Building competitive manipulators

1. Building competitive manipulators Greg Needel DEKA R&D, Rochester Institute of technology Owner, www.midnightinvention.com Mentor teams: 131, 1511

2. Strategy, Strategy, Strategy! • Read the rules • Outline the game objectives • Look for the “gimmie” robot design • Try small simulators • Whatever you choose STICK WITH IT!

3. Types of Manipulators • Articulating Arms • Telescoping Lifts • Grippers • Latches • Ball Systems

4. D Arm: Forces, Angles & Torque • Example #1 - Lifting • Same force, different angle, less torque 10 lbs 10 lbs < D

5. Power • Power = Force x Distance / Time OR • Power = Torque x Rotational Velocity Power (FIRST def.) – how fast you can move something

6. Arm: Power Example • Same torque, different speed 10 lbs 10 lbs 0.2 HP, 200 RPM Motor w/ 1” sprocket OR 100 RPM w/ 2” sprocket 0.1 HP, 100 RPM Motor w/ 1” sprocket

7. Arm Design • “Arm”: device for grabbing & moving objects using members that rotate about their ends • Think of your materials (thin wall is good) • Every Pivot has to be engineered (less is more) • Linkages help control long arms. • Use mechanical advantage (it is your friend) • Think of the drivers (pivots on pivots are hard) • Operator Interface (keep this in mind)

8. 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, banebots.com )

9. Four Bar Linkage • Pin Loadings can be very high Watch for buckling in lower member Counterbalance if you canKeep CG aft

10. 4 bar linkage example :229 2005

11. Arm Example: 234 in 2001

12. Arm Example: 330 in 2005

13. Arm Example: 1114 in 2004

14. Telescoping Lifts • Extension Lift • Scissor Lift

15. Extension

16. Extension Lift Considerations • 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

17. Extension - Rigging Cascade Continuous

18. Slider (Stage3) Stage2 Stage1 Base Extension: Continuous Rigging • Cable Goes Same Speed for Up and Down • Intermediate Sections sometimes Jam • Low Cable Tension • More complex cable routing • The final stage moves up first and down last

19. Slider (Stage3) Stage2 Stage1 Base Extension: Continuous Internal Rigging • Even More complex cable routing • Cleaner and protected cables

20. Slider (Stage3) Stage2 Stage1 Base Extension: Cascade Rigging • Up-going and Down-going Cables Have Different Speeds • Different Cable Speeds Can be Handled with Different Drum Diameters or Multiple Pulleys • Intermediate Sections Don’t Jam • Much More Tension on the lower stage cables • Needs lower gearing to deal with higher forces • I do not prefer this one!

21. Team 73 in 2005 elevator

22. Scissor Lift

23. Scissor Lift Considerations • Advantages • Minimum retracted height - can go under field barriers • Disadvantages • Tends to be heavy to be stable enough • Doesn’t deal well with side loads • Must be built very precisely • Stability decreases as height increases • Loads very high to raise at beginning of travel • I recommend you stay away from this!

24. Team 158 in 2004

25. Arm vs. Lift

26. 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

27. 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)

28. Grippers • Gripper (FIRST def) grabbing game object • How to grip • How to hang on • Speed • Control

29. How to grip • Pneumatic linkage grip • 1 axis • 2 axis • Motorized grip • Roller grip • Hoop grip • Pneumatic grip

30. Pneumatic linear grip • Pneumatic Cylinder extends & retracts linkage to open and close gripper • 254 robot: 2004, 1-axis • 968 robot: 2004, 1-axis Recommended

31. Pneumatic linear grip • Pneumatic Cylinder, pulling 3 fingers for a 2-axis grip • 60 in 2004 Recommended

32. Motorized Linear Grip • Slow • More complex (gearing) • Heavier • Doesn’t use pneumatics • 49 in 2001 Not recommended

33. Roller Grip • Slow • Allows for misalignment when grabbing • Won’t let go • Extends object as releasing • Simple mechanism • 45 in 98 and 2004 Recommended

34. Hoop grip • Slow • Needs aligned • Can’t hold on well • 5 in 2000 Not recommended

35. Pneumatic Grip • Vacuum: • generator & cups to grab • Slow • Not secure • Not easy to control • Simple • Problematic Not recommended

36. Hang on! • Friction: High is needed (over 1.0 mu) • Rubber, neoprene, silicone, sandpaper • Force: Highest at grip point • Force = multiple x object weight (2-4x) • Linkage, toggle: mechanical advantage • Extra axis of grip = More control

37. Speed • Quickness covers mistakes • Quick to grab • Drop & re-grab • Fast • Pneumatic gripper • Not fast • Roller, motor gripper, vacuum

38. Grip control • Holy grail of gripping: • Get object fast • Hang on • Let go quickly • This must be done under excellent control • Limit switches • Auto-functions • Ease of operation

39. Latches • Spring latches • Hooks / spears • Speed & Control

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

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

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

43. 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

44. 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

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

46. Conveyors Why do balls jam on belts? • Sticky and rub against each other as they try to rotate along the conveyor Solution #1 • Use individual rollers • Adds weight and complexity Solution #2 • Use pairs of belts • Increases size and complexity Solution #3 - Use a slippery material for the non-moving surface (Teflon sheet works great)

47. Roller example: 188

48. Accumulator example: 173 & 254

49. Questions? Thanks to: Andy Baker (45) www.chiefdelphi.com www.robotphotos.org www.firstrobotics.net www.firstrobotics.uwaterloo.ca

50. Extra Stuff • Pneumatics vs. Motors • Materials • Shapes / Weights • Fabrication processes • Environment