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# 3D Sprinting

(title by Flying Toaster) "He's cleared the loop, now he's almost horizontal on the hairpin turn!"
 (+3, -1) [vote for, against]

I saw a video of somebody running a loop shaped track, that's where he flipped a full 360 degrees and came out the other end. If you're running fast enough, you can, for a second seem to defy gravity.

So take this concept a step further and have a running track shaped like a roller coaster. In addition to loops, you'd have sharp banks where the runner would be almost horizontal.

If you weren't going fast enough, you'd simply fall off the track.

This would be a no brainer great addition to those obstacle course shows that are pretty popular these days.

And if the ratings drop? Put the whole thing over an alligator pit for the next season.

And kudos to Bigsleep even though his anno makes no sense any more since the title change.

 — doctorremulac3, Aug 12 2015

Runner doing a loop de loop. https://www.youtube...watch?v=OTcdutIcEJ4
Fast forward to 2:20 [doctorremulac3, Aug 12 2015]

The easy way with roller skates. https://www.youtube...watch?v=kBo0Tsv5v0s
Of course a running course would need tighter curves. [doctorremulac3, Aug 13 2015]

And jumps; with the approach and landing ramps angled for an appropriate approach speed, you should be able to clear an impressive distance.
 — pocmloc, Aug 12 2015

 The problem is that the animal stride is not well equipped for running on non-horizontal surfaces. Every instance I've seen of a runner "looping" is essentially a running backflip inside the loop.

The reason is that the human stride consists of about 90% upward push and about 10% forward push (numbers pulled out of the air, but it's something like that). A runner in a forward leaning sprint can do significantly better, but still not great. This works fine if you've got a force (gravity) countering that upward push, but not so good if you don't. Since so much more of the force is upward than forward, the human cannot physically run fast enough to treat a banked surface as a straight one for any significant degree of bank for any significant length of time.
 — MechE, Aug 12 2015

 //the human cannot physically run fast enough to treat a banked surface as a straight one for any significant degree of bank for any significant length of time.//

 Who said anything about "significant length of time"? Ever seen anybody do parkour off of a wall? You run up to it, run on the wall horizontally for about 2 seconds then obviously return to the vertical.

As far as your incorrect contention that a runner is just doing a backflip when he runs a loop de loop, see link.
 — doctorremulac3, Aug 12 2015

I stand by my statement. He's dependent on the push off the far wall to make contact with the near, he never actually takes a step along the wall as such.
 — MechE, Aug 12 2015

Except that he does. Watch the video.
 — doctorremulac3, Aug 12 2015

 (marked-for-tagline)

" numbers pulled out of the air, but it's something like that "
 — normzone, Aug 12 2015

So what are you saying, you can't have a course that features the loop for starters and has less challenging parts based on the loop as well such as a sharp hairpin turn where he doesn't go fully inverted but merely goes horizontal for a second?
 — doctorremulac3, Aug 12 2015

Simple loops are for wimps. What's needed is a runners' wall of death.
 — MaxwellBuchanan, Aug 12 2015

 //Except that he does. Watch the video.//

 I did. One foot on the front wall, countering his forward momentum. One foot on the top, countering the upward momentum. One foot on the back wall, countering the push off the front. Landing. And he has to catch himself from falling on the landing. He's not running around the loop, he's using the loop to control a flip off the front ramp.

Once again, what I mean very specifically, is that unlike a rolling vehicle, his speed is not, and cannot be, sufficient to hold him to the loop.
 — MechE, Aug 13 2015

 //Hold him in the loop//? What on Earth are you talking about?

 The guy ran through a loop. Idea is for a track that features these loops and simpler, less hard to traverse versions of this loop such as horizontal hairpin turns similar to a roller coaster. Traversing these hairpin turns would be similar to a parkour runner running up and down a vertical wall. They would not be "held in the loop" or remain horizontal for any "significant length of time" so I'm not sure why you keep referring to these concepts.

If you're still not getting it, I don't know what to tell you.
 — doctorremulac3, Aug 13 2015

 //his speed is not, and cannot be, sufficient to hold him to the loop.//

 I agree with [MechE]'s analysis of the video, but to be honest that's not the point. The guy did effectively run around the loop. The forces he was applying were broadly similar in type to the forces he'd be applying if he ran level, but not quite. There is an element of back-flippiness to it.

 The real test would be whether he could complete two or more loops - sustained looping. I'm not convinced that he couldn't.

 The other relevant question is: what speed would the runner need in order to maintain, say, 1.5G of centrifugal force? (Why 1.5 and not 1? Because 1G would leave him with net zero G at the top of the loop, and he wouldn't get any traction. With 1.5G centrifugal, he has 0.5G of force between him and the top of the loop, which is enough to maintain traction.)

