The force vectors on a skateboard during an Ollie

http://www.wired.com/2014/10/skateboard-physics-empzeal/

by aatish • 12 years ago

194 52 12 years ago

Terr_2• 12 years ago

It looks like the skater drags his shoes against the "lip" of the skateboard to get a bit more "forward" direction on takeoff, pulling it upwards.

rosser2• 12 years ago

We are dragging the shoe on our forward foot, but it's against the "grip tape" (made from crushed glass in a bed of adhesive). The force of friction from the shoe sliding forward against the grip tape is, in conjunction with the upward force from striking the tail of the board against the ground, sufficient to lift the board. Coordinating those two motions is the essence of an ollie.

chrisdone3• 12 years ago

Ollie is the hardest thing to learn in skateboarding. It took me and my friends a long time. I think it's hard to explain it, so it's hard to teach.

It's rather that the initial smack or pop of the tail against the floor makes the board fly upward, which you can reproduce by just by stamping on the tail of your board. That was my first insight.

You can do a standing Ollie with one foot: stamp it and as the board starts going up you shove your same foot to the right to stabilize it. After mastering that, a two-foot Ollie was just a matter of practice. Also, the longer you delay putting any downward force in the nose, the more air you get. I feel like I should make a video of a standing single foot Ollie, as two feet complicate demonstration, I think.

The moving forward of the foot isn't for adding more forward velocity, a standing Ollie can get really high and land in the same place. A moving Ollie relies on your existing velocity, which should be pretty high.

I've not skated for about 10 years, but I got a board recently to see if I still had it. Ollie'ing is like riding a bike, never forget how to do it. :)

chrissnell• 12 years ago

I've not skated for about 10 years, but I got a board recently to see if I still had it. Ollie'ing is like riding a bike, never forget how to do it. :)

It's tough for me. I skated nearly every day of high school and not much since then. I got on a board a few months back and it was like starting all over again. The biggest difference that I noticed was my diminishing flexibility. I need to start managing that--my wife, a physical therapist, says that lack of flexibility in our 30's and 40's is highly correlated with likelihood of falls when we are elderly.

jere2• 12 years ago

It's rather that the initial smack or pop of the tail against the floor makes the board fly upward, which you can reproduce by just by stamping on the tail of your board. That was my first insight.

I see this repeated over and over. Maybe I'm misinterpreting your comment, thought I've definitely seen it elsewhere such as this comment on the article:

It actually looks like he "bounces" the board while starting the ollie, which provides a portion of the initial upwards velocity of the board.

Think about that for a moment. This is patently absurd. It's like trying to get several feet of air by crouching down and hitting the ground with a hammer. The collision is too elastic.

I think the confusion might arise because a really strong smack of the ground by the tail coincides with more torque (torque, right?). Of course, you can easily ollie if your tail hangs over nothing at all; it's probably even easier because you can rotate further.

IMHO, Terr's guess is exactly right. You get all the lift from pushing down the nose / dragging across the grip tape.

ap222132• 12 years ago

I wouldn't say it's the hardest, but it's definitely the first hard step.

I learned to ollie in the summer of 1987. It had taken me and my brother about 6 months to figure it out. The hardest part was training our brains to be ok with it. Once we landed a few, it was then fairly simple. But, it was the landing that was most difficult. We intuitively understood the motion and forces required, but we resisted letting our back foot follow through.

By 1989, we were able to do bike racks, picnic tables (with appropriate ramp angle), garbage cans. And, we eventually figured out the kick flip, which was the second hardest trick to learn (at first).

Now, the 360 flip to handrail grind - that's a freaking hard trick that requires some guts to let oneself do. And, it's one of those tricks that requires a good video camera nearby to establish proof.

brc• 12 years ago

Big moment in my childhood was learning to 'pop an ollie'. From that moment on, you could separate yourself from others with these seemingly impossible standing jumps up kerbs and over obstacles. I didn't ever really get much higher than maybe a foot on my best day, but it was great fun.

Now I feel like finding a board just to see if I can. Sadly my Powell Peralta was lost with my Lego in some parental clean out while I was out being an adult that had flown the nest. I'd gladly trade my school photos and stupid artwork that was saved to get those back again.

bronson• 12 years ago

The "a-ha" moment for me was concentrating on driving my rear foot into the ground.

