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The force vectors on a skateboard during an Ollie

194 pointsby aatishover 10 years ago

8 comments

lbotosover 10 years ago
If you like this and you haven&#x27;t seen 1000fps flatland tricks:<p><a href="https://www.youtube.com/watch?v=aHrn3-Cb3iM" rel="nofollow">https:&#x2F;&#x2F;www.youtube.com&#x2F;watch?v=aHrn3-Cb3iM</a>
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ivan_ahover 10 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 <i>showing</i> it rather than asking students to imagine &quot;the second derivative of the position function r(t)=(x(t),y(t)).&quot;<p>Check out the software they used: <a href="http://www.cabrillo.edu/~dbrown/tracker/" rel="nofollow">http:&#x2F;&#x2F;www.cabrillo.edu&#x2F;~dbrown&#x2F;tracker&#x2F;</a>
thretover 10 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&#x27;t roll and you don&#x27;t get hurt if you fall.<p>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.
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adwfover 10 years ago
I&#x27;m less impressed by the skateboarding tricks and more impressed by the physics software that can derive all this from a video.
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subdaneover 10 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&#x27;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&#x27;ve always had it backwards!
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tjradcliffeover 10 years ago
You don&#x27;t actually need any fancy software to see what&#x27;s going on if you&#x27;ve mastered the fine art of free body diagrams: <a href="http://www.tjradcliffe.com/?p=1374" rel="nofollow">http:&#x2F;&#x2F;www.tjradcliffe.com&#x2F;?p=1374</a> (not related to skateboards, but those damned wobbly suitcases).<p>And the advantage of simple free body diagrams is they are amenable to relatively simple models, frequently involving simple harmonic motion: <a href="http://www.tjradcliffe.com/?p=1410" rel="nofollow">http:&#x2F;&#x2F;www.tjradcliffe.com&#x2F;?p=1410</a><p>These are teachable skills, and while it&#x27;s great we have software to help us out, I&#x27;m a sufficiently aged crustacean to see the value in learning to do these sorts of analyses formally, by observation and inference.
Terr_over 10 years ago
It looks like the skater drags his shoes against the &quot;lip&quot; of the skateboard to get a bit more &quot;forward&quot; direction on takeoff, pulling it upwards.
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Animatsover 10 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&#x27;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.<p>It&#x27;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&#x2F;constraint model for contacts, which is unrealistic when you have a collision followed by sliding.)
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