BEST Robotics Overview “Game Rules” provide the excitement – Also the task definition and reason for strategy – Usually “move this object from here to there” Robot movement; Game object movement/gripper “Box of parts/junk, some assembly required” – Provide Real World constraints, (no unobtainium) – Level playing field, same and free to schools – R-kit is returned unmodified; C-Kit is consumable Ideas are also constrained by craftsmanship – BEST is Student Built! – Expect poor craftsmanship, keep it simple. 7/7/20151Joel Graber

Dallas BEST Schedule 8-9am snacks, Early Rkit release, Hack-saw challenge, this rotating 9am Program starts, ending with Game Demo, Q&A Training Breakout sessions, –Easy C for beginners (max 2/team), Notebook and Marketing training (max 2/team) –Rkit distribution and self-inventory, Ckit distribution Build training, build sessions running in shifts –Stagger your breaks during build session to get some lunch Kick-Off – Mesquite Technology Excellence Center Week 0 Sept 26 today!  Declaration of intent to enter BEST award due Week 4 Oct 23  Demo Day – North Mesquite High School Week 5 Oct 31  Deadline for Notebook, Demographics Forms Due  Check-In for Dallas BEST Week6 Nov 6 4-9pm  Dallas BEST 2015 Game Day Nov 7 8:00 AM Eastfield College

Keep these for Build session Aluminum Block to make motor hub ½” plywood to make wheels Rkit to plug it together Motor mount aluminum plates with holes in them Lunch is on your own (unless you signed up for pizza) Build training starts at 11:30 and 12:30 for staggered shifts 7/7/2015Joel Graber3

Mechanisms (engineering) Defined: (wikipedia) an assembly of moving parts performing a complete functional motion, often being part of a large machine; linkage. Explained: a device designed to transform input forces and movement into a desired set of output forces and movement. Mechanisms generally consist of moving components : linkages belt and chain drives cam & follower gears and gear trains structural components : Frame Fasteners Bearings springs 7/7/20154Joel Graber

Frame(Body or Chassis) Compression: Plywood, 1x4 wood PVC pipe & fittings Aluminum sheet Cardboard Plastic sheets Fasteners: – Screws – Bolt/nut/washer – Wood Glue, Epoxy – Duct Tape – Paper clips – Zip ties 7/7/2015Joel Graber5 Tension only: String copper wire Brake Cable Pipe hang tape Igus chain Piano wire pushrod

PVC as Frame Material Good for low tool use, cut with scissor type = no waste or dust Lots of material provided, cheap to replace Start with press fit, or with screws Can glue when final Can be heat bent, or fittings only 7/7/2015Joel Graber6

PVC Frame example Layout and testfit dry Then Screw or Glue 7/7/2015Joel Graber7

Wood as Frame Material Takes screws and glues well Dusty to cut in classroom Glue Lam method: – 1 day with table saw to cut up everything in to fractal pieces – Hand assemble and glue/screw without more tools, or only small cross cuts – Popsicle/craft sticks are extreme version Prototype 1:1 scale cardboard then cut exact shape with Jigsaw 7/7/2015Joel Graber8

Glue-Laminated Plywood Frame 1 hour with Table saw to cut up plywood into fractal pieces, then low additional cutting in classroom 7/7/2015Joel Graber9 Partially assembled modular approach Arm module can be detached and moved later Base/Arm/Modules can be redone without redoing all

Chassis, drive base Differential drive is typical – Short Wide turns better than Long Skinny Caster : pulley, skate wheel, bearing, hole saw plug, turntable, bolt, threaded rod Slider: PVC elbow, formed plastic Golfball slide/rotate; align slide with more power angle 7/7/201510Joel Graber

Motor Power = Speed * Torque Torque unit examples: – Radius * Weight – Eg Weight hanging cable drum with Radius – Meter * Newton for metric – Foot * pounds for motors – Ounce * inches for servos Torque  Current Power = Speed * Torque – Power is zero if speed is zero – Power is zero if torque is zero – Power out is max at 50% – 17W = 60 rpm*2 ft-lbs – Speed max at no load (0 T) – Torque max at no 0 rpm Electric to Work Efficiency – Affects battery life – Peaks at lower % than Power – Mostly don’t care for BEST Max power point is ~50% torque, 50% speed 7/7/201511Joel Graber

Motor Power at max power 2 BEST Large motors: ¼” shaft - Power = 43*23 = 989 RPM * inch * lbs – in*lbs of torque -Power = 21*12 = 252 RPM * inch * lbs (100%) 2 BEST Small motors: ¼” shaft - Power = 90*9.5 = 855 RPM * inch * lbs – in*lbs -Power = 45*4.7 = 213 RPM * inch * lbs (85%) -4 Servos: spline output to servo horn -Power = 53 * 3.5 = 188 RPM * inch * lbs * lbs eqv -Power = 25 * 1.75 = 44 RPM * inch * lbs (18%) 7/7/2015Joel Graber12