No matter how you jump or drag your front foot, if you don't get a good solid "pop" on the tail, nothing happens. Felt weird at first but now it seems like it couldn't be any other way.

(where "now" is 10 years ago, when I last ollied anything... wtf)

agumonkey• 12 years ago

It helps but it's not necessary. It's a game of shifting centers of rotation.[1]

    Kick the backend :: upward tilted lift, center : ~back wheels.
    Quickly slow the frontend :: upward tilted lift, center : ~front wheels.

[1] it requires suppleness in choreography, that's why any kid can do it, they're swift; the window of execution for both steps are very tiny. And they ask you to uncouple your mind, your feet and your center of gravity. Mind altering leap of faith it is.

swimfar• 12 years ago

I always thought this was the most logical explanation. Look at how high people can ollie,[1]. This wouldn't be possible if it they were just changing the axis of rotation. And this video here shows the skaters clearly pulling the board up with the grip tape/front lip [2]. Sliding your foot along the board is one of the basic steps for olling.

[1] http://www.youtube.com/watch?v=IYE-ZaXbzUg

[2] http://www.youtube.com/watch?v=339k4XEvbxY

fedlarm• 12 years ago

Yes the Griptape is an essential part to make high ollies consistently. However ollie's are possible to do without griptape as well. Just a lot harder because you'll have a lot less control.

The harder you slam down the tail of the board the more friction you get, the easier it is to pull the board up/forward.

lbotos• 12 years ago

If you like this and you haven't seen 1000fps flatland tricks:

https://www.youtube.com/watch?v=aHrn3-Cb3iM

iaw2• 12 years ago

I hadn't seen that. It really emphasizes how much precision of timing/movement is required in order to pull off a trick.

weaksauce• 12 years ago

I was a decent skateboarder in my day but these tricks are an order of magnitude harder than anything that was happening in my day/era... the exception was rodney mullen. he was the only pro doing anything like that

cobalt• 12 years ago

Well Rodney Mullen invented almost all of the tricks. (Including the more famous ones like the kickflip and such)

lloeki• 12 years ago

I really dig what Killian Martin is doing in that regard: pushing limits, applied to an artsy end.

[0] https://www.youtube.com/watch?v=D_h-7Kp87OE

[1] https://www.youtube.com/watch?v=cbSbbY5ibas

aboodman• 12 years ago

Also: http://vimeo.com/1340684

adwf2• 12 years ago

I'm less impressed by the skateboarding tricks and more impressed by the physics software that can derive all this from a video.

frozenport• 12 years ago

Well tracking software has been around for a while. I did something like this for a highschool project...

adwf2• 12 years ago

I guess it's just something I'd never seen before, impressive at first sight! I did all my physics quite a few years ago and don't remember video analysis like this, although I guess it wasn't really my focus anyway.

iaw2• 12 years ago

The simple Ollie in that video is no where near as impressive as the tricks performed in the video lbotos posted (top comment currently). Unfortunately, I get the feeling the tracking software would have a hard time with any component of movement that isn't coplanar (including rotation).

ap222132• 12 years ago

Skateboarding is an incredibly fun sport. You should give it a try.

Too2• 12 years ago

There's no advanced physics software required to get the data in the video, he's just plotting the second derivative of a line he got by tracing the center of the wheel. F is proportional to a :)

ivan_ah• 12 years ago

I really like the overlay of physics information in the video. It is so much easier to explain to students what acceleration is by showing it rather than asking students to imagine "the second derivative of the position function r(t)=(x(t),y(t))."

Check out the software they used: http://www.cabrillo.edu/~dbrown/tracker/

subdane• 12 years ago

I never got any good ollies in high school. Watching the vids and reading the article I think I realized something I never understood. It looks like most of the skater's upward body acceleration is coming from using the the _left_ leg, with the right foot going along for the ride (and smacking the tail down). I always tried to get the major jumping lift from my right leg, while also somehow smacking the tail at the same time. I think I've always had it backwards!

snowwrestler• 12 years ago

The highest ollies come from jumping with both legs, and using the ankle of the foot on the tail (right if you're regular-footed) to flick the tail down and pop the board.