 Well, let's assume that the loop is 3m in diameter (1.5m radius), which seems a reasonable minimum. Assume also that the runner's centre of mass is 1m from his feet (that's not quite right, but it will do). So the radius around which his centre of mass goes is 0.5m.

It turns out that a speed of about 5.5m/s, or around 12mph, will be enough to provide 1.5G of centrifugal force. Of course, he's doing some of that vertically, which will be strenuous, but it's not insanely impossible.
 — MaxwellBuchanan, Aug 13 2015

 Right. Not insanely impossible, but insanely difficult, which is the point.

 However you break down what is happening to get him through this loop, or through a near horizontal hairpin turn, you'd have to have a certain amount of speed and momentum to get you through the obstacles. Too slow, you fall off the track.

 Let's face it, running isn't all that exciting to watch, or to do for that matter. With this roller coaster track, if you don't run fast enough, you plummet off the track. In the case of the loop, you fall directly on your head, something that seldom happens in regular running races.

 All the aspects of a roller could be featured, including a sharp drop. If you've ever ran down a hill that's sharply angled down, you'll know that simply keeping on your feet is pretty hard to do. You've got to get going really fast to "catch a continuous fall" basically.

I'm seeing a lack of buns for this. Did I mention this would be much more dangerous than regular running tracks?
 — doctorremulac3, Aug 13 2015

[+] the vid of somebody actually doing it clinched it.
 — FlyingToaster, Aug 13 2015

 In that video I noticed that the guy's head was almost stationary. I think that was a large contributor to why it looks somewhat like a back flip. Of course making the radius more than the runner's height is going to make the required speed higher.

 Regarding the 1.5G recommendation: Like you said, that means that at the top of the loop there's 0.5G (great), but at the bottom there is 2.5G. When's the last time you tried to run carrying a pack that's 1.5 times your weight?

 Also check your calculations, it looks like (5m/s)^2/1.5G = (25m^2/s^2)/(14.7m/s^2) = radius of 1.7m, not 0.5m like you said.

 One solution to lower the Gs at the bottom of the loop might be a non-circular loop with a tighter radius at the top and gentler ramps into and out of the loop.

 Another option might be a loop with a radius of about 2.5 meters with a gymnastics bar (or similar) through the center of the loop. The runner would reach up and grab the bar as they enter the loop. This would allow them to more efficiently swing their weight up and around rather than requiring all the centripetal acceleration to come from their legs. It would of course also allow doing the loop with less than 1G. It looks like raising the center of mass 3 m in this case will use up 5.4m/s of the original velocity, but assuming a reasonable athlete can manage 7 or maybe 8 m/s entering the loop, they should have no problem getting over the top. I'm not sure if they could maintain enough speed to avoid negative Gs a the top, so that may rule out a trapeze for larger diameter loops.

Of course the race course should include several different types of loops of various size/shape.
 — scad mientist, Aug 13 2015

Added link to some info on similar-ish racing types. Parkour looks fun, but that tends to not focus on timed racing. I can see why since there could probably be a lot of injuries on concrete obstacles if the focus was on speed rather than form. I could see a race like this idea as having a niche if the obstacles are designed to in general become less dangerous at higher speeds. A wipe- out would generally result in sliding off the track into the pads (or alligator pit). On a well designed endurance course I could see a that a winning strategy would involve pacing yourself on the less technical sections so that you had enough energy left for the final loop or 90 deg hairpin turn.
 — scad mientist, Aug 13 2015

 //result in sliding off the track into the pads (or alligator pit)//

 That would depend on how high you wanted your TV ratings.

 You know, another daunting obstacle would be a simple ramp at the and of a steep slope. Picture the track going down and then turning up into a 90 degree angle relative to the ramp. You hit that too softly you're essentially running full speed into a wall. You'll have to run like heck to keep perpendicular to the track as it angles up or Blammo!

I'm not capitalizing "blammo" to give it proper noun status, but to more accurately represent the sound you'd make hitting the ramp turned wall. All caps would be too much, hinting at a sustained booming sound where it would actually be more of a sharp attack followed by not much else, indicated by the capital B and followed by the lower case "lammo", perhaps representing bouncing, flailing limbs and such.
 — doctorremulac3, Aug 13 2015

I think the onomatopoeic word would be "Blap".
 — MaxwellBuchanan, Aug 13 2015

 "Bla-blap" perhaps if there was a bounce invloved. "Blap" implies a more gruesome outcome.

