How Weed Eaters Work (at 62,000 FRAMES PER SECOND) – Smarter Every Day 236

published on July 9, 2020

Hey, it's me, DestinWelcome back toSmarter Every DayIt's time for theWeed Eater episodeAnd the way– I wantedto shut the doorThe way you can tellthat I've staged all thisis that this Weed Eater'sgoing to crank up immediatelyBut here's the deal

When it comes tooperating a Weed Eater,I have a mental model in my headof how the Weed Eater worksLike, as it goes faster,it slings out these linesin a disk, right?But is the disklike a solid linepointing straight outfrom the Weed Eater head?

Or I guess you couldcall it the trimmer headOr is it more likea lagging wave?I don't knowCheck this outLet's lookSo if I'm going to weed eatthis whole spot right here,

I rev up the Weed EaterBut when I don't revup the Weed Eater,you can see thatthe line is laggingIt's all curled upSo at some point inthere, it straightens outThen I can go in

I can trimAnd for some reason,I feel likeI should trimfrom right to leftI don't know why, but itjust feels like that'ssomething I should doLet's go over here to this

Watch thisIf I come down,should I plunge?You see that lays the grassdown in a certain way,but if I go likethis, it doesn't?I don't knowMy point is there'sa lot of physics

In how Weed Eaters workAnd there's thesequantitative thingsthat we should beable to measurewith a high-speed cameraBut there's thesequalitative thingsthat you just know if you spendtime running a Weed Eater

So today on SmarterEvery Day, I wantto take that internal mentalmodel of how Weed Eaters workthat I've developedover years and yearsof running Weed EatersAnd I want to test itwith a high-speed camerato see if we can understandthe physics

Of howa Weed Eater worksLet's go get"Smarter Every Day"What up?TRENT: What's up, man?DESTIN: Trent isgoing to be the trigger manon the slow-mo camera for us

So I'm going to berunning the Weed EaterAnd I'm going to get thatWeed Eater head positionedover this X right hereAnd we're going to usethis Phantom v2511We'll record it at about I'dsay 12,000 frames per secondAnd then we're going to see ifthe Weed Eater line slings out

Or, more accurately,see how it slings outBecause if you think aboutit, as the line is whippingthrough the air, youhave aerodynamic dragacting on the Weed Eater lineBut you also have theangular accelerationslinging the line out

So you've got thisbalance of forcesThat being said,the question is,does the line evertruly get straight?Because in my head, I'moperating with a diskwith straight lines out of it12,000 frames per second

OK, ready on trigger?TRENT: YupDESTIN: Here we goHa!Ready?TRENT: Yup

DESTIN:It's a simple test,but it should show us exactlyhow that straightens outAll right, so as wespeed faster and faster,you can see that theline is lagging behind,probably due to that dragthat we talked aboutBut there's also still a littlecurl at the end of the line,

Probably because it remembersbeing wrapped around a spoolMy question is, if wemake the line even longer,will this drag beeven more pronounced?Meaning, would it lagbehind even further?There's only oneway to find outWe got to test it

If we were to remove thisguard– don't do this at home,all that stuff–I think what wouldhappen is we wouldsee that theaerodynamics would startto win, like the dragon the line, right?Here we go

Let's do thisIt's hot in this helmetIt's going to hit my kneeSo I'm learningall kinds of stuffLike, the torquedemand on the motoris a function of the lengthof the line

And theaerodynamic dragSo for example, while he'ssaving that high-speed file,listen to thisIt doesn't rev all the way upRight?But if I cut thatline off

I never thought about thatHuhTRENT: This looks so AlabamaDESTIN:That's a good thingIt's like The StigThis is the Alabamaversion of The Stig

Roll tide, babySo once the Weed Eater linegets to a certain length,the aerodynamic dragis just too much,and the whole systemlags significantlyBut Weed Eaterdesigners were clever,and they integrated areally interesting tool

To make sure the lineboth stays balancedand at the optimum lengthThere's a featurein a Weed Eaterwhere you can tap thehead down on the groundYou hit the button at the end,and it will release more linefrom both sides of the spool

