First fare 2011 manipulators

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  • 1. Manipulators for FIRSTFRC RoboticsBruce Whiteeld Mentor, Team 2471

2. Game pieces come in many sizes and shapes 3. Hanging Manipulate How ?Game objectives change each yearLiftingDumping ThrowingKicking Gathering 4. Know the possibilitiesThings that ManipulateLook on line, at competitionsManipulators thatTalk to mentors, teamswork for the gameThis seminarKnow the ObjectivesGame piecesGame & robot rulesYour game strategy Your Design Know your capabilitiesTools, Skills, Materials,Manpower , Budget , TimeManipulators you can build 5. Many Types of Manipulators Heavy lifting / Long reach Reoccurring o Articulating Arms themes in FIRST o Parallel arms o Telescoping Lifts games Gripperso Rollerso Clampso ClawsFIRST definition for Collect and Deliver a manipulator:o Accumulators & Conveyerso Turretso Shooters & Kickerso Buckets & Tables Device that Power & Control moves the gameo Wincheso Brakespiece from whereo Latches it is to where ito Pneumaticso Springs and Bungeeneeds to beo Gears & Sprockets 6. Articulating ArmsShoulder Elbow Wrist 7. Torque: Angle and Distance Torque = Force x Distanceo Same force, different angle = different torqueo Measure from the pivot pointo Motor & gearing must overcome torque W= 10 lbso Maximum torque at 90 degreesTorque = W x DTorque = W x D/2W=10 lbs1/2 DD 8. Power: Torque and Speed Power determines how fast you can move things Power = Torque / Time or Torque x Rotational Velocity Same torque with 2x Power = 2x Speed Or twice the arm length at same speed .3 ft Power 10 lbs 20 lbs 10 lbstrade 30 ft-lbs 60 ft-lbs os 425 100 RPM 50 RPM Probably dont wantWatts 1.6 rps .83 rps a 10 ft arm whippingaround at 1000 RPM 42.5 10 RPM 5 RPM Watts .16 rps .08 rps anyway 9. Motor Power: Assuming 100% power transfer efficiency: All motors can lift the same amount they just do it atdifferent rates. No power transfer mechanisms are 100% efficient Inefficiencies due to friction, binding, etc. Spur gears ~ 90% It adds up! Chain sprockets ~ 80% 2 spur gears + sprocket = Worm gears ~ 70% .9 x.9 x.8 = .65 Planetary gears ~80%Losing 35% of power to the drive train Calculate the known inefficiencies and then design in asafety factor (2x to 4x) Stall current can trip the breakers 10. Parallel Arms Pin loading can be very high Watch for buckling in lower arm Has limited range rotation Keeps gripper in fixed orientation 11. Parallel arm Fixed ArmJointed Arm 12. Arm Design Tips Lightweight Materials: tubes, thin wall Watch elbow and wrist weight at ends of arm Sensors for feedback & control limit switches, potentiometers, encoders Linkages help control long arms KISS your arm Less parts to build or break Easier to operate More robust Counterbalance Spring, weight, pneumatic, bungee Calculate the forces Watch out for Center of gravity Sideways forces when extended Model the reach & orientation 13. Telescoping Lifts Extension Lifts Motion achieved by stacked members sliding on each other Scissor Lift Motion achieved by unfolding crossed members 14. Extension Lift RiggingContinuous Cascade The final stage moves upfirst and down last.Previous stage speed plusown speedo Power vs. speedequations apply. Dontunderestimate the power.o Often needs brakes orratchet mechanism 15. Cascade Rigging Up-pulling and down-pullingcables have different speedsSlider Different cable speeds can behandled with different drum(Stage3)diameters or multiple Pulleys Intermediate sections dontStage2jam active return High tension on the lower stagecablesStage1 Base 16. Continuous Rigging Slider Cable goes same speed for (Stage3)up and down pulling cables Intermediate sectionssometimes jam Stage2 Lower cable tension More complex cable routing Stage1 Base 17. Continuous Rigging Internal Pull-down cable routed back onreverse route as pull-up cable Most complex cable routingSlider All stages have active return(Stage3) Cleaner and protected cables Stage2Stage1Base 18. Extension Lift Design tips Cables to drive up AND down, oradd a cable recoil device Segments must move freely Cable lengths must be adjustable Minimize slop and free-play Maximize segment overlap 20% minimum More for bottom, less for top Stiffness and strength are needed Heavy system, overlapping parts Minimize weight, especially at top 19. Scissor Lifts Advantages Minimum retracted height - can gounder field barriers Disadvantages Tends to be heavy when madestable enough Doesnt deal well with side loads Must be built very precisely Stability decreases as heightincreases Stress loads very high at beginningof travel Not recommend without priorexperience 20. Arms vs. LiftsFeatureArm LiftReach over objectYes NoFall over, get upYes, if strong enough NoComplexity ModerateHighWeight capacityModerateHighGo under barriersYes, fold downMaybe, limits lift heightCenter of gravity () CantileveredCentral massOperating spaceLarge swing space CompactAdding reach