Anyway, see link for a guy doing it the easy way with roller skates. The running course would need tighter curves of course unless the guy could run 40 miles per hour.
 — doctorremulac3, Aug 13 2015

If there's a bounce, the sound is more "nuAAABlap...tmp."
 — MaxwellBuchanan, Aug 13 2015

 There's probably a voice-to-text algorithm that could be tweaked to give you pretty good onomatopoeic (my new word for the day) words. Just hold the mic up to the event and have it read out an approximation of how you'd spell it.

Might help answer age old questions like "How do you spell a raspberry?"
 — doctorremulac3, Aug 13 2015

 My problem is that you are describing it like a roller coaster track, and it doesn't work. You can do a backflip. You cannot run around a loop larger than the backflip you can do.

 You can do one or two steps up against a wall for your hairpin turn and then drop down to the ground underneath it. You cannot make a banked turn like a wheeled vehicle and end up upright on the same track you were running before. So everyone "falls off" the track, at most the challenge is can you start with enough horizontal momentum to reach the next platform.

 As a parkour course, sure. As a roller coaster like track, no.

 //what speed would the runner need in order to maintain, say, 1.5G of centrifugal force?//

 They can't. That's my point. A wheeled vehicle gets its forward momentum entirely through friction tangential to the wheel along the supporting surface. The normal force (that extra 0.5g) is required for friction to happen, but the component imparting motion is entirely tangential to the surface.

A running individual gets its forward momentum by pushing down and back sufficiently to overcome gravity. The force imparting motion has a tangential and perpendicular component. By definition, if they impart motion in the direction of travel, they are also imparting sufficient motion towards the center of the loop to overcome the inertial forces holding them against the loop, and they will lose contact with the loop without being able to make an additional stride in that direction. In the case of the video, he never makes an additional stride in that direction, he instead pushes off of the wall in each direction once, which is what gives it that element of backflipiness, because it was.
 — MechE, Aug 13 2015

 Big, you're absolutely right. Just running down a hill, while one might think would be easy since it's going down, is about the hardest thing you can do on your feet and when you hit that upturn, you've got some challenges.

 Just keeping upright overcoming the gravity and momentum pulling you down is hard enough, but when you slam into an upturn, well, do the math on that. I weigh 180+ pounds, I'm running downhill at around 20 miles per hour at least since I'm making huge strides and basically engaging in a controlled fall. Then I'm supposed to re-direct all that mass almost 90 degrees? How many pounds are my legs supposed to support for that split second? That sounds like a sporting event to me.

 //My problem is that you are describing it like a roller coaster track, and it doesn't work.//

 Mech, I'm pretty sure that's not your problem. I've described a track featuring a loop shown in a video that shows a guy traversing it, you say he can't traverse it, yes, he can, it's on video. I really don't know what to tell you. Just bone it and move on my friend. Let it go already.

By the way, speaking of running down hill, many years ago I had the genius idea of running down the side of a very large hill and when I lost it, made the bad decision to not just sit on my butt and slide the rest of the way. I kept on my feet and basically jackhammered every bone in my body. Messed up my hip socket and needed to walk on crutches for a couple of months. Somehow it completely got better, socket injuries can tend to be permanent, but I learned my lesson.
 — doctorremulac3, Aug 14 2015

Perhaps the video is fake. CGI track, rotary camera mount, convincing acting.
 — pocmloc, Aug 14 2015

 I did not say he cannot traverse that loop. I said he cannot run around that loop. They are two different things.

And a backflip is around your center of gravity taking into account your momentum. If you do it from a running, jumping start, it goes forward and up then back down as gravity dictates. That is what he is doing, but he's using pushes off the wall to control that momentum. He is not being supported by the wall the same way a vehicle in a loop is.
 — MechE, Aug 14 2015

 I'm with MechE - I've watched the video, and in the slow motion replay it's clear that the foot plant at the top of the loop is very gentle, and he's basically coasting at that point. Don't get me wrong, I think it's valid to claim it as a loop-de-loop - but the point is that you can't extend from that to a 'wall of death'. Because humans can't run all that fast, and don't have much in the way of down-force.

 //So what are you saying, you can't have a course that features the loop for starters and has less challenging parts based on the loop as well such as a sharp hairpin turn where he doesn't go fully inverted but merely goes horizontal for a second?//

 And I think the answer is that you could.

 But. Let's go back a moment.