There's also an integratedblade in the guard itselfSo when the linegets long enough,it will trim the weed eaterline to the right sizeBut I've always wonderedhow that cut takes placeThis is an older WeedEater I've had for a whileAnd I don't expect itto make a clean-cut

But I want to use theslow-mo camera hereAnd Trent was pretty smartand came up with a mirrorto bounce light up inthere so we can see itSo let's see what exactlyhappens when we bump the lineand get moreWe'll see what thatcut looks like

TRENT: Good?DESTIN: Yeah, got itThere's so much to seeSo it's not a single cutlike I've always thoughtIt's like a continuouswhipping until it pulverizes itinto the right length

The torque on theengine is a functionof the length of the lineThe line is determined by theposition of the knife bladeThe balance is determinedby both sides of the linebeing equalIt is time to cut grass

Let's go cut grassTRENT: Ready?DESTIN: YupOK, I've got a theory that thereare different types of grassesthat behave differentlyLike, that was a blade of grass,and it kind of de-laminated

When it started gettinghit by the thing,it started ripping apartBut if we go over hereto something like thisthat's more of astalk-y type of grass–I don't know ifyou can see thisI wonder what's going tohappen there,

Because it's goingto rip differentlySo let's see if we canget a slow-mo of thatTRENT: Ready?DESTIN: Look at thisYou've got a stobThat's a grounding rod

So let's replicate thatWe've got a metal stobright here in the ground,and it's hammered inI've noticed thatwhen I'm weed eatingand I hit something like that,it'll pull my Weed Eater inOK, here we go

I always thought thathitting an object like thiswould pull the Weed Eaterdirectly towards the steel rodBut if you look closely,you can see thatit's a littledifferent than thatThe line is hittingthe top-right sideof the steel rod

And you can tell this by theway the line wraps around itIt almost makes itlook like a pulleyIf you were to draw a line inthe direction of that force,you can see that that's thedirection the trimmer headgets pulledJust play it forward,and you can see

That it kind offollows that lineSo it's not being pulleddirectly in like I thoughtIt seems to be reactingto the force that'sbeing applied to that rodAll this happensso incredibly fastthat I never thought aboutwhat was actually happening

OK, the next thing we'regoing to talk aboutis what happens when a WeedEater goes up next to a fenceOver here, a long timeago I had an ideaI wanted to create alittle gourd gardenAnd so I put this wirefencing, if you can see thatI put this wire fencing upnext to this wooden fence

Now, over time for somereason I came out here,and I'd weed eat this thingAnd it would breakmy Weed Eater lineAnd I got tired of thatSo I just quit Weed Eating itSo now we have big 20-foottrees and stuff like that

So to try to understandwhy I got frustratedand quit weed eatingthat stuff,we have set up a WeedEater obstacle courseWe've got chain-link fence hereWe've got what I call"hog wire" here,which is maybenot quite hog wire

But it's a pretty stoutwire, but it's still notquite as strong asthe chain-link fenceAnd then we've gotthis other oneIt's a smallerdiameter fencing hereSo the idea is with thestob, the Weed Eater linewould rotate aroundthat stob, right?

And it would act like a pulleyIf we have a smaller diameterhere, does it do that?Or is the minimum bendradius a lot smaller,and will it just cut it?OK, it feels more like scienceif we take some measurementsSo looks like about 0110,0112 an inch on the chain link

And let's look at theWeed Eater line itselfLooks like we're around0095 of an inchYeah, it definitelypulls it to the sideThe question iswhat is the interactionof that Weed Eater lineto the fencing look like?Aw, that's awesome!