Difficult. More Easier. articulations More lift sectionsCombinations Arm with extender Lift with arm on top 21. Combinations Can work: Continuous direct drive chain runs stage 1 up and down No winch drum needed Cascade cable lifts slider stage Gravity return Got away with this only because slider GOG very well balanced on first stage Telescoping arm with wrist on slider stage to reach over objects2471 in 2011 22. Get a GripFIRST definition of a gripper:Device that grabs a game objectand releases it when needed.Design Concerns Methods Getting object into grip Pneumatic claws /clamps Hanging on 1 axis 2 axis Speed of grip and release Motorized claw or clamp Position control Rollers Weight and power source Hoop grips If at end of arm Suction 23. Claw or clamp Pneumatic One fixed arm reduce weight of claw Can make one or two moving sides768 in 2008 24. Pneumatic linear: 2 point clamp Pneumatic Cylinder extends &retracts linkage to open andclose gripper Combined arm and gripper Easy to manufacture Easy to control Quick grab Limited grip force 968 in 2004 25. Pneumatic linear 3 point clamp Pneumatic Cylinder, pulling 3 fingers for a 2-axis grip 60 in 2004 26. Motorized clamp Generally slower May be too slow for frequent grips Okay if few grabs per game of heavy objects More complex (gearing& motors) Heavier Tunable force No pneumatics 49 in 2001 27. Suction Grips Needs vacuum generator Uses various cups to grab Slow Not secure Not easy to control Simple Subject to damage ofsuction cup or game piecesNot recommended forheavy game piecesUsed successfully tocapture balls for kickers(Breakaway 2010) 28. Roller grips Allows for misalignment whengrabbing Wont let go Extends object as releasing Simple mechanism Have a full in sensor Many possible variations Mixed roller & conveyer45 in 2008 Reverse top and bottom rollerdirection to rotate object148 in 2007 29. Gripper designHang On! High friction needed Rubber, neoprene, silicone, sandpaper but dont damage game object Force: Highest at grip point Force = 2 to 4 x object weight Use linkages and toggles for mechanical advantage Extra axis of grip = More controlThe need for speed Wide capture window Quickness covers mistakes Quick to grab , Drop & re-grab Fast : Pneumatic gripper. Not so fast: Motor gripper Make it easy to control Limit switches , Auto-functions Intuitive control functions Dont make driver push to make the robot pull 30. Tube or post (recommended) Lazy Susan (not for high loads) Know when it is needed o One Goal = good o Nine Goals = not so good o Fixed targets = good o Moving targets = not so good Bearing structure must be solid Rotation can be slow Sensor feedback o Know which way it is pointing 31. Accumulator: Rotational device that collects objects Horizontal rollers: gathers balls from floor or platforms Vertical rollers: pushes balls up or down Wheels: best for big objects Can use to dispense objects out of robot Pointing the robot is aiming method in this case 32. Conveyer: For moving multiple objects Typically within your robot When game involves handling many pieces at onceWhy do balls jam on belts?- Stick and rub against each other as they try to rotate along the conveyorSolution #1- Use individual rollers- Adds weight and complexitySolution #2- Use pairs of belts- Increases size and complexitySolution #3- Use a slippery material for the non-moving surface (Teflon sheet works great) 33. Conveyer roller Examples 34. More control is better Avoid gravity feeds these are slow and WILL jam Direct the flow: reduce random movements. Not all game objects are created equal Tend to change shape, inflation, etc Building adaptive/ flexible systems Test with different sizes, inflation, etc. Speed vs. Volume Optimize for the game and strategy The more capacity, the better 35. Intake Rollers and Accumulators173 2471 36. Secure shooting structure = more accuracy Feed balls individually, controlling flow Rotating tube or wheel One wheel or two counter rotating 1771 in 2009 High speed & power: 2000-4000 rpm Brace for vibration Protect for safety Turret allows for aiming Sensors detect ball presence& shot directionNote CircularConveyer. Oneroller on insidecylindrical rollingsurface outside 37. Sudden release of power Use stored energy: Springs Bungee, Pneumatic Design & test a good latch mechanism Secure lock for safety Fast release 1 per game deployments 2011 minibot release 38. Use for dumping many objects Integrate with your accumulatorand conveyer Heavy ones may move too slow Usually pneumatic powered butcan run with gear, spring or winch 488 in 2009 39. 2010 Many uses Hanging Robots: 2000, 2004, 2010 Lifting Robots: 2007 Loading kickers 2010 Great for high torque applications Fits into limited space Easy to route or reroute 2004 Good Pull. Bad Push 40. Capture the cable Secure the cable routing Smooth winding & unwinding Leave room on drum for wound up cable Guide the cable Return cable or spring Must have tension on ca