It's basically a two-foot jump; the hard part is getting the board to stay with your feet.

Too2• 12 years ago

Jumping on a bike is also basically a two-foot jump, where you pull the whole bike up after yourself using the handlebars. There is no special "pull up the front first and then push forward" as many people believe. The initial jerk is just to get the handle bars above the COG so that you can actually lift the bike from there and to put your pedals above the balance point of the rear wheel so you can push down hard for the actual jump. This might seem strange at first but when you think of it, apart from the legs what parts of the body have enough force to jump yourself that high, it's not like you can magically jump higher just because you are standing on some weird contraption.

On a bike you do get some help from preloading the tyres to give you a bit of bounce but that's minor compared to the rest of the movement.

Animats• 12 years ago

The motion capture shown is kind of limited. The wheels are tracked, but not the CG of the rider. Also, the video doesn't show the beginning of the ollie. It looks like, in this one, the rider did this entirely by loading up the springs in the trucks to get a bounce, rather than dragging the tail of the board.

It's a good physical simulation problem. Now that Gazebo has a real physics engine (by Mike Sherman from Stanford) rather than ones from video games, it should be possible to do an ollie in a robot simulation. (The game-type physics engines use an impulse/constraint model for contacts, which is unrealistic when you have a collision followed by sliding.)

anonfunction• 12 years ago

by loading up the springs in the trucks to get a bounce

There are no springs in skateboard trucks. The force comes from pushing down on the tail and then shifting your front foot up the nose.

seestheday2• 12 years ago

There are bushings which will provide a small amount of spring, but your general points stands that the force comes from pushing down on the tail and shifting the front foot up to the nose to pull the skateboard up.

aatish• 12 years ago

No, it doesn't make sense to track the center of mass of the skateboarder here. If you're interested specifically in the forces on skateboard, you want to track the center of mass on the skateboard. If you include the skateboarder in your system and track the new modified center of mass, you will only see the effect of gravity, being the only remaining external force.

seestheday2• 12 years ago

Tracking the centre of mass of the skateboarder would give you an idea of how to get additional height on your ollie. Essentially sucking up your legs, bending at the waist and throwing your arms down will allow you to clear higher obstacles.

tjradcliffe• 12 years ago

You don't actually need any fancy software to see what's going on if you've mastered the fine art of free body diagrams: http://www.tjradcliffe.com/?p=1374 (not related to skateboards, but those damned wobbly suitcases).

And the advantage of simple free body diagrams is they are amenable to relatively simple models, frequently involving simple harmonic motion: http://www.tjradcliffe.com/?p=1410

These are teachable skills, and while it's great we have software to help us out, I'm a sufficiently aged crustacean to see the value in learning to do these sorts of analyses formally, by observation and inference.

thret3• 12 years ago

For anyone trying to learn how to do an ollie for the first time, the one thing that really helped me was this: do it on grass. I spent ages on concrete, and it is a lot harder. On grass the board doesn't roll and you don't get hurt if you fall.

A bit like learning to walk on your hands - start in a shallow pool. Once you get comfortable with the motion translating it to a different surface is not that hard.

mbenjaminsmith• 12 years ago

Yeah, that's how I did it. Grass is helpful until you can get the board to come up close to level and land on it.

For some reason it took me much longer to learn how to drop in on a ramp. I built an 8-foot ramp in high school (no vertical) and it took me ages (weeks, IIRC) to drop in without immediately planting a foot and running or falling down the ramp.

When I finally nailed it I was so happy. Damn, I miss skateboarding.

thret3• 12 years ago

I remember the first time I dropped in too. It is another one of those things where if you don't commit all the way, you fail. Once you get it you have it for life. I think having my friends get it first helped me with that one!

I'm impressed you built a ramp! Luckily there was a nice new outdoor skateboard park near my friend's house, we didn't have to build anything :)

ratsimihah• 12 years ago

Doesn't grass absorb most of the pop, though?

thret3• 12 years ago

You may be thinking of longer grass? It is just important that the board doesn't move forwards or backwards while you are practicing.

The force vectors on a skateboard during an Ollie

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