Axle Hubs (1/4) Large Motor has 23 in * lbs Stall torque ¼” = 0.125” radius shaft 23 in*lbs / 0.125” = 184 lbs! (big) D- flat delta radius = 0.030” Flat length = 0.500” Area = in sq (tiny) PSI = 184/0.015 = ~12000 lb/in^ Aluminum PSI =~30000 (whew) – Rockwell hardness = A40 Alloy Set screw: 170,000 PSI, C37 7/7/2015Joel Graber13

Large Motor has 23 in * lbs of torque 23 lbs isn’t too bad, so we need to spread the output torque over an inch or more, so that lesser materials like wood or plastic can handle it. 7/7/2015Joel Graber14 Axle hubs (2/4)

Axle Hubs (3/4) #10-32 x 1” allen headed set screw tapped hole ¼” shaft hole Al ½” bar cut to 2x2” Wheel/arm mounting holes, 2 or more; Motor mount screw tightening hole (optional) 7/7/2015Joel Graber15

No-Tap hub (4/4) #10-32 x 1” allen headed set screw ¼” setscrew hole (not tapped!) #10 hex nut 3/8” cross nut hole Can be made with just one step-drill bit of size ¼”-3/8” 7/7/2015Joel Graber16

Shaft to shaft couplers Could use 2 axle hubs face to face, or this shaft coupler of Aluminum bar set-screw or pin Setscrew 7/7/2015Joel Graber17 Motor

Hardest parts to build Used to spread force from hardened steel axles to softer materials like wood and plastic” – Torque calculations: 6ft-lbs x ¼” = PSI? Machined aluminum blocks – Motor hubs – Shaft joiner Drill most of the holes first, cut last Reportedly can be cut with a vise & hacksaw – but may require social engineering, relay team of 4, doing 30sec intervals time competition against previous team. 7/7/201518Joel Graber

Motor tradeoff Both L,S motors have ¼” shaft Exchangeable unit is motor mount plate Traditionally, Large motors used for wheels, – Good for ramp games, – Bigger wheels make robot faster Small motors can be used for wheels Arms usually need more torque anyway 7/7/201519Joel Graber

Demo wheel motor choice Motor selection vs wheel speed 6” wheels on both robots – Who wins race Change wheels – Now who wins? Side effects of wheel size – Ground clearance, COG, Length – Vision obstruction 7/7/2015Joel Graber20

Dallas BEST 2014 Rookie Build Session 21 Igus Spherical bearings vs RAZZ ball bearings The usual Igus parts bag is late, may not make kickoff. Axle (1/4” rod) RAZZ ball bearing IguBall spherical bearing RAZZ ball bearing Stronger (made of steel) ball bearings (rotates easily) Requires nested pocket Requires retainer (or shaft nut) Difficult to align 2 correctly Igus Iguball bearing Light weight Self-lubricating nylon sleeve Use with drylin black rod Built in mount & retainer Sphere self-aligns +/- 10 °

Moving Components (1/2) linkage examples – Arm(Lever), pushrod, 4-bar, bellcrank belt and chain drive examples: – Round belt in Rkit Pulley kit (1:5) – Flat belt in Rkit Pulley kit (1:??) – String drum to Arm wheel (1:???) – Pulley or smooth surface to change string direction 7/7/2015Joel Graber22

Moving Components (2/2) Gears train examples: – Woodgears.ca template on plastic sheet – Use 12mm or bigger teeth – Use ~ 12 tooth min for smallest gear as smaller gears have more friction 7/7/2015Joel Graber23

Gear Ratios or Leverage Work = force * distance Constant Work = big force * short distance = small force * large distance Wheels – Large wheels are Fast but Weak cant climb ramps or push hard Can roll over bumps more easily – Small wheels are Slow and Strong Can climb ramps, but move slowly 7/7/2015Joel Graber24

Belt and Pulley Proper tension is important Failure point is usually slipping on the small gear Avoid slipping by using idler to get extra wrap Small pulley has D to match motor shaft Both have clamps to keep from falling off But clamp does not transmit much torque! 7/7/201525Joel Graber

Dallas BEST 2014 Rookie Build Session 26 Notes on toothed Pulleys Do not do any drilling on the pulleys – No holes in the large pulley, no change to the set screws. – Plastic idler pulley may only be used with shoulder bolt. – Do not modify the round belt, – only straight 3’ belt may be modified – Pulley set may be unreliable unless idler is used to get extra wrap on small drive pulley. – Proper belt tension is also important. <8 of 18 teeth touching belt Now >12 of 18 teeth touching belt Added Plastic Idler pulley on shoulder bolt

