Greg Needel Building competitive manipulators: Steps to successful design robot

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

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.

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

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

Torque Example  Lifting – Same force applied Different angle = less torque 10 lbs D D

Power  Power = Torque / Time Or  Power = Torque * Rotational Velocity  FIRST Def : How fast you can move something

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

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)

Types of Manipulators  Articulating Arms  Telescopic Lifts  Latches  Ball Conveyors  Shooters  Winches  Combination Mechanisms

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

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

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

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

Linkage Examples 340 in in 2007

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

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

Extension Lift Methods Continuous Cascade

Extension Lift Methods

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

Scissor Lifts 158 in in 2008

Arm vs. Lift FeatureArmLift Reach over objectYesNo Fall over, get back upYes, if strong enoughNo Go under barriersYes, fold downNo, limits lift potential Center of gravity (Cg)Can move it out from over robot Centralized mass over robot small space operation No, needs swing roomYes How high? More articulations, more height (difficult) More lift sections, more height (easier) ComplexityModerateHigh Accumulation1 or 2 at a timeMany objects CombinationInsert 1-stage lift at bottom of arm <-

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

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 )

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

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

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

Pneumatic Linkage Grip  Pneumatic cylinder extended 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

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

2- axis example  Center acting cylinder  3- points of contact Team 60 in 2004

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

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

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

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

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

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

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

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

Latch example: 267  Pneumatic Latch  2001 game  Grabs pipe  No “smart mechanism”

Latch example: 469  Spring- loaded latch  Motorized release  Smart Mechanis m  2003

Latch example: 118  Spring- loaded latch  Pneumatic release  Smart mechanism  2002

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

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

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

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

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

Roller example: 188

Accumulator example: 173 & 254

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

Engineering is Iterative research Design Prototype Test evaluate Final Design

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Questions? Greg Needel