Manipulator and Appendage Design Andy Baker Sept. 2018

Andy Baker President and Owner, AndyMark FIRST Mentor since 1998 Mechanical Engineer, University of Evansville, ‘91 FIRST Championship WFA winner, 2003 28

Types of Manipulators Conveying and Gathering Collectors Ball (or object) Handling Ball shooting Winches Turrets Collectors Rollers Gripper Latch Vacuum Lifts Articulating Arms Telescoping Scizzor 27

Collectors Horizontal Roller High roller rpm, producing > robot’s driving speed Wide Funneling mechanism Outside or inside? 26

Collectors Horizontal Roller Outside Inside Better collecting ability Easier to break Inside Protected Weight saving Not defensible 25

Grippers Grabbing a scoring object (not a field component) Grab 1 item aka pick and place, aka touch it, grab it Speed to grab < 1 second Holding force > 2x object weight Designed-in sensors detect object presence Lightweight (usually on an arm or lift system) Robust: bend, not break Easily repairable (make many spares) High coefficient of friction w/ game piece, > 1 24

Grippers 23

Latches Grab field component (hanging bar, bridge, wall, etc.) Sometimes not legal! Failsafe, secure latch Often letting go after the match, but this needs to be done quickly Use a smart mechanism Spring loaded (preferred) Sensor met and automatic command given Use a manual lever, switch to let go 22

Articulating Arms Shoulder Elbow Wrist 21

Arm: Forces, Angles & Torque 10 lbs Example: Lifting at different angles Torque = Force x Distance Same force, different angle, less torque 10 lbs < D D 20

Arm: Power Example 125 Watts, 100 RPM 250 Watts, 200 RPM Same torque w/ Twice the Power results in Twice the Speed Power = Torque/ Time Be conservative: design in a safety factor of 2x or 4x 10 lbs 10 lbs 125 Watts, 100 RPM 250 Watts, 200 RPM 19

Arm: Design Tips Lightweight Materials: tubes, thin wall sheet Design-in sensors for feedback & control limit switches and potentiometers Linkages help control long arms KISS Less parts to build or break Easier to operate More robust Use off-the-shelf items Counterbalance Spring, weight, etc. 18

Anatomy of an Arm Aluminum or plastic structural tubing 4 bar Notes: Chain & belt tensioning challenge Watch robot rules for expanding outside frame perimeter Aluminum or plastic structural tubing 4 bar Motor / gearbox position choices Push rod Position and motion control sensors Counterweight or spring / latex tubing Game object sensors 17

Four Bar Linkage Pin loadings can be very high Watch for buckling in lower member Counterbalance if you can Cg moves forward & backward (watch tipping) Limited rotation Keeps gripper in known location 16

Telescoping Lifts Extension Lift Scissor Lift Motion achieved by stacked members sliding on each other Scissor Lift Motion achieved by “unfolding” crossed members 15

Extension Lift Considerations Drive cables up AND down, or add 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 the top 14

Extension - Rigging Cascade Continuous 13

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 Slider (Stage3) Stage2 Stage1 Base 12

Extension: Continuous Internal Rigging Even More complex cable routing Cleaner and protected cables Slider (Stage3) Stage2 Stage1 Base 11

Extension: Cascade Rigging Upward and Downward Moving 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 Slider (Stage3) Stage2 Stage1 Base 10

Purchased Elevator Lift Systems Many COTS versions available now 9

Scissor Lifts Advantages Disadvantages I do not recommend this! 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 do not recommend this! 8

Arm vs. Lift Feature Arm Lift Reach over object Yes No Fall over, get up Yes, if strong enough Go under barriers Yes, fold down Maybe, limits lift height Center of gravity (Cg) Not centralized Centralized mass Small space operation No, needs swing room How high? More articulations, more height (difficult) More lift sections, more height (easier) Complexity Moderate High Powerful lift Combination Insert 1-stage lift at bottom of arm  7

Conveying & Gathering Conveyor - device for moving multiple objects, typically within your robot Continuous Belts Use 2 at same speed to avoid jamming Individual Rollers Best for high traction balls, which can jam 6

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) 5

Ball System Tips More control is better Avoid gravity feeds – these WILL jam 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 The more capacity, the better 4

Ball Shooting Systems Secure shooting structure = more accuracy Feed balls individually, controlling flow Turret allows for aiming Sensors detect ball presence, direction Types: Single Wheel Double Wheel Catapult 3

Winches & Lifts Raise wheels with articulating arm Raise robot with winch (and lock it up) Design in a lock to prevent back drive 2

Turret Position fine tuning Must be VERY robust Difficult to repair Slow moving is ok Limited rotation (90-180 max) Belt / chain / gear drive Not for quick 1x scoring Good for stream shooting Good for placing over blocker 1

Thank you! 1