 //the human cannot physically run fast enough to treat a banked surface as a straight one for any significant degree of bank for any significant length of time.//

Humans just don't have the downforce. Until...
we attach the rocket powered 'spoilers'!
 — Loris, Aug 14 2015

 //you can't extend from that to a 'wall of death'. Because humans can't run all that fast, and don't have much in the way of down-force.//

A simple calculation of centrifugal forces shows that an athletic human should be able to run around a fairly small vertical wall of death. It would actually be a lot easier than doing a loop, since they don't have to suddenly raise their centre of mass.
 — MaxwellBuchanan, Aug 14 2015

 // simple calculation of centrifugal forces shows that an athletic human should be able to run around a fairly small vertical wall of death.//

But you can't model a running human that way. Running is not continuous contact with the ground, it is a series of pulses pushing off the ground. As a result you have a mixture of extreme centripetal acceleration and none, as opposed to the average centripetal acceleration found when a wheeled vehicle attempts the stunt.
 — MechE, Aug 14 2015

 // A simple calculation of centrifugal forces shows that an athletic human should be able to run around a fairly small vertical wall of death. // Can you show that calculation?

 You'll need to make an assumption about what angle is possible. From personal experience I can pretty easily walk on a 4:12 (rise:run) pitched roof, and would probably have little trouble running crosswise on such a slope. On a 9:12 roof, it would be highly questionable. But lets say the surface was really gripping and somehow I could run without twisting my ankle. That requires 12/9 = 1.3G of centripetal force. That plus the force of gravity = sqrt (1.3^2 + 1) = 1.67G. (like running with a pack containing 2/3 your body weight on a surface sloping 37 degrees to the side. That's maybe on the edge of possible.

 To get 1.3G centripetal force, you could maybe be moving your center of mass at 4m/s in a radius of 1.2m. Assuming your feet are 1m below center of mass, they will be travelling 4ms*2.2/1.2 = 7.3m/s.

So it may be possible to run on a vertical wall of depth with a radius somewhere around 2.2m. Okay, so I did the calculations myself.
 — scad mientist, Aug 14 2015

 // But you can't model a running human that way. //

I don't see why not. A normal runner running on a flat surface is fighting gravity using a series of pulses. When running around a curve, they are fighting gravity plus inertia with a series of pulses. If you calculate the total acceleration, it becomes equivalent to running on a planet with stronger gravity or running while carrying a heavy load. That of course severely limits what is possible. With a wheeled vehicle it's easy to handle several Gs without seriously changing horsepower requirements whereas with running the upper G limit will be small and the runner will tire very quickly near that limit.
 — scad mientist, Aug 14 2015

 //you have a mixture of extreme centripetal acceleration and none//

 When you run, you are only applying a force against G while your foot is in contact with the ground.

 I'll grant you, running around a wall of death will be very demanding. But I don't see it as impossible.

 As a reductio ad absurdam, suppose we give a motorbike solid tyres. Clearly, it can still do the wall of death. Now we cut cross-wise grooves in the tyres, so that maybe 20% of the rim is missing (split over say 12 segments). The ride will be bumpy, and the rider may have to steer "up" a little to compensate for short intervals of griplessness, but I think it's still doable.

 So now we make the gaps in the tyre less numerous (and wider). I suspect that, if the rider could take the bumpiness, we could approach a situation roughly equivalent to human footsteps.

 Or, if you prefer, consider the trajectory of the runner while both feet are off the surface. He will start to drop in a half-parabola which lies in a plane tangential to the wall at that point. Since he is moving forward, he will continue to move closer to the in-curving wall as he falls, allowing him to place his next foot.

 And to compensate for the dropping between footfalls, he just has to run "uphill" somewhat. By doing this, he ensures that while his feet are off the walls, he will describe a full parabola (ie, upward and then downward); if he gets it right, his next footfall will happen when he has returned to his original height.

A running wall-of-death is definitely possible. Whether it exceeds the athletic ability of a fit human I am not sure, but I doubt it.
 — MaxwellBuchanan, Aug 14 2015

Back in the 80s before we covered it up permanently, we had a pool which featured a circular, sloping deep end that was roughly conical. The bank was about 45 degrees, and we enjoyed running circles around it as kids. It might have been about 9 feet deep at the bottom and thus about 18 feet in diameter. We leaned in maybe 25 degrees or so. Centripetal force is cool as a kid.
 — RayfordSteele, Aug 14 2015

That gives me another idea.
 — doctorremulac3, Aug 15 2015

Bravo!
 — MaxwellBuchanan, Aug 18 2015

 //3D sprinting.//

 Ladies and gentlemen, we have a last minute title change.

(Credit will be given where due)
 — doctorremulac3, Aug 18 2015

 We can't give any more credit for this idea but we're willing to say something nice about you at the end of the idea.

Fair enough?
 — doctorremulac3, Aug 18 2015

 Shit.

[bigs], I'm really sorry. My condolences. Paul.
 — MaxwellBuchanan, Aug 18 2015

Holy shit. Big, I'm so sorry.
 — doctorremulac3, Aug 18 2015

Now I feel guilty...
 — FlyingToaster, Aug 18 2015

 [annotate]

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