 at a time Many objects Combination Insert 1-stage lift at bottom of arm <- Arm vs. Lift

23. Arm Advice • Materials • Thin wall can help reduce weight • High bending strength (except for plastics) • Every Pivot has to be engineered • Each rotation point will have different forces • Linkages help control long arms • Counter balance arms to reduce work on motors • Operator Interface (keep this in mind)‏ • How will the drivers control the arm

24. Arm Advice • K.I.S.S. doesn’t mean bad • Feedback Control is HUGE • Potentiometers, encoders, limits • Automatically Take Action Based on Error • Design-in sensors from the start of design • Think outside the box • Off the shelf components are good (andymark.biz, DeWalt transmissions, etc)‏

25. Braking: Prevent Back-driving • Ratchet Device - completely lock in one direction in discrete increments - such as used in many winches • Clutch Bearing - completely lock in one direction • Brake pads - simple device that squeezes on a rotating device to stop motion - can lock in both directions • Disc brakes - like those on your car • Gear brakes - applied to lowest torque gear in gearbox • Note : any gearbox that cannot be back-driven alone is probably very inefficient

26. Grippers • FIRST Def: a device that takes hold of a game object • How to Grip • How to Hang on • Advanced controls

27. How to Grip • Pneumatic Linkage Grip • One axis • Two axis • Motorized grip • Roller Grip • Hoop Grip • Suction Grip 768 in 2008

28. Pneumatic Linkage Grip • Pneumatic cylinder extends and retracts to open and close on the game object. • Multiple axis – The # of point of contact • Advantages • Quick grab and release • Easy to manufacture • Disadvantages • Requires pneumatic system

29. Single Axis Example • Center acting cylinder • 2- points of contact • Some alignment issues Team 968 in 2004

30. 2- axis example • Center acting cylinder • 3- points of contact Team 60 in 2004

31. Motorized Linear Grip • Gear driven linear grip • Mostly 1-axis grip • Advantages • Doesn’t require pneumatics • Tuned gripping force • Disadvantages • Tends to be slow • complex

32. Roller Grip • Uses rollers combined with a gripping action • Advantages • Good for fixing misalignment • Simple mechanism • Disadvantages • Problems releasing

33. Hoop Grip • Uses a flexible material to “cinch” the game object • Advantages • It will work • Disadvantages • Need precise alignment • Not active release 5 in 2000

34. Vacuum Grip • Advantages • Many different styles of vacuum tips available • Simple • Disadvantages • Need a vacuum device • Easily knocked free • Problematic

35. Hanging on • Friction – high coefficient needed • Over 1.0 mu • Rubber, Neoprene, Silicone, Sandpaper • Force: Highest at grip point • Force = multiple x object weight (2-4)‏ • Use linkages and mechanical advantage • Extra control - More axis of grip

36. Speed • Quickness covers mistakes • Quick to grab • Drop and re-Grab • Fast • Pneumatic Gripper • Not Fast • Motorized linear gripper, vacuum

37. Gripper Advice • Get the object fast • Hang on • Let go Quickly • Controls • The less the driver has to think about the better • Limit switches • Auto functions • Encoders

38. Latches • Small grippers typically for attaching to goals • Tips • Don’t depend on operator to latch use “smart mechanisms” • Must be able to let go quickly

39. Latch example: 267 • Pneumatic Latch • 2001 game • Grabs pipe • No “smart mechanism”

40. Latch example: 469 • Spring-loaded latch • Motorized release • Smart Mechanism • 2003

41. Latch example: 118 • Spring-loaded latch • Pneumatic release • Smart mechanism • 2002

42. Latching advice • Don’t depend on operator to latch, use a smart mechanism • Spring loaded (preferred)‏ • Sensor met and automatic command given • Have a secure latch • Use an operated mechanism to let go • Be able to let go quickly • Pneumatic lever • Motorized winch, pulling a string

43. Ball Systems • Accumulator = rotational device that pulls objects in • Types: • Horizontal tubes - best for gathering balls from floor or platforms • Vertical tubes - best for sucking or pushing balls between vertical goal pipes • Wheels - best for big objects where alignment is pre-determined

44. Conveying & Gathering • Conveyor - device for moving multiple objects, typically within your robot • Types: • Continuous Belts • Best to use 2, running at the same speed to avoid jamming • Individual Rollers • Best for sticky balls that will usually jam on belts and each other

45. Conveyors Rollers • Use individual rollers • Adds weight and complexity Double Belts • Use pairs of belts • Increases size and complexity Single Belt - Use a slippery material for the non-moving surface

46. Ball System Tips • More control is better • Avoid Gravity feeds • Try to reduce “random” movements • Not all Balls are created equal • Balls tend to change shape • Building adaptive/ flexible systems • Speed vs. Volume • Optimize for the game and strategy

47. Roller example: 188

48. Accumulator example: 173 & 254

49. Ball Advice • Always have control of the balls • Gravity Feels will jam • The more capacity the better.

50. Design is an Iterative Process Final Design