7/7/2015Joel Graber27 Servo powered Gripper with 4 bar Bottom bar from servo to hinge pin does not move Good example of over-center for high-holding power. (photo credit, David Kwast) Bars are different lengths, Large input angle change => small output angle change

Servos vs Motors Motors get “speed” input Servos get “desired angle” input Servos are never used for wheels Servos have limited movement range – So less opportunity for gearing Normally used for grippers Can be used as triggers for strong spring powered mechanism – (eg crossbow) 7/7/2015Joel Graber28

What to do when the Arm is too heavy to lift Counter-weights – Gripper motor as counter weight – Pennies in PET bottle now allowed, Spring assist – Metal door spring – Elastic spring (bungee, rubber band, innertube) – Simple arm end vs wheel wrap – Cardiod cam or other calculated cam wrap 7/7/201529Joel Graber

Springs Door spring Bungee cord Rubber bands Clothespin torsion springs Deformation of any C-kit item – Bicycle tire inner tube rubber 7/7/2015Joel Graber30

String Drum and Arm wheel Large diameter arm wheel directly mounted to arm String winds and unwinds directly on extension of motor shaft Bungee spring assist Eyebolts for string guides 7/7/2015Joel Graber31

Electric summary Only soldering needed is to motors and sensors Use heat-shrink tubing to keep electricity from leaking out…. Strain relief on wires Limit switches Angle sensors 7/7/201532Joel Graber

Dallas BEST 2014 Rookie Build Session 33 Motor Wire Strain relief use a Zip-tie

Photos of BEST Robots Compliance/Judging Photos from TEXAS BEST 2014 Regional These were all winners from hub competitions. Chosen to illustrate various mechanisms 7/7/201534Joel Graber

7/7/201535Joel Graber Sm Motor operated claw, with just ¼ rotation, shaft coupled to Igus rod ½” Al rod for arm body PVC slider, with counter weights Rubber wrapped wheels for traction on ramps

Heat bent PVC slider Dual servo operated gripper Braced Arm frame with piano wire pushrods PVC pipe arm with wire management 7/7/201536Joel Graber

Plastic half Gear for arm lift Turntable gives the Arm a second degree of freedom Battery holder 7/7/201537Joel Graber

Compound gears in wood and plastic (photos: D Kwast) Note Larger teeth are better, use a real tooth profile from woodgears.ca or some CAD program 7/7/201538Joel Graber Simple arm-tail spring assist No bearing just hole in PVC! IGUS rod-end bearings with Igus axle PVC axle spacer Torque goes Gear to gear Not rely on axle

Last year belt and pulley for string drum lift Igus shaft and bearings Igus linear sliders for fork lift Dual servo operated gripper Of some kind Small notched wheels Axle hubs 7/7/201539Joel Graber

Bungee spring arm assist Curved arm of laminated wood No gripper, just hooks Arm lifted by Compound gear train Heat bent plastic sheet battery holder 7/7/201540Joel Graber

PVC arm frame Brace Dual string drum lift Oversized PVC fittings used as linear sliders on PVC pipe Counter weight holders for pennies to move Center of Gravity closer to wheels 7/7/201541Joel Graber

Eyebolt as string pulley for 2x force Unfolding arm 4 wheel drive with plastic gears (very unusual) 7/7/201542Joel Graber

Heat bent PVC as string guide Igus wire management chain Electric wire as string Hole saw plug string drum sides Penny counter weights Skate wheel caster 7/7/201543Joel Graber

7/7/201544Joel Graber Dave’s Cardboard robot

Common Mech pitfalls Picking up random stuff from shop and using it, instead of supplied materials. Overly complicated designs Ignoring Friction: – esp hard school floor vs soft carpet field Underestimating forces, bending moment of long arm on tiny bearing Ideas >> Craftsmanship 7/7/2015Joel Graber45

Summary Key Takeaways Review available materials and their properties before you start Power = Force * Speed : transformations L/S motors and servos are different Iterate early and often Prototype in cardboard & hot glue & last-years wheels – no hot glue on final robot, prone to self-disassembly in a hot car, plus not on the materials list – no last-years parts on final robot!, – new motor hubs required every year Some standard stuff can be started while design goes on: wheels, hubs, shaft connectors, casters/slider for driving games, pulleys, woven nets, braided line, motor leads soldered, battery holders, servo mounts 7/7/2015Joel Graber46

7/7/2015Joel Graber47

7/7/2015Joel Graber48