That's awesomeSo it wrapped around itAnd at times, itdoesn't break itAnd at other times, it doesOh, what happened there?Oh

TRENT: DESTIN: OK, if the WeedEater line wraps 360 degreesaround the fencing, then it–is it a tension break?It rips itTRENT: Wow

DESTIN: Oh!OK, coolSo it's like a spaghettificationof the Weed Eater lineIt wraps around the fenceAnd then if it goes 360, ithas to unwind the whole thingAnd sometimes it'seasier just to break

I can't tell if it's a tensionbreak or a sheer breakBecause the chain-linkfence is on a diagonal,it looks like as the WeedEater line comes inand hits the fence,it funnels it to the cornerAnd because there's anotherwire going through the corner,it's like a pinch point

I bet if we go to thesmaller diameters–yeah, if we go to thesmaller diameter wires,it's going to have asmaller radius of curvatureit has to bend aroundMm MmInteresting

We need to move onto the next oneWhat I'm calling hogwire is about 0085It definitely grabbed moreAnd you can see that thereare some tension issues thereIt's trying to pullThe brake is verydifferent than I thought

It's a tension break, atleast on this, because itseems like it's wrappingAnd it's pulling so fastIt's unwrapping itso fast, like a whipAnd it's a tension breakSo there you go

We've learned somethingIf it goes around360 degrees, then ithas a really toughtime recoveringAlso, this has got to bedifferent with a square lineor a triangular ora polygon-type lineWe're going to do anothervideo following up

On this with differenttypes of Weed Eater lineOK, here we go, timefor the small stuffThis is 0060 of an inchThis is smaller thanthe Weed Eater lineLet's do itTRENT: Whoa!

DESTIN: Yeah, that's–TRENT: That was scaryDESTIN: That's scary,but that's– that's whatit's like to weed eat– that'swhy you always sneak up nextto the fence, because you'reworried that it's going to grabyour Weed Eater and go

OK, it broke at thewelds, which makes sensebecause when youweld wire like that,there's a heat-affectedzone on that wireSo right there, I wouldexpect right near the weldto be the weakestpart of the wireThis didn't break Wow

This episode ofSmarter Every Dayis sponsored by Raycon earbudsI'm going to show youmy everyday carry stuffEvery morning, I wake up,I get my multi tool,my phone, my wallet,and I get the Raycons

I throw them all in my pocket,and then I go start my dayBut the Raycons are themost interesting thing to mebecause they havethis little case–sorry, I just gotsome grass in thereThey've got thislittle bitty casethat charges these earbuds

And they pair seamlesslywith the phoneIt's really impressiveThese are called theE25s, the Everyday E25sAnd what's so coolabout them is youget six hours ofplay time on these,and they don'tcost a lot at all

These things startout at half the priceof the other toppremium audio brandsAnd they sound just as awesomeI like them so much–these are mine– I'vehad these for months–that I reached outand I purchased these

This is the E55 PerformerI paid for this with mymoney because I wanted them,and I wanted them in blueThis is what I wassuper excited aboutI just open these thingsI have not tried them yet, butthese fit really, really good

In the ears;check this outIt's pretty coolSo they just go right there–boomYou can run in themI used them to weed eat, mowthe yard, things of that nature

They're fantasticI haven't tried these E55s yet,but I certainly love the E25sNow, these they sent me becauseI'm doing this ad, right?Like, I didn't pay for theseI did pay for these becauseI like these so muchSo if you want tocheck this out,

Go to buyrayconcom/smarter,and you can get 15% offYou will like themYou will enjoy themMost importantly, ifyou lose these things,that's not the end of the worldThey're priced right inthat right sweet spotYou get four chargesout of the little pill

You get six hours on this thingYou're going to dig themThat's itBuyrayconcom/smarter, 15% offI hope you enjoyed this videoI've heard peoplemy entire life say,

Oh, triangular WeedEater line is bestSquare Weed Eater line is bestTwisted square is bestRound is bestWe're going to solve thatWe're going to test themwith empirical tests

So we're going to have dataWe're going toanswer the question,"What is the bestWeed Eater line?"If you would liketo see that video,please feel free to subscribeto Smarter Every Dayby clicking the littleSubscribe button,

Maybe even the bellIf not, that's no big dealI hope you enjoy your summerout weed eating the yardI know I am lookingforward to it myselfGo get some vitamin DAnyway, that's it

I'm DestinYou get "Smarter Every Day"Thanks for subscribing,maybe, if you feellike this video earned itIf not, that's coolHave a good one Bye

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